Physics notes

FORM ONE

Form 1
1.3.5 Density/relative density
Mass - The quantity of matter in a body. The SI unit is kg
Volume - The amount of space occupied by a substance. The SI unit is m3, for liquids it is litres (l)
Weight - It is the attractive force towards the earth’s center exerted by the earth on the body. Its SI unit is N
Density - The ratio between the mass of an object and its volume
Relative Density - The ratio of the density of a substance to the density of water
Specific Gravity (Relative Density) - The ratio of the density of a substance to the density of a given reference material (i.e. water)
Hydrometer - An instrument used to measure the specific gravity (or relative density) of liquids
Mass(m)

Density Equation:

                             Density =mass

                                           Volume



Density of substance

Relative Density Equation: 

Relative Density =Density of a substance

                                    Density of water

In an experiment using a Hare’s apparatus, the lengths of a methanol column and a water column were found to be 16 cm and 12.80 cmrespectively
Find the relative density ofmethanol


Given h1 = 16cm h2 = 12.80cm
g = 9.8 m/s2ρ2 = 1g/cm ρ1 = ?

At equilibrium: Inside pressure = outside pressure

Step 1: Rearrange for ρ1
1h1 2 h2
2h2
1 h
1
Step 2: Solve for ρ1
112.80
1 16
10.8g /cm
3
Step 3: Solve for relative density
Relative Density Density of substance
Density of water
RD 0.8 0.8
1


If the length of the methanol column was altered to 21.50 cm, what would be the new height of the water column?

Given: h1 = 21.50 cm ρ1 = 0.8 g/cm
ρ2 = 1g/cm h2 = ?

Step 1: Rearrange for h2
1h1 2 h2
h  1h12 
2
Step 2: Solve for h2
h 0.8 21.50 17.2cm
2 1


Force
Concept of force
Force - Any influence that causes a free body to undergo acceleration
Weight - The product of mass times the weight of gravity (W = mg)

Types of force
 1. Attractive force

2. torsional force (torque)

3.stretching (elastic) force

4. compression

5. repulsive

6 frictional force

Attractive Force - A force which brings one object towards another
Torque - A force which twists or rotates an object
Elastic Force - A restoring force that returns a body to its original shape
Compression Force - A force which puts pressure on an object which decreases its size 

Repulsive Force - A force which pushes to magnets apart (ex north pole and south pole)

 Frictional Force - A force which prevents a body from sliding, opposes its movement

Effects of forces
Effects of forces - Changes the speed of an object, changes the size or shape of an object, changes the direction of movement of an object

Archimedes principle and the law of flotation

Archimedes principle
Archimedes Principle - When a body is partially or totally immersed in a fluid it experiences an upward thrust which is equal to the weight of the displaced fluid

Upthrust - The force exerted by a liquid to a body when the body is partially or totally immersed in water
Opposing forces acting on an object which is totally submersed in water - Upthrust, weight of the object

1. A block of metal of density 2700 kg/m3has a volume of 4.0 x 10-2m3. Calculate the
Mass of the block Given: ρ = 2700 kg/m3V = 4.0 x10-2m3

Density Equation: Density=Mass(m)/ Volume(V )


Step 1: Rearrange the density equation for mass (m)
m V
Step 2: Solve for m
m 2700 (4.0 102)
m = 108kg


Apparent weight when immersed in brine of density 1200 kg/m3Given: V = 4.0 x10-2m3
ρ = 1200 kg/m3g = 9.8

Archimedes’s Principle:Upthrust Weightof
Archimedes’s Principle: Upthrust V g
displaced
fluid

Apparent weight Actual weight Upthrust

Step 1: Calculate upthrust
Upthrust (4.0 102) 1200 9.8
Upthrust 470.4N
Step 2: Calculate actual weight
Actual weight 1089.8
Actual weight 1058.4N
Step 3: Calculate apparent weight
Apparent weight 1058.4 470.4
Apparent weight 588N

Law of Flotation
Flotation - A special case when the upthrust is big enough to equal the weight of the object
Law of Flotation - A floating body displaces its own weight of the fluid in which it floats

Structure and properties ofmatter
Structure of matter
Differentiate between solids, liquids and gases -

Solid
Liquid
Gas

Volume
Fixed volume
Fixed volume
Occupies the volume of the container

Motion of Molecules
Molecules vibrate around one position
Molecules move
freely within the liquid
Molecules move with high velocity and
collide with each other and the wall of the container

Intermolecular
Forces
Very strong
Weak
Negligible


Elasticity
Elasticity - The property of a material to return to its original shape and size when the applied force (stretching) is removed
Hooke’s Law (of elasticity) - The extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit. F = -kx
Coefficient of stiffness - The ratio between tension and extension

Adhesion andcohesion
Adhesion - The attraction process between dissimilar substances (ex. dew on a spider’s web) Cohesion - The attraction process between similar substances (ex. water molecules in a drop) Mercury has a high cohesive force

Surface tension
Surface Tension - Is the tangential force in the surface acting normally per unit length across any line in the surface

Capillarity
Capillarity - The action of a liquid rising due to adhesion of the molecules
Applications of capillary action - Kerosene rises up a lamp wick, absorption of water by a towel, rising of water from the soil, use of blotting paper on ink
Viscosity - The force of friction which exists between layers of a liquid or gas
Viscous Liquids - Liquids which are difficult to stir and don’t flow easily (ex honey, turpentine)
Non-viscous Liquids - Liquids which are easy to stir and flow easily (ex water, kerosene)

Osmosis
Osmosis - Passage of molecules through a semi-permeable membrane from a weak to a strong solution

Pressure
Concept ofpressure
Pressure - Is the force acting normally per unit area. Its SI unit is N/m2or Pascal
Paschal’s Principle of Pressure - When a vessel is completely filled with fluid and pressure is applied at the surface, that pressure is transmitted equally throughout the whole of the enclosed fluid
Devices which apply Paschal’s principle - Hydraulic jack, hydraulic press

Pressure due tosolids
1. A rectangular wooden block of density 0.8g/cm3has dimensions 0.5m x 0.8m x 6m. What is the maximum pressure will it exert on the ground?

Given: ρ = 0.8g/cm3or 800kg/m3Volume = 0.8 x 0.5 x 6 = 2.4 m3
g = 9.8

density 
mass


volume

weight mass g
Pressure Weight
Area
Step 1: Calculate mass
mass density volume 2.4 800
mass 1920kg
Step 2: Calculate weight
weight mass g
weight 1920 9.8 18816N
Step 3: Calculate minimum possible area.
This is done because maximum pressure is felt when a body rests on the minimum possible area.
0.5m and 0.8m are the two smallest lengths given
Area = 0.5 x 0.8 = 0.4m2
Step 4: Calculate the maximum pressure
Pressure Weight
Area
Pressure 18816
0.4
Pressure 47040N / m2


Pressure due toliquids
(Not found in exams)

Atmospheric pressure
Atmospheric Pressure - The pressure caused by the weight of the atmosphere above an object
Barometer - An instrument used for measuring atmospheric pressure

Work, energy andpower
Work
Work - Product of the force and distance moved in the direction of the force

Energy
Energy - The quantity which represents the ability to perform work whose SI unit is joules
Types of Energy - Chemical, mechanical, heat, electrical, radiant, kinetic, potential
Chemical Energy - The potential of a chemical substance to undergo a transformation through a chemical reaction to form another substance. The breaking or making of chemical bonds involves absorbing or giving off energy
Mechanical Energy - The sum of potential and kinetic energy in a mechanical system which is associated with the motion or position of an object
Heat Energy - Energy transferred from one body or system to another due to thermal contact when the systems have different temperatures
Electrical Energy - Is the amount of total work that can be done within an electrical system
Radiant Energy - The energy of electromagnetic waves (light)
Kinetic Energy - Energy possessed by a body due to its motion (ex. moving ball)
Potential Energy - Energy possessed by a body due to its position or state (ex. fruit in a tree)
Law of Conservation of Energy - Energy cannot be created or destroyed
Energy transformation examples -
Bullet fired from a gun - Chemical energy from the gun powder is converted into heat energy and then mechanical energy
Battery used to light a bulb torch - Chemical energy in the battery is converted to electrical energy, then heat energy heats the filament and light energy is emitted from the bulb
Power
Power - Work done per unit time

Light
Sources oflight
Luminosity - A measurement of brightness
Luminous Bodies - Produce their own visible light (ex sun, some insects, and stars)
Non-luminous Bodies - Cannot produce light on their own. Material that cannot be seen unless they have been illuminated by a luminous body (ex you cannot see humans unless there is light)
Light Ray - The direction of the path taken by light

Propagation and transmission oflight
Differentiate between transparency, translucency and opaqueness -
Transparency - The physical property of matter which allows light to pass through a material.
Transparent materials are clear (ex. glass)
Translucency - Allows some light to pass through diffusely. Translucent materials cannot be seen through clearly
Opaqueness - No light can pass through the material (ex. metals)

Reflection oflight
Reflection - A phenomena in which the light falling on a boundary separating two media is sent back into the firstmedium
Laws of reflection-
The angle of reflection equals the angle ofincidence
The reflected ray is the in the same plane as the incident ray and to the mirror at the point of incidence

Characteristics of an image formed by a plane mirror - The image or a real object is virtual, a line joining a point on the object and the corresponding point on the image is perpendicular to the mirror, the image is laterally inverted, the image is the same size as the object, the distance of the image from the mirror equals the distance of the image from the mirror

FORM TWO

Staticelectricity
Concept of staticelectricity
Electric Charge (Electrostatic Charge) - A property of matter which causes it to experience a force when near other electrically charged matter
Electrostatic Induction - A redistribution of the electrical charge in an object caused by nearby charges
Electrophorus - A capacitive generator used to produce electrostatic charge by electrostatic induction

Detection ofcharges
(Not found in exams)

