Physics form three topic five

 Thermal EnergyThe Concept of HeatExplain the concept of heatHeat – Is the transfer of energy due to temperature differences.Temperature – Is the degree of hotness or coldness of a body.Or heat is a form of energy which raises the temperature of the substance.SI Unit of Temperature is Kelvin (K).Conversion of centigrade into fahrerinheit given by:f = 9/5ºC + 32Conversion

of Fahrenheit into centigrade given by C = 5/9/ ( F – 32). Thermometer
used for measurement of temperature. Maximum thermometer is the one
which is used to measure the highest temperature obviously filled with
mercury.A
Minimum thermometer is used to measure the lowest temperature and it is
filled with alcohol. Combined maximum and minimum thermometer (Six’s
thermometer) is used to measure highest and lowest temperature at the
same time.SI Unit of Heat is Joule (J) mathematically heat energy given by:

• H = MC (Q2 – Q1)
• M = Mass of substance
• C = Specific heat capacity
• Q2 = Final Temperature
• Q1 = Initial Temperature

Source of Thermal Energy in Everyday LifeState the source of thermal energy in everyday lifeThere
are numerous sources of energy such as the sun, fuels, nuclear sources,
geothermal, electricity among others. The most important source of
thermal energy is the sun. The sun generates its energy by a process
called thermonuclear fusion. Most sources of thermal energy derive their
energy from the sun. Thermal energy from the sun makes life on earth
possible.Difference between Heat and TemperatureDistinguish between heat and temperatureHeatandtemperatureare related and often confused. More heat usually means a higher temperature.Heat(symbol:Q)
is energy. It is the total amount of energy (both kinetic and
potential) possessed by the molecules in a piece of matter. Heat is
measured in Joules.Temperature(symbol:T)
is not energy. It relates to the average (kinetic) energy of
microscopic motions of a single particle in the system per degree of
freedom. It is measured inKelvin (K), Celsius (C) or Fahrenheit (F).When
you heat a substance, either of two things can happen: the temperature
of the substance can rise or thestateof substance can change.

Heat	Temperature
Definition	Heat is energy that is transferred from one body to another as the resultof a difference in temperature.	Temperature is a measure of hotness or coldness expressed in terms of any of several arbitrary scales like Celsius and Fahrenheit.
Symbol	Q	T
Unit	Joules	Kelvin, Celsius or Fahrenheit
SI unit	Joule	Kelvin
Particles	Heat is a measure of how many atoms there are in a substance multiplied by how much energy each atom possesses.	Temperature is related to how fast the atoms within a substance are moving. The ‘temperature’ of an object is like the water level – it determines the direction in which ‘heat’ will flow.
Ability to do work	Heat has the ability to do work.	Temperature can only be used to measure the degree of hea

Thermal Expansion of SolidsExpansion of SolidsDemonstrate expansion of solidsWhen a solid is heated one or more of the following may occur:

• Its temperature may rise
• Its state may change
• It may Expand

Expansion of solids is the increase in dimensions of a solid when heated.Contraction of solids is the decrease in dimensions of a solid when is cooled.DEMONSTRATION OF EXPANSION OF SOLIDSIn order to demonstrate the expansion of solid we can use following method

1. The ball and Ring Experiment
2. The Bar and Gap Experiment

The ball and Ring Experiment1st Case: When the ball is not heated then it will pass through the ring very easily because it has a small volume.

2nd Case: When the ball is heated, it will expand and increase in volume, so itwill not pass through the ring.

The Bar and Gap experiment1stCase:When the Bar not heated (Not raised with temperature) then the dimension will remain constant.2nd Case:When
the Bar is heated (raised with temperature) then the dimension of the
Bar will increase and eventually will not pass thought the Gap.Expansion of Solids in terms of Kinetic Theory of MatterExplain expansion of solids in terms of kinetic theory of matterWhen asolidis
heated, its atoms vibrate faster about their fixed points. The relative
increase in the size of solids when heated is therefore small. Metal
railway tracks have small gaps so that when the sun heats them, the
tracks expand into these gaps and don’t buckle.Forces due toexpansionNormally
Expansion and contraction is accompanied by tremendous forces; The
presence of force indicates the expansion and contraction is Resisted.