Conductors andinsulators
Conductors - Materials which allow electricity to pass through them
Conductivity - Is a measure of a material’s ability to conduct an electric current
Insulator - A material which resists the flow of electric current. The electrons in the material are tightly bonded to their atoms
Properties of an Insulator - Valence band and conduction band are far apart, forbidden gap is wide so that electrons cannot gain enough energy to jump across
Explain the following observations -
After a long flight, a plane may become charged - This is due to friction of the metallic body of the plane with the air and clouds

Capacitors
Capacity - The amount of charge a capacitor is able to hold
Capacitor - A device which stores electric charge. It consists of a pair of conductors separated by an insulator. When there is a potential difference (voltage) across the conductors, a static electric field is created which stores energy
Uses of Capacitors - Used for blocking direct current while allowing alternating current to pass, smoothing out power supplies, to tune radios to particular purposes
Capacitance - The measure of the extent to which a capacitor can store a charge
Factors affecting capacitance - Area of the plates, separation distance between the plates, strength of the dielectric material
Essential features of a capacitor - Two conducting plates, an insulator between the plates Alternating Current (AC) - The movement of electric charge periodically reverses direction Direct Current (DC) - The unidirectional flow of electric charge (flows only one way)

1. A capacitor is labeled with a capacitance value of 470μF and is charged to a potential difference of 10V. Calculate the charge stored by the capacitor

Given: Capacitance, C = 470μF Voltage, V = 10V
Quantity of charge, Q = ?
Quantity of charge in a capacitor: Q CV

Step 1: Solve for Q
Q CV
Q 10 470 4700FV
Step 2: Convert μFV into C
4700FV 4.7 103C

Charge distribution along the surface of aconductor
Lightning Conductor - A metal rod or conductor placed at the top of a building and is connected to the ground through a wire to protect the building from damage caused by lightning

Discuss the charge distribution on
The surface of a solid conductor of an irregularshape
The charge density is higher at sharp points than at other areas

A hollowconductor
The charge is only on the outside surface of the conductor
Passengers in the plane are not charged, but an attendant who opens the door is at risk of becoming charged - This is because the inside of the plane is insulated, but when the door is opened the attendant is at risk of touching the body of the plane

A lightning conductor as clouds pass over spikes on ahouse
The charge density is higher at the end of the spikes, the cloud is negatively charged and the spikes are positively charged

(a) (i) What happens when a wire is connected to a charged capacitor? Also draw a diagram showing this.

The electric current flows and the capacitor is discharged through the wire

(ii) An insulated plate A which has a negative charge is joined to a plate B with a positive charge by using a resistance wire. If a charge of 10-6C flows through the wire of resistance 2Ώ in 10-6seconds, how much heat is dissipated in the wire?



Given: Energy Formula: E 
Q = 10-6C t = 10-6s R = 2Ω
E = ?
Q2R


t


Step 1: Solve for E
Q 2R
E 
t
(106)22
E 
106
E 1062
E 2 106Joules


Current electricity
Concept of currentelectricity

Current - A flow of electric charge or the rate of flow of electric charge (SI unit is ampere, and is measured using an ammeter)

Electrical Conduction - The movement of electrically charged particles through a conductor

Measurements used in circuits 

- Ampere (A), 

-coulomb (C), 

-volt (V), 

-ohm (Ω),

- watt (W)

Ampere (A)

- A steady current which when flowing in two infinitely long, straight, parallel conductors which are 1 meter apart and have negligible areas of cross section cause a force of 2.0x10-7N per meter between the conductors
Coulomb (C) - The quantity of charge which passes any section of a conductor in one second with a current a one ampere
Volt (V) - The p.d between any two points in a circuit where 1 joule of electrical energy is converted when 1 coulomb passes from one point to another
Ohm (Ω) - The resistance of a conductor through which a current of one ampere is flowing when the p.d across it is one volt
Watt (W) - SI unit of power which measures the rate of energy conversion which is defined as one Joule per second
When an electrical potential differenceis placed across a conductor, its movable charges flow, giving rise to an electric current
Simple electriccircuits
(Practical use of circuits, discussion of parallel vs series)
*Note that this information is found in section 3.9.0

Magnetism
Concept ofmagnetism
Magnetism - A force which is applied at an atomic or subatomic level whereby positive magnets and negative magnets attract one another
Magnet - Is a material or object that produces a magnetic field
Magnetic Materials - Materials which are attracted by a magnet and can be made magnets by artificial methods of magnetization (ex steel, cobalt, nickel, iron)
Nonmagnetic Materials - Materials which are not attracted by a magnet and cannot be magnetized by artificial methods of magnetization (ex wood, carbon, plastic)
Magnetic Field - A field of force produced by a magnetic object or particle or by a changing electric field
Magnetic Pole - A point which exists at or near each end of a magnet at which the attractive forces or repulsive forces of the magnet are concentrated
Single Domain - Refers to the state of a magnet where magnetization does not vary across a magnet

Magnetization anddemagnetization
Magnetization - The process causing a material to become magnetic due to an external magnetic field
Methods of making magnets - Stroking, induction, electrical
Stroking Method - One pole of a magnet is rubbed against a metal rod to cause it to magnetize
Induction Method - After a piece of unmagnetized metal is placed near or in contact with a pole of a magnet it will be magnetized
Demagnetization - The causing of a material to lose its magnetic properties due to external forces or through decay over time
Magnetic Induction - The process of producing magnetism in a non-magnetized material when it is placed in a magnetic field
Keepers - Prevents bar magnets from becoming weaker over time due to self demagnetization
Neutral Point - A point in a magnetic field where the resultant field is zero

Reason the strength of a magnet cannot increase beyond a certain limit - When all domains have been oriented in the same direction, no further magnetization is possible which means that the material is saturated
Reason why an increase in temperature weakens or destroyed the magnetism of a magnet - Causes greater atomic vibration which prevents the domain from being aligned in the same direction

Magnetic fields of amagnet
Magnetic Screening - The prevention of a magnetic field from reaching a certain region by surrounding the object with a magnetic material
Magnetic Field - The region around a magnet where the effects of the magnet can be detected

1. Sketch the lines of force between two bars of magnets placed on a horizontal table with:
Their N-poles facing eachother
Note that the arrows always go towards an S pole or away from an N pole
One N-pole facing the S-pole ofanother



Earth’s magneticfield
Earths magnetic field faces north

Forces inequilibrium
Moment of aforce
Moment - The tendency of a force to twist or rotate an object (torque). The SI unit is the Newton Metre
Principle of Moments - If a body is in equilibrium under the action of forces which lie in one plane, the sum of clockwise moments is equal to the sum of anticlockwise moments about any point in that plane

Center ofgravity
Center of Gravity - A point through which the resultant weight of all particles in the body appear to act

Types of equilibrium
Types of Equilibrium - Stable, unstable, neutral
Stable Equilibrium - When a body returns to its equilibrium position after being displaced slightly (Ex a sphere resting on a concave surface)
Unstable Equilibrium - When a body does not return to its equilibrium position after being slightly displaced (a sphere resting on a convex surface)

Neutral Equilibrium - When a body stays displaced after being slightly displaced and gravity exerts no moment about the base (a sphere on a flat surface)
Why racing cars have wide wheel tracks - Increases stability because a wider base makes it more difficult to turn over

1. A uniform half meter ruler is freely pivoted at the 15cm mark and balances horizontally when a body of mass 40g is hung at the 2.0m mark.
Make a clear sketch to show the forces and their positions in thearrangement
Calculate the mass of the half-meterruler

The clockwise moment will be on the right side because it moves the ruler in a clockwise direction. The left side is the anticlockwise moment because it moves the ruler in an anticlockwise direction. The moment is calculated by multiplying the length by the weight for each

Clockwise moment = anticlockwise moment W x 10cm = 40gf x 13cm
10W = 520 W = 52g

Simple machines
Concept of simplemachines
Mechanical Advantage - The factor by which a mechanism multiplies the force or torque applied to it

Mechanical Advantage: MA
outputinput
force force

Velocity Ratio (of a machine) - The distance that the point of effort moved divided by the distance that
point of load moved

Velocity ratio of a machine:VR 
distance of distance of
effort load

Efficiency - The ratio between energy used the total energy supplied. The excess energy is wasted, usually as heat energy

Efficiency Equation: Efficiency 
Energy Used Energy Supplied
100%


1. A hydraulic press has a large circular piston of radius 0.8m and a circular plunger of radius 0.1m. A force of 200N is exerted by a plunger.
Find the force exerted on the piston. Also, state one reason why the weight of the load raised by the piston is much less than the force exerted on thepiston.
Given: Radius of hydraulic press, RH = 0.8m Radius of plunger, RP = 0.1m
Force of plunger, FP = 200N Force of hydraulic press, FH = ? Pi = 22/7 or 3.14
Area of a circle: A r 2
Force: F P A or P F
A
Step 1: Calculate areas of the piston and hydraulic press
A 22 0.120.031m 2
P 7
Step 2: Calculate the power of the plunger
P FP 200 6451.61N / m 2
AP 0.031
Step 3: CalculateFH


A 22 0.822.011m2
H 7
FH P AH 6451.612.011 12974.2N


If the plunger is moved through a distance of 0.64m while exerting its force, what distance will the piston be raised?
Given: Area of hydraulic press, AH = 2.011m2Area of plunger, AP = 0.031m2
Height moved by plunger, hP = 0.64m Height moved by hydraulic press, hH = ? Volume = Area x Height

Since the volume moved by the plunger equals the volume moved by the hydraulic press, we can set up an equation where they are equal to each other and use it to solve for the distance moved by the piston

AP hP AH hH

Step 1: Rearrange for hH
h AP hPH A
H
Step 2: Solve for hH
h 0.0310.64
H 2.011
hH 0.01m

Motion in a straightline
Distance anddisplacement
Uniform Velocity - A motion with zero acceleration in a given direction
Uniform Acceleration - A constant rate of change of velocity

Speed andvelocity
Speed - Is the magnitude of an objects velocity, or the rate of change of an objects position. It is a scalar quantity with an SI unit of m/s
Velocity - Is the measure of the rate of change of an objects position. It is a vector quantity with an SI unit of m/s in a certain direction
Velocity Ratio (VR) - Distance moved by effort per distance moved by load
Terminal Velocity - Occurs when an object’s speed is constant due to the restraining force exerted by air (the maximum velocity of a falling object in air)

Acceleration
Acceleration - The rate of change of velocity

Equations of uniformly acceleratedmotion
50g mass is placed on a straight track sloping at an angle of 45 to the horizontal as shown in the figure below. Calculate:

The acceleration of the load as it slides down the slope Given: Mass, m =55g
Inclination, 45°
Weight parallel to slope, mg sin(45°) Weight normal to slope, mg cos(45°)

Normal reaction, R = mg cos(45°) F = mg sin(45°)
g = 9.2 m/s2a = ?
Force Law: F ma

First we redraw the picture with this information
Step 1: Use the force law. Note that the masses cancel out
mg sin(45) ma
Step 2: Solve for a
a g sin(45)
a 9.8 sin(45)
a 6.93m / s 2


The distance moved from rest after 0.2seconds Given: u = 0
Time, t = 0.2
Acceleration, a = 6.93m/s2Distance, S = ?