Bar breaker

• Consists
  a strong metal blocker with a pair of vertical jaws J and a strong
  metal Bar R. The metal bar has a wing nut N at one end and an eye at the
  other end.
• The bar is placed between the two pair of Jaws
• A short cast iron C is inserted in the eye of the bar.
• The bar is then heated it expands and the wing not screwed to tighten the bar R against the jaws.
• The
  bar is then allowed to cool as it cools, it contracts the short cast
  Iron rod C which presses against the jaws of the bar breaker, Resists
  the contraction of the Metal bar R.
• The resistance to the
  contraction of the bar sets up very large forces which breaks the short
  cast Iron rod C in the eye of metal bar, Because the contracting bar is
  trying to pull itself through the small gap in the frame.

Expansivity of Different SolidsIdentify expansivity of different solidsThe coefficient of linear expansion or linear expansivity (x)The amount by which the linear dimension of a given solid expands depends on:

• The length of the solid
• The temperature to which the solid is heated
• The nature of solid

Coefficient
of linear Expansivity (x) is the fractional increase in length of the
solids per original length per degree rise in temperature.Mathematical formula

Thus

SI Unit of coefficient of linear expansivity (X) is per degree centigrade ºC -1Example 1A
copper rod has a length of 40cm on a day when the temperature of the
room is 22.3ºC. What will be its length become on a day when the
temperature of the room is 30ºC ? The linear expansivity of copper is 0.
000017/ºCSolutionTable which shows the coefficient of Expansivity Constant.

Substance	Linear Expasivity (PerºC)
Aluminum (Al)	0.000026
Brass	0.000019
Copper	0.000017
Iron	0.000012
Steel	0.000012
Concrete	0.000011
Glass	0.0000085
Invar ( Alloy of Iron and Nickel)	0.000001

The Application of Expansion of Solids in Daily LifeExplain the applications of expansion of solids in daily lifeThere
is a large number of important practical applications of thermal
expansion of solids; While laying the railway tracks, a small gap is
left between the successive lengths of the rails. This will allow
expansion during a hot day. The iron tyre is to be put on a wheel, the
tyre is first heated until its diameter becomes more than that of the
wheel and is then slipped over the wheel.Thermal Expansion of LiquidsThe Apparent Expansion of LiquidsExplain the apparent expansion of liquidsLiquids
expands when heated and contracts when cooled. It is easier to observe
expansion in liquids than in solids. Different liquids expand at
different rates in response to the same temperature change. Liquids
expand much more than solids for equal changes of temperature. Apparent
expansion of liquids is always less than the true expansion of the
liquid.Demonstrate the Effects of Heat on LiquidsDemonstrate the effect of heat on liquidsLiquids
unlike solids can be poured. If a liquid is poured into a vessel, it
takes the shape of the vessel. For this reason a liquid can’t have
linear and aerial expansivity, thus liquids have only volume
expansivity. Liquids molecules have kinetic energy. This energy
increases if the temperature of the liquid is raised by heating. Heating
causes the molecules of liquid to move faster.Activity 1Items Needed

• Large heat safe glass bowl
• Cooking Oil
• Food Coloring
• Two 2×4 blocks
• Candle
• Match or Lighter

Instructions

1. Begin by filling a large glass bowl with cooking oil.
2. Next, add between 5-10 drops of food coloring into the oil. Helpful Tip: Place the drops near the center of the bowl.
3. Prop the bowl up off the table using two 2×4 blocks.
4. Light a candle and carefully place it under the bowl. The flame of the candle should touch the bottom of the glass bowl.
5. Look
   through the side of the glass bowl and watch carefully to observe what
   happens. Helpful Tip: It will likely take 5 minutes before you see
   anything happen to the liquid/food coloring.