Distance Equation: S ut 
1 at 2
2


Step 1: Insert values of variables
S 0 0.2 1 6.93(0.2) 2
2
Step 2: Solve for S
S 0 1 6.93(0.2) 2
2
S 0.14m


(a) Sketch the diagram of a body which starts from rest and accelerates uniformly for some time to a constant velocity and then maintains this velocity for a certain period of time before decelerating uniformly to astop.

(b) A car moving with a uniform velocity of 100m/s is decelerated at 2.5m/s to a stop. Calculate:
(i) The time taken for the car to stop

Given: Initial velocity, u = 100 m/s Final velocity, v = 0 m/s

a = -2.5 m/s2t = ?

This is equation means that the final velocity is equal to the initial velocity plus the acceleration over time
v = u + at

Step 1: Rearrange for t
t v u
a
Step 2: Solve for t
t 0 100
2.5
t = 40 seconds

(i) The distance traveled by the car before it is brought to rest Given: v2= u2+ 2aD
Distance traveled, D = ?

Step 1: Rearrange for D
v 2u 2
D 
2a
Step 2: Solve for D
021002
D 
2(2.5)
D = 2000m


Motion undergravity
Newton - Unit of force where 1 Newton gives a body of 1kg an acceleration of 1m/s2
Conditions under which g can denote acceleration or the amount of force -
Acceleration - For gravity g is represented in SI units as m/s2under the condition that a body is undergoing free fall
Force - For force g is represented in SI units as N/kg (force (N) per kilogram (kg)), under the condition that the mass is 1kg
Force due to gravity on earth - 9.8 or 10 m/s

1. (a) A rocket taking off vertical pushes out 25kg of exhaust gas every second at a velocity of 100m/s. If the total mass of the rocket is 200kg,
What is the resultant upward force on the rocket?Given: mrocket =200kg

m
Rate of exhaust flow (
t
v = 100 m/s vo = 0 m/s

) = 25kg/s

Newton’s Second Law of Motion: F Rateof change of momentum
m
Newton’s Second Law of Motion: F t (v vo)
m
Step 1: Solve for F.Note that is given inthe
t
problem as 25kg/s
F m (v v )
t o
F 25 (100 0)
F 2500N


What is the upward acceleration of therocket?
Given: F = 2500N mrocket = 200kg
a = ?
Force Law: F ma

Step 1: Rearrange for a
Step 2: Solve for a




(b) Calculate the acceleration of the rocket in (a) above when it has burned off 100kg of fuel
To find the new mass of the rocket, you subtract the burned fuel from the original mass of the rocket

Given: m = 200kg - 100kg = 100kg F = 2500N
Force Law: F ma

Step 1: Rearrange for a
a F
m
Step 2: Solve for a
a 2500
100
a =25m/s2

Newtons laws ofmotion
1stLaw ofmotion
1st- Every body persists in its state of being at rest or of moving uniformly straight forward unless it is compelled to change its state by an outside force

2ndLaw ofmotion
2nd- The rate of change of momentum of a body is proportional to the applied force and takes place in the direction of the force

Conservation of linearmomentum
Momentum - The product of the mass and velocity of an object. Its SI unit is kg*m/s
Principle of Conservation of Momentum - When bodies in a system interact, the total momentum remains constant provided that no external forces act upon the system
Impulse - The change in momentum of a body when a force has been applied to it. Its SI unit is Ns (Newtons x seconds)

3rdLaw ofmotion

3rd- To every action there is an equal and opposite reaction
Temperature
Concept oftemperature
Temperature - A quantitative measurement of hot or cold. Its SI unit is Kelvin (K)
Absolute Zero - The temperature at which atoms stop moving, thereby causing the volume of a gas to drop near zero. It is measured as 0K

Measurement oftemperature
Thermometer - An instrument which measures temperature
Fundamental Interval of a Temperature Scale - The difference in temperature between the upper fixed point and the lower fixed point
Upper Fixed Point - The temperature of steam from water boiling under standard atmospheric pressure of 760 mmHg
Lower Fixed Point - The temperature of pure melting ice under standard atmospheric pressure of 760 mmHg
Advantages of mercury over alcohol as a thermometric liquid - Does not vaporize easily, expands steadily, Hg is a better conductor of heat, has a higher boiling point, does not cling to the glass inside the thermometer, it is opaque and easier to read
Similarities between maximum and minimum thermometers - Perform one way measurement, contain steel indices
Differentiate between maximum and minimum thermometers -
Maximum Thermometer - Records the maximum temperature reached during a certain period of time.
It uses mercury in a glass thermometer

Minimum Thermometer - Records the minimum temperature reached during a certain period of time.
It uses alcohol in a glass thermometer

1. Determine the final temperature obtained when 500g of water at 100°C was mixed with 500g of water at 10°C and well stirred (Note: The specific heat capacity of water is 4200 J/(kg°C)
NECTA 2007 4c

Note that since the masses of the two samples of water are the same, you can just average the temperatures to get 55°C ((100+10)/2)


Sustainable energysources
Water/solar/wind/sea/geothermalenergy
Types of renewable energy - Wind, geothermal, solar, sea wave
Wind Energy - Energy derived from the Earth’s winds
Geothermal Energy - Energy derived from the internal processes of a planet
Solar Energy - Energy derived from a stars radiant energy Sea Wave Energy - Energy derived from waves in the oceans Water Energy - Energy derived from falling water (ex. HEP)
Anemometer - An instrument used for measuring wind speed
Wind Vane - An instrument used for showing the direction of the wind

FORM THREE
Applications ofvectors
Scalar and vectorquantities
Scalar Quantity - A quantity which is not associated with a direction Vector Quantity - A quantity which is associated with a direction Speed vs. Velocity -
Speed - Refers to the distance covered per unit of time without specifying direction (scalar)
Velocity - Refers to the distance covered in a given direction per unit of time (vector)

Relative motion
Relative Velocity - The vector difference between two velocities of two objects

Resolution ofvectors
Resolution of vectors - To resolve vectors into two components (vertical and horizontal)
Parallelogram Law of Forces - If two forces are represented in magnitude and directions by an adjacent side of a parallelogram, then their resultant is represented in magnitude and direction by the diagonal of the parallelogram
Triangle Law of Forces -
(Add vector problems)

Friction
Concept offriction
Friction - The force resisting motion between surfaces which are sliding against each other by converting kinetic energy into heat (ex a block moving down an inclined plane)
Coefficient of friction - A scalar quantity which describes the ratio of the force of friction between two bodies and the force pressing them together
Ways of reducing friction - Using a lubricant like oil/water/grease between two solid surfaces, streamlining, polishing surfaces, separating surfaces by air, uses rollers or ball bearings
Advantages of friction - Allows walking, cars can brake, used to for parachutes
Limiting Friction - The maximum value of frictional force exerted between two surfaces not moving relative to each other
(Add friction problems)

Types of friction

Types of friction - Dry, fluid, lubricated, skin, internal
Dry - Resists relative lateral motion of two solid surfaces incontact
Fluid - Friction between layers within a viscous fluid that are moving relative to each other Lubricated - Friction which occurs when a fluid separates two solid surfaces (ex oil in a motor) Skin - The force resisting the motion of a solid body through afluid
Internal - The force resisting motion between elements of a solid material as it deforms

Laws of friction
Laws of Friction -
Amontons’ 1stLaw - The force of friction is directly proportional to the applied load Amontons’ 2ndLaw - The force of friction is independent of the apparent area of contact Coulomb’s Law of Friction - Kinetic friction is independent of the sliding velocity

Light
Reflection of light from curvedmirrors
Concave Mirror - Has a reflecting surface that bulges inward (away from the incident light) and reflect light inward to one focal light (they focus light)
Convex Mirror - A mirror in which the reflective surface bulges towards the light source, scattering the light
Plane Mirror - A flat mirror
Principle Focus - The point where light rays originating from a point on an object converge with one another
Incident ray of light - The ray of light leaving the mirror after reflection
Radius of Curvature - The distance from the vertex to the centre of curvature of the surface
Principle Axis - The main axis of the lens or mirror
Pole - A point that describes the position and orientation of a line with respect to a given circle
Differentiate between real and virtual images -
Real Image - A representation of an object in which the perceived location is actually a point of convergence of the rays of light that make up the image (ex. images on a cinema screen)
Virtual Image - An image in which outgoing rays from a point on the object always intersect at a point (ex. an image in a flat mirror)
Characteristics of an image formed by a convex mirror - The image is virtual, erect and smaller than the object, except if the object is closer than the focal point
Characteristics of an image formed by a concave mirror - The image is always real except when the object is between the focal point and the mirror, the image is always inverted, the size depends on the distance from the mirror
Position of an image in a concave mirror of a distant object - It is formed at the principle focus

1
Lens Formula:
f
1 1
u v


Refraction oflight
Refractive Index - The ratio of the speed of light to the medium
Refraction - A change in the direction of a wave due to a change in its speed. For light it is the change of speed of light (and hence its direction) due it entering a different medium
Total Internal Reflection - An optical phenomenon which occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected
Angle of Incidence - The angle formed between the incident ray and the normal a the point of incidence
Normal (to a flat surface) - Is a vector that is perpendicular to that surface
Critical Angle - The angle of incidence above which total internal reflection occurs. It is measured with respect to the normal
Conditions necessary for total internal reflection - Light must be passing from a dense medium to one which is less dense, the incident light must be greater than the critical angle of the medium
Conditions giving rise to a critical angle - Light travels from a dense medium to one which is less dense and is refracted at 90°
Cause of refraction of light when passing through transparent media - This is due to the fact that light changes velocity when moving from one medium to another
Mirage - A naturally occurring optical phenomenon where light rays are bent to produce a displaced image of distant objects or the sky

Why a swimming pool appears shallower than its depth - It happens because light rays bend as they pass from water to air. When they pass from water to air, they are reflected with an angle of refraction greater than the angle of incidence

1. Three slabs of different types of glasses are placed on a table one on top of the other in the following order from below:
Slab
Refractive Index
Thickness

A
1.4
1.2cm

B
1.5
1.8cm

C
1.6
0.8cm

Where will the mark on the table appear to be?
Given: μA = 1.4 μB = 1.5
μC =  1.6 DA = 1.2cm DB  =1.8cm
DC  =0.8cm
D represents real depth and d represents apparent depth
Real depth(Da )


Real Depth: 
Apparent depth(da )


Position Total real depth Total apparent depth
 DA
A d
A

Step 1: Rearrange for dA
d DA
A 
A
Step 2: Solve for dA, dB and dC
d 1.2 0.86cm
A 1.4
d 1.8 1.2cm
B 1.5
d 0.8 0.5cm
C 1.6
Step 3: Solve for position
Position Total real depth Total apparent depth
Position (1.2 1.8 0.8) (0.86 1.2 0.5)
Position 1.24cm


Refraction of light by a rectangularprism
(Not found in exams)

Refraction of light by a triangularprism
(Not found in exams)

Colours oflight
Primary Colours - Sets of colours which can be combined to make a useful range of colours
Secondary Colours - A colour made by mixing two primary colours
Complimentary Colours - Colours which when added together form white light
Additive Colour - The use of red, green or blue light to produce other colours by combining them together.
This is used in projectors
Subtractive Colour - The colour that the surface displays are the colours which are reflected by the material. This is used in the mixing of paints, dyes and inks. The colours used are generally cyan, magenta and yellow
Chromatic Aberration - A type of distortion in which there is a failure in the lens to focus all colours to the same convergence point due to lenses having different refractive indexes for different wavelengths of light
Fluorescence - The emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength

Why objects appear coloured - An object with colour tends to reflect light of its colour and absorbs the rest. The colour seen by a person is the colour which was reflected back
Why mixing two paint colours is different than mixing two of the same colours of light (ex blue and yellow) - Pigments in paint absorb light, so the yellow pigment will absorb blue light and reflects yellow/red/green, while the blue pigment absorbs yellow and red light and reflects blue/green. Since the only common colour between the two that is being reflected is green, the colour reflected will be green (this is mixing by subtraction). Blue and yellow light are complementary colours so they add to form white light (this is mixing by addition)

Refraction of light bylenses
Principle focus of a convex lens - The point on the principle axis where all rays originally parallel and close to the axis converge
Cause of a blurred image in a concave mirror or convex lens - This is caused by light rays not coming together at the same focus

(a) In the following figure are two convex lenses correctly set up as a telescope to view a distantobject.
One lens has a focal length of 5cm and the other has a focal length of 100cm

What is A called and what is its focallength?
A is called the objective lens and has a focal length of 100cm. The objective lens has a longer wavelength than the eyepiece lens
How far from A is the first image from the distantobject?
The image of the distant object is formed at the focus which is 100cm
What is the name of B?
Eyepiece lens
What acts as the object for B and how far must B be from it if someone is looking through the telescope wants to see the final image at the same distance as the distantobject?
The image of A acts as the object for B and therefore must be at the focus of B which is 5cm away
What is the distance between A and B with the telescope set up in partiv?
The distance between A and be is the sum of their focal lengths, 100cm + 5cm = 105cm

Show by a ray diagram how a suitable placed eye sees an image of a point object which is placed 10cm in front of a plane mirror. Show clearly the position of the image and give two reasons why it is a virtual image.

This image is virtual because it cannot be formed on the screen and there is no actual intersection of light rays when the image is formed

Calculate the critical angle for light emerging from glass of refracting index 1.55 into airGiven: Refractive index, gηa =1.55
r = 90°
Critical angle, c = ?
sinc
Critical Angle:g    a sinr


Step 1: Rearrange for sin c
sincsinrsin9040.2oag 1.55
Step 2: Solve for theangle
sin c sin 90 40.2o
1.55


(a) Explain with ray diagrams the use of the followinglenses
As a magnifyingglass
Convex lens
The position of the object (O) is between the principle focus (F) and the lens
In acamera
Convex lens
The position of the object is beyond 2F

State the characteristics of the images formed in (a)above
The image is virtual, larger than the object, on the same side as the object and iserect
The image is real, smaller than the object, between F and 2F and isinverted

A screen is placed 80 cm from an object. A lens is used to produce on the screen an image with a magnification of 3. Calculatethe
Distance between the object and thelens

Given: Magnification = 3
u is the object distance, v is the image distance from the lens u + v = 80cm

Step 1: Solve for v
m v
u
3 v
u
v 3u
Step 2: Solve for u by substituting v
u + v = 80cm u + 3u = 80cm 4u = 80cm
u = 20cm



Focal length of thelens
Given:LensFormula: 
f
1 1
u v

u = 20cm
v = 3u (from above) = 3*20 = 60cm

f = ?

Step 1: Insert v into the equation
1 1 1
f u 3u
Step 2: Insert values of u and 3u
1 1 1
f 20 60
Step 3: Add the fractions
1 3 1
f 60 60
Step 4: Cross multiply
1 4
f 60
4 f 60
f 15cm


A telescope of 5m diameter reflector of focal length 18.0m is used to focus the image of the sun. Using the distance of the sun from Earth and the diameter of the sun as 1.5x1011m and 1.4x109m respectively, calculate the diameter of the image of thesun

Given: Object distance, u = 1.5x1011m Object diameter, d = 1.4x109m
Focal length, f = 18m v = f = 18m


Magnification Equation:
Image distance Object distance
, m v
u


First you need to find the magnification
Step 1: Solve for m
m 18 1.51011
m = 1.2x10-10
Now you can find the diameter of the sun
Given: d = 1.4x109m m = 1.2x10-10
d’ = ?


Magnification Equation:
Image diameter Object diameter
, m d '
d

Step 1: Rearrange for d’
d ' m d
Step 2: Solve for d’
d'(1.21010)(1.4109)
d’ = 0.168m


Opticalinstruments
Simplemicroscope
(Not found in exams)

Compoundmicroscope
(Not found in exams)

Astronomicaltelescope
Physics principles used to make telescopes - Reflection, refraction

Projectionlantern
(Not found in exams)

The lenscamera
Differentiate between images formed in plane mirrors and a pinhole camera -

Plane Mirror
Pinhole Camera

Image isvirtual
Image is the same size as theobject
Image is laterallyinverted
Image is as far from the mirror as the actual object is
The image isreal
The image is smaller in size(scaled)
Image is verticallyinverted
Image distance is determined by the length of thebox


The humaneye
(Not found in exams)

Thermalexpansion
Thermalenergy
Heat - The energy transferred from one body to another due to contact when they are at different temperatures
Sources of heat in daily life - The sun, electric circuits (in appliances), engines, our bodies
Differentiate between heat and temperature -
Heat
Temperature

The amount of internal energy possessed by a body
Flows from a point with high temperature to one with a lowtemperature
Measured in Joules(J)
Is the measure of hotness or coldness of a body
Does not flow, varies as the quantity of heat in the body or substancevaries
Measured in Celsius (°C), Fahrenheit or Kelvin


Thermal expansion ofsolids
Coefficient of Linear Expansion - Fractional change in linear dimensions (length/radius) per unit temperature change (°C or °K). Its SI unit is length / °C

Thermal expansion ofliquids
Apparent Expansivity of Water - The fractional increase in volume of water as it expands due to a temperature rise in a heated vessel
Anomalous Expansion of Water - The tendency of water to expand as it is cooled below 4°C

Thermal expansion ofgases
Ideal Gas - A theoretical gas composed of a set of randomly moving particles which obeys the ideal gas law
Ideal Gas Law - The equation of a state of a hypothetical ideal gas which approximates the behaviour of many gases under varying conditions combining Boyle’s Law and Charles’s Law
Boyle’s Law - Describes the inversely proportional relationship between pressure and volume of a gas (as volume increases, pressure decreases)
Charles’s Law - A law which describes how gases tend to expand when heated, showing the direct relationship between temperature and volume (as temperature increases, volume increases)
Kinetic Theory of Gases - Explains the behaviour of gases based on the movement of their molecules
Avagadro’s Hypothesis - Requires that equal volumes of all ideal gases have the same number of molecules at STP
Why gases have pressure - When gases travel in a container they hit the walls which exert a force on the walls (pressure) As the temperature rises, the molecules move faster, thereby hitting the wall more often which increases the pressure. As the temperature decreases, the molecules move slower and hit the wall less often which decreases the pressure
Why diffusion happens in gases - Molecules in gas move randomly and when they collide with each other, they bounce in different directions. This causes molecules to move from areas where there are a lot of collisions to areas where there are very little collisions (moving from an area of high concentration to an area of low concentration)
Transfer of thermalenergy
Conduction of heat
Thermal Conduction - The transfer of thermal energy between neighbouring molecules in a substance due to differences in temperature
Thermopile - An electronic device that converts thermal energy into electrical energy