You can alternatively follow the experiment through the following vedioVerification of Anomalous of WaterVerify the anomalous expansion of waterThe
instrument used to demonstrate anomalous expansion of water is called
hope’s apparatus. it consists of a brass cylinder, jacket J with a
mixture of ice and salt and two thermometers A and B at regular
intervals upward and at the bottom.The hope’s experiment shows that
water contracts as it cools down to 4 degree centigrade and then expands
as it cooled further below 4 degree centigrade.In
the year 1805, the scientist T. C. Hope devised a simple arrangement,
known as Hope’s apparatus, to demonstrate the anomalous behaviour of
water.

Hope’s
apparatus consists of a long cylindrical jar with two openings on the
side, one near the top and the other near the bottom to fit thermometers
in each of these openings. A metallic cylindrical air-tight trough with
an outlet is also fitted onto the jar, on its central portion. Two
thermometers are fitted air-tight in the two openings of the cylindrical
jar. The thermometer near the bottom of the jar is T1, and the one near the top of the jar is T2.
Now the cylindrical jar is filled with water. The cylindrical trough at
the central portion of the jar is filled with a freezing mixture of ice
and common salt.The Application of Expansion of Liquids in Everyday LifeExplain the applications of expansion of liquids in everyday lifeWater
in lakes and ponds usually freezes in winter. Ice, being less dense
floats on the water. This insulates the water below against heat loss to
the cold air above. Water at 4 degree centigrade being most dense,
remains at the bottom of the lake, while ice, being less dense than
water floats on the layers of water. This enables aquatic animals to
survive in the water below the ice.Thermal Expansion of GasesThe Concept of Thermal Expansion of GasesExplain the concept of thermal expansion of gasesGases
expand when heated just like solids and liquids. This is because the
average kinetic energy of the molecules in a gas is directly
proportional to the absolute temperature of the gas. Heating the gas
increases the kinetic energy of its molecules, making them vibrate more
vigorously and occupy more space.The Relationship between Volume and Temperature of Fixed Mass of Air at Constant PressureInvestigate the relationship between volume and temperature of fixed mass of air at constant pressureThree
properties are important when studying the expansion of gases. These
are; pressure, volume and temperature. Charles law states that the
volume of a fixed mass of gas is directly proportional to the absolute
(Kelvin) temperature provided the pressure remains constant.
Mathematically V1T2 = V2T1.Example 2the
volume of gas at the start is recorded as 30 cm3with a temperature of
30°C. The cylinder is heated further till the thermometer records 60°C.
What is the volume of gas?Solution:We know,V/T = constanttherefore,V1/T1=V2/T2V1 =30 cm3T1 =30°C = 30+273 = 303K(remember to convert from Celsius to Kelvin)T2 =60°C = 60+273 = 333KV2 =?V1/T1=V2/T2V2=V1xT2/T1V2=30×333/303= 32.97 cm3The Relationship between Pressure and Volume of a Fixed Mass of Air at Constant TemperatureInvestigate the relationship between pressure and volume of a fixed mass of air at constant temperatureThe
relationship obtained when the temperature of a gas is held constant
while the volume and pressure are varied is known as Boyle’s law.
Mathematically, P1V1 = P2V2. Boyle’s law states that the volume of a
fixed mass of gas is inversely proportional to its pressure if the
temperature is kept constant.PressurexVolume = constantpxV = constantExample 3The volume of gas at the start is 50 cm3with a pressure of 1.2 x 105Pascals. The piston is pushed slowly into the syringe until the pressure on the gauge reads 2.0 x 105Pascals. What is the volume of gas?Solution:We knowp x V = constanttherefore,p1xV1= p2xV2p1=1.2 x 105PascalsV1=50 cm3p2=2.0 x 105PascalsV2=?p1xV1= p2xV2V2=p1xV1/p2V2=1.2×105x50/2.0 x 105V2= 30 cm3The Relationship between Pressure and Temperature of a Fixed Mass of Air at Constant VolumeInvestigate the relationship between pressure and temperature of a fixed mass of air at constant volumeTo
investigate the relationship between the pressure and the temperature
of a fixed mass, the volume of the gas is kept constant. The pressure is
then measured as the temperature is varied. P1/T1 = P2/T2 ,this is
called pressure law. The pressure law states that the pressure of a
fixed mass of a gas is directly proportional to the absolute temperature
if the volume is kept constantExample 4Pressure of gas is recorded as 1.0 x 105N/m2at a temperature of 0°C. The cylinder is heated further till the thermometer records 150°C. What is the pressure of the gas?Solution:We know,p/T = constanttherefore,p1/T1= p2/T2p1=1.0 x 105N/m2T1=0°C = 0+273 = 273K(remember to convert from Celsius to Kelvin)T2=150°C = 150+273 = 423Kp2 =?p1/T1= p2/T2p2=p1xT2/T1p2=1.0×105x423/273= 1.54 x 105N/m2The General Gas Equation from the Gas LawsIdentify the general gas equation from the gas lawsThe three gas laws give the following equations:

1. pV = constant(when T is kept constant)
2. V/T = constant(when p is kept constant)
3. P/T= constant(when V is kept constant)

These 3 equations are combined to give the ideal gas equation:

Where,

• p = the pressure of the gas
• V = the volume the gas occupies
• T = the gas temperature on the Kelvin scale

From
this equation we know that if a fix mass of gas has starting values of
p1, V1 and T1, and then some time later has value p2, V2 and T2, the
equation can be written as:

Exercise 1Sabah
pumps up her front bicycle tyre to 1.7 x 105Pa. The volume of air in
the tyre at this pressure is 300 cm3. She takes her bike for a long ride
during which the temperature of the air in the tyre increases from 20°C
to 30°C. Calculate the new front tyre pressure assuming the tyre had no
leaks and so the volume remained constant?Absolute Scale of TemperatureExplain absolute scale of temperatureAbsolute
zero is the lowest temperature that can be attained theoretically. It
is not possible to attain this temperature because all gases liquefy
before attaining it. The kelvin scale of temperature is obtained by
shifting the vertical axis to -273 degrees Celsius and renaming it 0 K.
On the scale 0 degrees Celsius becomes 273 K and 100 degrees Celsius
corresponds with 373 K.Convertion of Temperature in Degrees Centigrade (Celsius) to KelvinConvert temperature in degrees centigrade (celsius) to kelvinThe
Kelvin temperature scale takes its name after Lord Kelvin who developed
it in the mid 1800s. It takes absolute zero as the starting point and
temperature measurements are given the symbol K (which stands for
“Kelvin”). Temperature differences on the Kelvin scale are no different
to those on the Celsius (°C) scale. The two scales differ in their
starting points. Thus, 0°C is 273K.Converting from Celsius to Kelvin

• Temperature in °C + 273 = Temperature in K

Converting from Kelvin to Celsius

• Temperature in K – 273 = Temperature in °C

Example 5The temperature of a gas is 65 degrees Celsius. Change it to the kelvin scale.SolutionT(K) = degrees Celsius + 273, T(K) = 65+273therefore T(K) = 338 K.Standard Temperature and Pressure (S.T.P)Explain standard temperature and pressure (S.T.P)The
standard temperature and pressure (S.T.P) is a set of conditions for
experimental measurements to enable comparisons to be made between sets
of data. The standard temperature is 0 degrees Celsius (273 K) while the
standard pressure is 1 atmosphere (101300 Pa or 760 mm of mercury).Expansion of Gas in Daily LifeApply expansion of gas in daily lifeLand
and sea breezes are the result of expansion of air caused by unequal
heating and cooling of adjacent land and sea surfaces. The piston engine
and firing bullets from guns work under principles of expansion of
gases.

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