Good conductors of heat - Metals like copper, aluminum, iron, silver, led
Bad conductors of heat - Nonmetals like diamonds, rubber, glass, cork, paper

Convection
Convection - The movement of molecules within liquids or gasses
Kinetic Energy - The energy possessed by a body due to its motion
How kinetic energy is related to temperature of gases - The kinetic energy of gas molecules is proportional to the temperature of the gas

Radiation
Thermal Radiation - Electromagnetic radiation emitted from a material due to its temperature
Good emitters/absorbers of radiant heat - Things with dark colour, metals like copper, iron, silver, led
How heat loss in a thermos flask is prevented -
By Conduction - The flask is made of glass which is a poor conductor of heat, the stopper is made of wood/rubber/cork which are bad conductors of heat, the supporting pad is made of rubber which is a poor conductor of heat
By Convection - There is a vacuum between the walls of the flask. Also by closing the flask at the top by using a stopper
By Radiation - Using silvered walls to reflect infrared radiation back into the thermos flask

Measurement of thermalenergy
Heatcapacity
Specific Heat Capacity - The measurable physical quantity for the amount of heat required to change a body’s temperature by a given amount. Its SI unit is joules per Kelvin (J/K)
Differentiate between heat capacity and specific heat capacity -
Heat Capacity (Thermal Capacity) - The amount of heat required to raise its temperature by 1K
Specific Heat Capacity - Heat required to raise the temperature of a unit mass of the substance by 1K
Explain the following observations -
Gas thermometers are more sensitive and accurate than liquid thermometers - This is due to gases having a lower specific heat capacity than liquids
Alcohol is used in glass thermometers in Arctic regions - This is due to alcohol having a lower freezing point than mercury
A house with thick walls is likely to be cooler during the hot season - This is because a thick wall will conduct less heat from the outside into the house
Level of liquid being heated in a vessel first falls before starting to rise - This is because the vessel expands first, which increases the internal volume, causing the liquid to fall
Linear Expansivity - The faction of its original length by which a rod of the substance expands per Kelvin rise in temperature
Coefficient of Linear Expansivity - The fractional increase in length per degree centigrade rise in temperature
Applications of Bimetallic Strips - Making thermostats, bimetallic thermometers, indicators
200g of a liquid at 21°C is heated to 51°C by a current of 5A at 6V for 5 minutes. What is the specific heat capacity of theliquid?

Given: m = 200g or 0.2kg Initial temperature = 21°C Final temperature = 51°C I = 5A
V = 6V
t = 5 min or 300s
Heat gained by a liquid =mc
Heat supplied by a current =IVt
Heat supplied = Heat gained

First we calculate the heat gained, then heat supplied and then we can solve for the heat capacity

Step 1: Calculate heat gained
mc
5 6 300 9000J
Step 3: Solve for heat capacity (c)
Heat supplied = Heat gained


(0.2)c(5121)6ckgC
Step 2: Calculate heat supplied
IVt
6c 9000
c = 1500 J/kg°C


A tin contains water at 290K and is heated at a constant rate.   It is observed that the water reaches boiling point after 2 minutes and after another 12 minutes it is completely boiled away. Calculate the specific latent heat of thesteam

Given: T1 = 290K
Boiling point of water = 373K
Time to reach boiling point, t1 = 2 min Time to boil away, t2 = 12 min
Specific heat capacity of water, c = 4200 J/kgK Specific latent heat of steam, L = ?
Heat gained by a liquid = mcT
Power Heat
t
Power t m L

Note that the mass of the water (m) will cancel out, since mass is not important in finding the specific latent heat of a substance. The specific latent heat will be the same no matter what the mass is

Step 1: Solve for heat
mcT
m 4200 (373 290) 348600m J
Step 2: Solve for power
Power Heat
t
Power 348600m 174300m J / min
2
Step 3: Solve for specific latent heat (L). Note that the masses cancel out during this step
Power t m L
174300m 12 m L
L = 2,091,600 J/kg


(a) A compound strip of brass and iron is straight at room temperature. Draw a labeled diagram to show its appearance when it hasbeen:
(i) Heated to a high temperature and cooled below 0°C

(b) A compound strip of brass and iron 10cm long at 20°C is held horizontally with iron on top. When heated from below by a Bunsen burner, the temperature of the brass is 820°C and the iron is 770°C. Calculate the difference in lengths of the iron and brass


Given: Lo = 10cm αB = 1.9x10-5
LBo = 10cm
ΔTB = 820 - 20 = 800°C αI = 1.2x10-5
LIo = 10cm
ΔTI = 770 - 20 = 750°C
Linear coefficient of expansion: 




L Lo T

LB BLB o TB
L (1.9 105) 10 800
B
LB 0.152cm
Step 3: Solve for LI (change in iron length)
LI ILI o TI
L LB LI
L 0.152 0.09
L 0.062cm


Change ofstate
Latent Heat - Refers to the amount of energy released or absorbed by a chemical substance during a change of state that occurs without changing its temperature (ex. phase change from ice to water or water to steam)
Specific Latent Heat of Fusion - The amount of heat energy absorbed when a unit mass of a substance changes from a solid state to a liquid state at a constant temperature

1. A block of aluminum, 500g at 20°C was heated in a furnace until just when it melted
Find the total quantity of heat required Given: Mass of block, m = 500g or 0.5 kg Initial temperature, To = 20°C =293K
Final temp, T = 660°C = 933K (This is the melting point of aluminum) Latent heat of fusion of aluminum, LAl = 3.2 x105JKg
Specific heat capacity of aluminum, Cal = 920K/JKg
Heat required to melt aluminum: mcAl T mLAl or m(cAl T LAl )

Step 1: Calculate ΔT
T 933 293 640
Step 2: Solve for heat required
m(cAl T LAl )
0.5((920 640) (3.2 105))
heat 454400J

If in this process the furnace consumes 100 litres of gas of calorific value 16800J/litres. Find its efficiency.
Given: Volume of the gas, 100 litres Calorific value of the gas = 16800J/litre Energy Absorbed = 454400J
Energy Supplied: Energy Supplied Given Volume Calorific Value
Energy Absorbed

Efficiency Equation: Efficiency 
Energy Supplied
100%


Step 1: Calculate energy supplied
Energy Supplied 100 16800
Energy Supplied 1680000J
Step 2: Calculate efficiency
Efficiency 454400 100 27.05%
1680000


Vapour andhumidity
Vapour
Evaporation - Causes the vapourization of a liquid, but occurs only on the surface of a liquid Condensation - The change in the phase of matter from gaseous to liquid droplets Saturated Vapour - A vapour which is in equilibrium with its liquid or solid
Unsaturated Vapour - A vapour which has not reached the state of dynamic equilibrium with its own liquid or solid
Factors effecting evaporation - Humidity, temperature, barometric pressure, surface area
Triple Point of Water - The temperature where all three states of water (liquid, gas (vapour), solid (ice)) exist in equilibrium
When a person perspires on a hot day, evaporationoccurs and helps to cool the body Warm air can hold more water vapourthan cold air
Behaviour of a molecule in a liquid undergoing evaporation and then condensation - The molecule gains enough energy to escape the surface of the liquid through (evaporation). After it has escaped it

eventually loses energy and slows down, falling back into the liquid or forming droplets of the liquid elsewhere (condensation)
Differentiate between evaporation and boiling -
Evaporation
Boiling

Occurs only on the surface of theliquid
Takes place at alltemperatures
Occurs throughout theliquid
Boiling occurs at a specific temperature depending on thepressure


Humidity
Hygrometer - An instrument used to measure relative humidity
Dew Point - Temperature at which water vapour present in the air is sufficient enough to saturate it How dew is formed - As the surface of something cools by radiating its heat, atmospheric moisture condenses at a greater rate than it evaporates, resulting in the formation of water droplets
Relative Humidity - The measure of the amount of water vapour in the atmosphere

Current andelectricity
Electromotive force (emf) and potential difference(pd)
Voltmeter - An instrument used for measuring the electric potential difference between two points in an electric circuit
Electric Potential - A point in space where the electrical potential energy divided by the charge that is associated with an electric field. It is a scalar quantity measured in volts or joule/coulomb
Electromotive Force (e.m.f) - The force which tends to cause current to flow
Potential Difference (p.d) - Is the potential difference between two terminals of a cell when the cell delivers current to the external circuit. Potential difference is always smaller than the electromotive due to resistance of the cell
Volt - The SI unit of the electromotive (e.m.f) force and the electric potential difference
Types of electric circuits - Open circuits, closed circuits
Open Circuits - A circuit which lacks a complete path between the positive and negative terminals of its power source
Closed Circuits - A circuit which has a complete path between the positive and negative terminals of its power source
Galvanometer - An instrument used for detecting and measuring electric current Shunt - A device which allows electric current to pass around a point in a circuit Motor - A machine which converts electrical energy into mechanical energy Dynamo - A generator that produces direct current with the use of a commutator
Commutator - A rotary electrical switch in certain types of motors or generators which periodically reverse the current direction between the rotor and external circuit
Generators - A device which converts mechanical energy into electrical energy
Accumulator - An apparatus used to store energy
Examples of accumulators - Rechargeable batteries, capacitors, hydraulic accumulators
How you know it’s necessary to recharge an accumulator - The stored charge has been depleted

A moving coil galvanometer of 30Ω resistance which carries a maximum current of 15mA can be converted into anammeter
How can the galvanometer be made to give amperereadings?
A galvanometer can be made to give ampere readings by connecting it in parallel to a low resistance called a shunt
If the device is to give 1.5A full scale deflection (f.s.d), what value resistance will berequired?

Given: Current of device, I = 1.5A Current in section g, Ig = 15mA or 0.015A Current in section s, Is =?
Resistance of galvanometer, Rg = 30Ω Resistance of resistor s, Rs = ?

Current in the circuit: I I s I g
I s Rs I g Rg
First we need to calculate the current in section S (Is)

Step 1: Rearrange for Is
I s I I g
Step 2: Solve for Is
I s 1.5 0.015 1.485A


Now we can solve for Rs

Step 1: Rearrange for Rs
R  I g Rgs I
s
Step 2: Solve for Rs
R 0.015 30 0.303
s 1.485


The figure below shows two coils X and Y. X is connected to a battery and Y is connected to a center zero galvanometer G.
State and explain the deflection of the galvanometer needle when the switch K is closed for a few seconds and thenopened.

If switch K is closed the galvanometer will deflect and then return to zero. When switch K is opened the galvanometer will deflect in the opposite direction and then return to zero. Deflection happens when K is opened and closed because this is when the flux changes in X and Y since the induced e.m.f depends on the rate of change of flux

Why must the galvanometer be a center zerotype?
This is so that it can read deflections on either side

What would be done in X to increase the current induced inY?
To increase the induced current in Y you need to increase the number of turns of X

Resistance to electriccurrent
Ammeter - A measuring instrument which measures the electric current in a circuit
Resistor - A two terminal electronic component that produces a voltage across its terminals that is proportional to the electric current in accordance with Ohm’s law (V = IR)
Thermistor - A type of resistor whose resistance varies significantly with temperature
Rheostat - A two terminal variable resistor used to vary resistance in a circuit
Resistivity - Is a measure of how strongly a material opposes the flow of an electric current
Ohm’s Law - Current flowing through a conductor is directly proportional to the potential difference (p.d) across the conductor provided that the physical state of the conductor remains unchanged
Limitations of Ohm’s Law - Does not apply to some electrolytes (Ex dilute H2SO4), does not apply to conduction in gases, does not apply to semiconductors (diodes and transistors)
Ohm’s law is not applicable when physical conditions of the wire are altered
Factors affecting resistance of a wire - Length, resistivity, cross sectional area

Length of wire (resistance increases with increasing length (R l)
Resistivity/nature of the wire (resistance increases as resistivity increases (R 

R )
A

Cross section area of the wire (resistance decreases with increasing cross section area of a
1
wire(R )
A
l
Resistance of a wire: R 
A
In the circuit shown in figure 1, the battery and ammeter have negligible internal resistance. What will be the ammeter reading?
Since part A and B are in parallel, you will add their inverse. In part B there are two resistors in series, so their resistances will be added
Part A: 1 Ω
Part B: 1 Ω + 3 Ω = 4Ω
Ammeter Reading Part A PartB
Ammeter Reading 21 1 2.5A

 
 
In the circuit shown below, the total resistance between X and Y is 2.0 Ω. Calculate the unknown resistanceQ




Given:
1  1  1
R R1 R2
...

RXY = 2Ω Q = ?
Note the denominator is 10 because the 6Ω and 4Ω resistors are in series so they are added 6 + 4 = 10

Step 1: Insert values into the equation for parallel resistors
1 1  1
RXY 10 Q
1  1  1
2 10 Q
Step 2: Subtract the fractions
1 1 1
Q 2 10
1 5 1
Q 10 10
Step 3: Cross multiply
1 4
Q 10
4Q 10
Q = 2.5 Ω


(2b) A 2.0m long resistance wire of cross section 0.5mm2has a resistance of 2.2Ω. Find the:
Resistivity of thematerial

Given: l = 2m
A = 0.5mm2or 5x10-7m2R = 2.2 Ω
ρ = ?

Step 1: Rearrange for ρ
R l
A
RA
l
Step 2: Solve for ρ
2.2 (5 107)
2
5.5 107Ωm



Length of the wire that would give a total resistance of 1.0 Ω when placed inparallelGiven: R1 = 2.2Ω
RT = 1 Ω RX = ?
1 1 1
RT R1 RX
First we need to find the resistance of the wire, then we can find the length

Step 1: Use the equation for parallel resistors
1 1 1
1 2.2 RX
Step 2: Subtract the fractions
1 2.2 1
RX 2.2 2.2
Step 3: Cross multiply
1   1.2
RX 2.2
1.2RX = 2.2 RX  = 1.833Ω


Now we need to solve for the length l

Given: R = 1.833Ω ρ = 5.5x10-7Ωm
A = 5x10-7m2
l = ?
R l
A

Step 1: Rearrange the equation for l
l RA

Step 2: Solve for l
1.833 (5 107)
l 
5.5 107
l = 1.66m

A 5Ω resistor and a 1Ω resistor are connected in parallel to a cell of e.m.f 6V and have an internal resistance of 0.5Ω. Calculate the current flowing around thecircuit.

Given: E = 6V R = ?
r = 0.5Ω I = ?
Energy in a circuit: E I (R r)

First we must solve for R
Step 1: Use the equation for parallel resistors
1  6
R 5


1  1 1
R 5 1
115
R 5 5
Step 2: Solve for R
R 6
5


Now we can solve for I

Step 1: Rearrange the equation for I
I ER r
Step 2: Solve for I
I 6 4.5A
5 0.5
6


A wire of uniform cross sectional area has a length of 10m, a resistance of 2Ω and a resistivity of 2x10-7Ωm. What is the cross sectional area inm2?
Given: l = 10m R = 2Ω
ρ = 2x10-7Ωm
Resistance of a wire: R l
A
Step 1: Rearrange for A
A l
R
Step 2: Solve for A
(2 107) 10
A 
2
A 1106m2


(a) If you are provided with resistors of 5Ω, 10Ω and 20Ω. What are the maximum and minimum resistances which can be obtained by connecting theseresistors?

Note that maximum resistance occurs when all three resistors are connected in series and minimum resistance occurs when all three resistors are connected in parallel

Maximum
R R1R2 R3 R51020 R 35
Minimum
1 1 1 1
R R1 R2 R3
1111
R 5 10 20
1 4 2 1 7
R 20 20 20 20
R 20 
7


(b) Answer the following questions related to the circuit drawn below


Calculate the current passing through the circuit when:
Switch K1 isclosed
If K1 is closed, it will put both resistors in series, so their resistances are added (5 Ω + 3 Ω = 8Ω)
Given: V = 2V
R = 5 Ω + 3 Ω = 8 Ω
V
Current: I 
R

I 2
5 3
2 0.25A
8

Switches K1 and K2 are bothclosed
When both K1 and K2 are closed, the 5 Ω resistor is short circuited and will not affect the current
I 2 0.67 A
3
Switch K1 is open and K2 isclosed
This will create an open circuit, therefore no current will flow (there is no path for the current to flow around the circuit)

Effects of an electriccurrent
(Not found in exams)

Electricinstallation
Circuit Breaker - An automatically operated electrical switch designed to protect and electrical circuit from damage caused by overload or short circuits
Earthing (E) - A wire that is grounded to the earth
Live (L) - A wire that has a current running through it. They can kill you if you touch them
Neutral (N) -
Fuse - A protective device used to control electric current flowing in a circuit by using an alloy with a very low melting point. It breaks the current when the current is too high

1. Select the best fuse for the following:
(i) Refrigerator rated 250V, 400W Given: P = 400W
V = 250V I = ?
Power Equation: P IV or
I P
V
I 400 1.6 A , therefore a
250
2A fuse is best
(ii) Electric cooker rated 240V, 7.2kW
Given: P = 7.2kW or 7200W V = 240V
I 7200 30 A , therefore a
240
30A fuse is best
(iii) Electric iron rated 240V, 2kW Given: P = 2kW or 2000W
V = 240V
I 2000 8.3A , therefore a
240
10A fuse is best


Cells
Simple Cell - Any kind of battery in which the electrochemical reaction is not reversible (Ex. disposable battery)

Defects of a simple cell - Polarization, local action
Polarization - The process of formation of hydrogen gas around the positive plate of an electric cell. Minimized by using an oxidizing agent called a depolarizer (ex. K2CrO4)
Local Action - When a cell is used up when no external current is flowing as a result of impurities
in the zinc plate. It is minimized by amalgamating zinc plate with mercury
How electromotive force (e.m.f) differs from the potential difference (p.d) of a cell -
Electromotive Force (e.m.f) - Is the potential difference between two terminals of a cell when the cell does not deliver current to an external circuit. The total work done in joules per coulomb of electricity in a circuit where the cell is connected. Measured in volts (V)
Factors determining the size of an induced e.m.f - Number of turns in the coil, strength of the magnet (magnetic field), rate of change of flux (speed of rotation or movement)
Potential Difference (p.d) - Is the potential difference between two terminals of a cell when the cell delivers current to the external circuit. Potential difference is always smaller than the electromotive due to resistance of the cell

FORM FOUR
Waves
Introduction to waves
Frequency - The measurement of a waves cycles per second. Its SI unit is hertz (Hz)
Wavelength - The measurement of the rate at which the phase of a wave moves through space
Velocity (Phase) of a Wave - The fraction of a wave cycle which has happened over a given period of time
Period of a Wave - The duration of one cycle of a wave
Types of Waves - Stationary, longitudinal, mechanical, transverse
Stationary (Standing) Wave - A wave that remains in a constant position due to interference between two waves (ex resonance)
Longitudinal Waves - Waves that have the same direction of vibration along their direction of travel (the vibration of the medium is in the same or opposite direction as the motion of the wave)
Mechanical Waves - Waves which travel through materials (ex vibrating string, sound, seismic waves)
Transverse Waves -
Frequency of a wave: f 1
T
Velocity of a wave: v f

Behaviour ofwaves
Interference - The superposition of two or more waves resulting in a new wave pattern (when two or more waves collide they create a new pattern, called an interference pattern)
Diffraction - Is the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Diffraction occurs with all types of waves

Propagation ofwaves
1. A certain wave has a period of 0.2 sec and a wavelength of 60cm. What is the velocity of the wave in cm/s?
Given: Period of the wave, T = 0.2s Wavelength, λ = 60cm
Frequency, f = ? Velocity, v = ?
Frequency of a wave: f 1
T
Velocity of a wave: v f

Step 1: Solve for frequency (f)
f 1
T
Step 2: Solve for velocity (v)
v f
v 5 60 300cm / s




Soundwaves
Audibility Range - The range of sound waves which can be heard by an organism
Beats - Volume fluctuations due to the interference between sounds of different frequencies
Reverberation - The persistence of sound in a particular space after the original sound is removed, it is caused when a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air
Echo - A reflection of sound
A telephone earpiece converts electric currents into sound waves

Musicalsound
Pitch - The perceived frequency of a sound
Loudness - The quality of a sound that is correlated to amplitude (the physical strength of a wave), which is heard by an organism and is measured in terms of a scale from quiet to loud
Node - A point where the amplitude of a standing wave is minimum
Anti-node - A point where the amplitude of a standing wave is maximum
Fundamental (Frequency) Note - The lowest frequency or note in a harmonic series
Harmonic Series - A series of notes which are formed on a string that travel in both directions along the string, reinforcing and canceling each other to form standing waves creating audible sound waves
Overtones - A frequency higher than the fundamental frequency of a sound
Resonance-Thetendencyofasystemtooscillatewithlargeramplitudeatsomefrequenciesthanatothers
Oscillation-Therepetitivevariationovertimeaboutacentralpointofequilibrium(expendulum,ACpower)
Amplitude - The magnitude of change in the oscillating variable with each oscillation within an oscillating system

Electromagnetic spectrum
Electromagnetic Spectrum - The range of all possible frequencies of electromagnetic radiation
Types of Radiation - Ultraviolet, x-rays, gamma rays, infrared rays, visible light, beta particles, alpha particles
UV (Ultraviolet) Rays - A form of electromagnetic radiation which is shorter than visible light, but longer than X-rays
X-rays - A form of electromagnetic radiation which is shorter in wavelength than UV rays and longer than gamma rays
Gamma Rays - A type of electromagnetic radiation of very high frequency (short wavelength) which are produced by subatomic particle interactions like radioactive decay. Can be used to kill cancer cells
Infrared Rays - A form of electromagnetic radiation which is longer than visible light
Visible Light - The portion of the electromagnetic spectrum that is visible to the human eye
Beta particles - High energy, high speed electrons or positrons emitted by certain types of radioactive nuclei
Alpha Particles - Consist of two protons and two neutrons bound together into a particle identical to a helium nucleus which is produced in the process of radioactive decay
Uses of electromagnetic radiation -
1. A mixed beam of α-particles, β-particles, and γ-rays enter a magnetic field at right angles to the direction of the beam. Draw the diagram which best represents the paths taken by the particles.


Applications of electromagnetic waves in dailylife

Electromagnetism

Magnetic fields due to a current-carryingconductor
How an electric current creates a magnetic field -
Draw magnetic line patterns around a current

Electromagnetic induction
Electromagnetic Induction - A process where an e.m.f is induced in a coil which is interacting with a magnetic field whenever the flux through the coil changes
Applications of electromagnets - Laws of electromagnetic induction -
Faradays Law - Whenever there is a change in the magnetic flux linked with a circuit an electromotive force (e.m.f) is induced, the strength of which is proportional to the rate of change of the flux linked with the circuit
Lenz’s Law - The direction of induced current is always such that it opposes the change producing it Magnetic Flux - A measure of the strength of a magnetic field on one side of a magnet. Its SI unit is V/sec Inductor - A coil of low resistance wire used to store magnetic flux and control an alternating current (AC) Eddy Current - Induced current loops circulating within a conductor
Advantages of eddy currents - Useful in heating metals, electrical damping, crack detection, measurement of thickness of the material or coating, measurement of conductivity
How eddy currents are produced - Produced when flux through a piece of metal changes, it induces an e.m.f. This induced e.m.f causes currents to flow around the metal piece in closed loops. The current is significant because the resistance of the path is very low
How to minimize eddy currents - Using laminated cores, using magnetic materials with high resistivity
Solenoid - A long thin loop of wire wrapped around a metallic core which produces a magnetic field when an electric current is passed through it. They are used as electromagnets
Self Induction - The induction of a magnetic field by its own current
Mutual Induction - The induction of a magnetic field by current in another circuit
Factors affecting the magnitude of an induced e.m.f in a moving coil - Strength of the magnetic field, speed of rotation of the coil
Transformer - A device which transfers electrical energy from one circuit to anther through the transformer’s coils
Reason why high voltage is used for commercial transmission of electrical energy - It minimizes energy losses because high voltage provides lower current. From the equation Power = I2R, so the lower the current, the lower the power losses

NS
Transformer principle:
NP
ES
EP


1. The figure shows a model of an electrical transmission system. AB and CD each represent a long length of cable each having a resistance of 4Ω. The current in AB is 0.1 A, find the:
Power lost by AB andCD
Note that since AB and CD have the same resistance, so they will have the same current
Given: I = 0.1 R = 4Ω
P = ?
Power lost due to resistance: P I 2R

Step 1: Solve for P
P I 2R
P (0.1)24
P 0.04W
Step 2: Calculate total power lost. Note that you need to multiply the power lost by two because we are considering AB and CD, each one lost 0.04W
Total 0.04 2 0.08W

P.d acrossBD

Given: NS = 10 NP =1
EP = 10 ES =?
NS
Transformer principle:
NP


ES
EP

Step 1: Rearrange for ES
E NS E
S N P
P
Step 2: Solve for ES
E 10 10 100V
S 1
Step 3: Solve for ECD
(????)Explain this question better, why is ES = EAC, what do the variables mean?
NECTA 2007 10bii


Current through thebulbGiven: NP =10
NS = 1
IP = 0.1 IS = ?

NS
Transformer principle:
NP
IP
IS


Step 1: Rearrange for IS
I NP I
S N P
S
Step 2: Solve for IS
I 100.11.0A
S 1


Radioactivity
The nucleus of anatom
Protons - Positively charged particles of an atom which have a mass equal to that of a hydrogen atom
Neutrons - Particles of an atom with an equal mass to protons that carry no charge
Electron - A particle which carries a negative charge, it is smaller than protons and neutrons
Radiation - A process in which energetic particles or waves travel through a medium or space

Naturalradioactivity
Naturally occurring forms of radiation - Alpha particles (α-particles), beta particles (β-particles), gamma rays (γ-rays)
α-particles - Particles with low penetrating power which can be stopped by very thin aluminum foil, normal paper or by the human skin. They also have a limited range in the air because the ionize air
β-particles - Particles with high penetration power which can penetrate many metals (or only a few cm of lead), can penetrate human tissue. They can travel long distances in air because they do not ionize air
γ-rays - Rays with very high penetrating power (higher than β-particles) which can penetrate many metals (or only a few cm of lead) and can penetrate human tissue. They can travel very far in the air because they do not ionize air
Half Life - The time required for half of the present number of atoms to decay
Ionizing Radiation - Consists of subatomic particles or electromagnetic waves which are energetic enough to detach electrons from atoms or molecules, thus ionizing them
Geiger-Mullar Counter - A particle detector that measures ionizing radiation

Differentiate between beta (β) particles and gamma (γ) rays -
β-particles
γ-rays

Deflected by electric and magneticfields
Penetrates a few centimeters of an aluminum sheet
Is anelectron
It has mass
Not deflected by electric or magnetic fields
Penetrates a few centimeters oflead
Is electromagneticradiation
Has nomass


A radioactive element has an initial count rate of 1200 counts per minute measured by a scale and this falls to 150 counts per minute in 15hours.
Determine the half life of the elementGiven: Co = 1200 counts per minuteC = 150 counts perminute
t = 15 hours
n = number of half lives = ? t1/2 = ?
Calculating number of half lives: C Co
2n
t
Calculating length of half life: t1 / 2 n

Step 1: Rearrange for 2n
2 nCo
C
Step 2: Solve for n
2n 1200
150
2n8
n = 3
Step 3: Solve for half life time
t t
1/2 n
t 15 5h
1/2 3

The half life of the element is 5 hours

If the initial number of atoms in another sample of this element is 3.0x1020, how many atoms will have decayed in 25hours?

Given: Initial number of atoms, No = 3.0x1020atoms Time, t = 25 hours
Length of half life, t1/2 = 5 hours Number of half lives, n = ?
Number of atoms decayed, N = ?
Calculating length of half life: t1 / 2 n
No

Calculating number of half lives: N 
2n

Step 1: Calculate n
t t
1/2 n
5 25
n
n = 5
Step 2: Calculate N (number of atoms decayed)
N  No
2n
3.0 1020
N 
25
N = 9.375 x 1018atoms


Thorium disintegrates in the followingmanner

232
90
88
Ra228
89
Ac228
228
90
88
Ra 224

State the particles being emitted at each part of the disintegration

Step 1 - Emits an α-particle

232
90
Ra 2284

Step 2 - Emits a β-particle

228
88
 Ac 2280

Step 3 - Emits a β-particle

228
89
Th 228
0

Step 4 - Emits an α-particle

228
90
Ra 2244

Final Equation
Th232
Ra228
Ac228
Th228

Ra 224


(ii) Draw the graph of count rate against time for the following data, then determine the half life of thorium
Time (mins)
0
4
8
12
16
20

Count Rate
40
30
20
14
10
7


By looking at the graph we can see that the half life of thorium is 8 minutes. Since the original count was 40, we look at 20 to see at what time it occurs. Since it occurs at 8 minutes, the half life of thorium is 8 minutes. This is shown by the dotted lines

Artificialradioactivity
Differentiate between natural and artificial radioactivity - Natural radioactivity happens due to the properties of the substance causing it to decay over time, whereas artificial radioactivity is caused by the actions of humans adding neutrons to the atoms causing them to become unstable and decay
Applications of artificial radioactivity - Particle accelerators, nuclear power

Radiation hazards andsafety
Precautions when handling radioactive material - Material should be stored in lead casing, package should be labeled appropriately, package should be handled carefully

Nuclear fission andfusion
Differentiate between nuclear fission and nuclear fusion -
Nuclear Fission - A process whereby a large atomic nucleus is split into two smaller particles, releasing energy and radiation
Nuclear Fusion - The process in which two or more atomic nuclei join together to form a single heavier nucleus
Applications of nuclear fission - Nuclear power, research, nuclear bombs
Applications of nuclear fusion - Hydrogen bombs

Thermionicemission
Cathode rays
Thermionic Emission - A process in which electrons gain sufficient enough energy to overcome the work function of the metal and are able to escape from the surface of the metal
Cathode Ray - A stream of electrons in vacuum tubes (evacuated glass tubes)
Properties of cathode rays - Produce fluorescence, are deflected by electric and magnetic fields, travel in straight lines, carry negative charge, posses kinetic energy

Cathode Ray Oscilloscope (CRO) -
Uses of CRO - Measuring frequencies, measuring voltages, measuring phase differences, measuring small time intervals
Main parts of a CRO - Electron gun, deflection system, fluorescent screen
How a stream of electrons is produced in a CRO - They are released from the cathode by thermionic emission, then they are accelerated by the anode to a high velocity forming the stream of electrons
Ensuring electrons produced do not accumulate at the source - The device uses anodes to accelerate the protons
Ensuring electrons reach their range undeviated - A focusing anode is used
Ensuring electrons travel without meeting other particles on their way to the target - The devices are evacuated so that the electrons do not collide with other particles
Cathode Ray Tube (CRT) -
Cathode Rays - Streams of electrons inside an evacuated CRT
Uses of a cathode ray tube - Television
Why cathode ray tubes are evacuated - So that electrons can travel without colliding with other molecules
Effects when gas is maintained in a CRT - It will behave like an open circuit and when the potential difference (p.d) is strong enough, it will cause an electric spark. Also, an image will not be formed because cathode rays will not be present
Role of high voltage - Provides high tension between electrodes which is used for acceleration of electrons
Role of low voltage - To heat up the cathode
Role of tungsten target - Used to absorb highly energetic electrons and to emit X-rays by converting kinetic energy of the electrons into electromagnetic waves
X-rays
X-rays -
Properties of X-rays - Travel in straight lines at the speed of light, cannot be deflected by electric or magnetic fields, can produce fluorescence, affect photographic film, penetrate matter (dependent on density of the matter), ionize gases, are diffracted by crystals
Effects of X-rays on humans - Destroys body cells, causes mutation of DNA, can cause cancer, can destroy fertility
How to produce X-rays - An accelerated electron beam is focused onto a target with a high melting point. The fast moving electrons collide with the targets atoms and excite them. This causes the electrons of the atoms to go to higher energy levels and jump back to lower energy levels, emitting X-rays (photons)
Types of X-Rays - Hard, soft
Hard X-Ray - An X-ray which can penetrate solid objects
How hard X-rays are produced - Produced when a very high voltage is applied between electrodes which accelerates electrons which release X-rays when they hit the tungsten target
Soft X-Ray - Ax X-ray which cannot penetrate solid objects
Differentiate between X-rays and gamma (γ) rays -
X-rays
Gamma Rays

Caused by energy transitions in electrons
Material used to produce X-rays does notdecay
Wavelength of X-rays is determined by the nature of the target material and voltage (varying strength)
X-rays are emitted by stable atoms of heavy nuclei when hit by fast moving electrons
Caused by nuclear reactions in thenucleus
Material sued to produce gamma raysdecays
Gamma rays depend upon the nucleus of the material for theirwavelength
Gamma rays are produced only when newly formed nuclei are energetically unstable (the stability is gained by emitting gammarays)


Differentiate between X-rays and white light -
X-rays
White light

Cannot be detected by the human eye
Range of frequencies isvariable
Highlypenetrative
Can be detected by the humaneye
Has a fixed range offrequencies
Can only penetrate transparent and translucent matter


Electronics
Semiconductors
Semiconductor - A material with electric conductivity due to electron flow which is an intermediate in magnitude between a conductor and an insulator
Semiconductors commonly used in electronics - Silicon, germanium
Doping (of Semiconductors) - Adding small amounts of impurities to semiconductors to improve their conductivity
P-Type Semiconductor - A type of semiconductor which is obtained through doping which increase the number of positive charge carriers
N-Type Semiconductor - A type of semiconductor where atoms are capable of providing extra conduction electrons to the host material which creates an excess of negative electron charge carriers
P-Type Doping - Creates an abundance of electron holes which allows atoms to accept electrons from a neighbouring atoms covalent bond
Extrinsic Semiconductor - A semiconductor which has been doped giving it different electrical properties than an intrinsic (pure) semiconductor
Intrinsic (Pure) Semiconductor - A semiconductor which has not been doped and therefore has the natural electrical properties of the semiconductor
Electron Hole - Is the concept of the lack of an electron at a position where one could exist in an atom
Differentiate between conductors and semiconductors -







Diodes
Diode - A two terminal electronic component that conducts electric current in only one direction
Junction Diode -
How a junction diode works - Relies on the fact that current flows easily from P-type to N-type diodes.
When P-type is connected to the anode it attracts electrons from the N-type, while the N-type attracts holes from P-type which closes the depletion layer. In the reverse direction the depletion layer will be widened
Rectification - The process of converting an alternating current into a direct current
Role a capacitor plays when used in - AC circuits, DC circuits
AC Circuits - Used in amplifiers for separating AC from DC, in radios for tuning, and in rectification for smoothening
DC Circuits - Charge storage when charging or discharging. When discharging a capacitor can act as an e.m.f source

Transistors
Transistor - A semiconductor device which is used for the amplification of current and voltage
N-type Transistor - P-type Transistor -
Principle of a transistor - It is made of two pieces of either N-type or P-type material with the other type in between them. The outer pieces are used as a collector and emitter while the middle piece is used as the base and is thinner than the outer pieces. During operation a small current is passed from the base to the emitter or its reverse. This small current starts a larger current from the collector to the emitter through the base or itsreverse
Differentiate between NPN and PNP transistors -
PNP transistors
NPN transistors

Consist of a N-type base between two P- type semiconductors
Slower than NPN because holes are slower than electrons
Holes are the majority chargecarriers
Collector and base are negative with respect to theemitter
Consist of a P-type base between two N- type semiconductors
Are faster than PNP so they are used more often
Electrons are the majority chargecarriers
The collector is positive with respect to both the emitter and to thebase


Single stageamplifier
Elementaryastronomy
Introduction toastronomy
Astronomy - The scientific study of the objects in the universe like stars, galaxies, planets and comets Asteroids - A collection of particles of various sizes which revolve around the sun in a way similar to planets Comets - An asteroid which glows brightly in space
Stars - Heavenly bodies which produce their own energy (light and heat)
Planets - Heavenly bodies that cannot produce their own energy and revolve around stars
Meteor - Asteroids that enter into the Earth’s atmosphere and burn up completely before reaching the surface of earth
Meteoroid - Solid object moving in interplanetary space and is smaller than an asteroid
Lunar Eclipse - Occurs when the moon passes behind the earth such that the earth blocks the sun’s rays from striking the moon
Galaxy - A massive gravitationally bound system of stars and gases. Our galaxy is the Milky Way

Solarsystem
Differentiate between a star and a planet - A star is capable of emits its own energy through the fusion of hydrogen atoms, a planet creates energy internally through geothermic actions
Solar System - A system consisting of the sun and all of the astronomical objects bound to it by gravity
Gravity - The force of attraction that causes bodies to fall towards heavier bodies like planets or stars. This is the force that causes planets to revolve around the sun
Heliocentric Theory - The sun is at the centre of the solar system and all other bodies including the Earth revolve around it in circular orbits while rotating about their axes. This is a true theory
Geocentric Theory - Claims that the Earth is at the center of the solar system and the sun and other planets revolve around Earth. This is not a true theory
Basic trends of the planets -
Average temperature of the planets - Average temperature decreases as distance from the sun increases because they are further away from the heat source (sun)
Average densities of the planets - Densities generally decrease from Mercury to Saturn and then increase from Saturn to Neptune. Earth has the highest density because its core is made of iron and nickel, while Saturn has the lowest density because it is made of gases
Length of revolutions of the planets - Period of revolutions increases as distance from the sun increases
Why an astronaut…
Needs a spacesuit to prevent his blood from boiling - The body temperature of the astronaut is enough to boil his blood because there is nearly zero atmospheric pressure
Floats without falling - There is almost no gravitational force so he does not fall towards anything
Uses jets of gas to move instead of swimming like in water - He cannot swim because there is no matter to push against, in order to move forward he needs to exert a force on surrounding matter
Mercuryhas no atmosphere and is the closest planet to the sun
Neptuneis the farthest planet from the sun (Note that Pluto is no longer considered a planet)
Marsis the closest planet to the Earth Saturnis surrounded by rings
Jupiteris the largest planet in the solar system

Venusis the brightest planet in the solar system

Constellations
Constellation - A certain area in the celestial sphere that can be used for navigation based on the perceived pattern formed by prominent stars in the night sky

The earth and themoon
Tides - The rise and fall of sea levels caused by the effects of gravitational forces by the moon, sun and the rotation of the earth
Mass and weight on the Earth and Moon - Mass never changes since it is not affected by gravity (it will be the same on the Moon and on Earth. Weight will change because weight is affected by gravity (it will be heavier on Earth and lighter on the Moon)

1. The distances of Jupiter from the sun 7.8 x 108km and one year on Jupiter is equivalent to 12 years on earth. Calculate the:
Distance of its path in oneyear
Given: Radius of the path, 7.8 x 108km Circumference of a circle: C 2r
Note that the distance of its path is the circumference of a circle, since Jupiter has a circular orbit

Step 1: Calculate circumference
C 2r
C 2 (7.8 108)
C 4.903 109km

Speed of the planet in km per hour Given: Distance = 4.903 x109km
Time = 12 years x 365 days x 24 hours = 105,120 hours
Distance

Speed: Speed 


Time

Step 1: Calculate speed
Speed Distance
Time
4.903109
Speed 
105,120



46,641km / hr


4.7.0 Geophysics
(Found in the Geography study guide)