Thermal properties of matter
● Solids → closely packed
● Liquids → loosely packed
● Gases → very loosely packed, far apart from each other
● Brownian motion
○ It is a random, zig-zag motion of the particles
○ Smoke in the air, pollen particles dusted into water they move in a random or zig-zag
motion
● Conditions for brownian motion
○ Have to be light particles
○ Medium in which particles are suspended have to move randomly
● How brownian motion occurs
○ Bits of smoke and pollen grains are little in mass hence they are jostled around by air
molecules
○ When they push the smoke molecules randomly, the motion is called Brownian motion
● Internal energy
○ It is the total kinetic and potential energy of the object
● Kinetic energy
○ Higher temperature results in more kinetic energy, directly proportional
● Potential energy
○ Inter-particle space, greater the distance, the more the potential energy. Less distance,
less energy
● Temperature
○ The degree of hotness or coldness of an object
○ S.I unit is Kelvin(K)
○ Measure of average kinetic energy of the individual particles
○ More the temperature, higher the internal and kinetic energy
● Heat energy
○ It is the energy transferred from higher temperature to lower temperature object
○ Temperature and kinetic energy are directly proportional
● Pure ice melts at 0 degree celsius
● Pure water boils at 100 degree celsius
Temperature scales
● Celsius temperature scale
○ Human creation
○ Divides the graduations between the freezing and boiling temperatures of water by 100
○ So water freezes at 0 degree celsius and boils at 100 degree celsius
● Fahrenheit temperature scale
○ Freezing point of water is 32 degree fahrenheit
○ Boiling point of water is 212 degree fahrenheit
● Kelvin temperature scale
○ 100 divisions
○ Lower fixed point (freezing point of water) = 273K
○ Upper fixed point (boiling point of water) = 373K’
● Conversions
○ Fahrenheit(F)
■ F = 9/5 C + 32
■ F = 9/5(K-273) +32
○ Celsius(C)
■ C = 5/9(F-32)
■ C = K - 273
○ Kelvin(K)
■ K = C + 273
■ K = 5/9 (F -32) + 273
Thermometer
● Instrument used to measure the temperature of an object
● Clinical thermometer
○ Range is from 35 to 42 degree celsius
● Laboratory thermometer
○ Range is from -10 to 110 degree celsius
● Liquid in glass thermometer
○ Has a bulb, capillary tube(Bore), and the alcohol and mercury is in the bulb
○ Put it in melting ice and mark as 1 degree
○ After marking the fixed points, there are 100 equal graduations that you
mark
○ Principal → liquid expands on heating and contracts on cooling
○ 0 degree is called ICE point and 100 degree is STEAM point
● Thermistor thermometer
○ It has a prove, digital display and a battery
○ Principal → it is a device which becomes a much better electrical
conductor, when temperature rises
○ This means that the higher current flows from the battery causing
the higher reading on the digital meter
○ Greater the temp, greater the conductivity hence resistance will
reduce
○ The current doesn’t run out as long as there is a battery
● Thermocouple thermometer
○ It has copper wires, constantan, milli ammeter/ voltmeter/ galvanometer, hot and cold
junction
○ On the 2 sides of the junctions the same wire has to be there
○ Difference in temperature between the 2 junctions causes a tiny voltage to form
○ You can measure this voltage using a milli voltmeter as there is less current
○ Cold junction is kept inside the meter and is at constant temperature
○ The hot junction has a probe, the material has to be touched to the probe to measure the
temperature.
○ 2 different metals are joined at the ends to form 2 junctions. One of them forms the hot
junction, the other forms the cold junction. Difference in temperature causes voltage
which makes current flow. The ammeter, voltmeter and galvanometer are calibrated to
read temperature
○ Greater difference, results in greater current and this greater reading
○ Advantages
■ It is robust(won't break easily)
■ They are quick to respond
■ It has a wide range (-200 and 1100 degree)
■ It can be linked to other electrical circuits or computers
Name
Description
Factors affecting it
Sensitivity
Change in length per unit
rise of temperature
→ narrow diameter; ↑
sensitivity
→ larger bulb; ↑ sensitivity
→ liquid with greater
expansivity; ↑ sensitivity
Linearity
Uniform expansion of liquid
per unit rise of temperature
→ linear scale: equal distance
between 2 consecutive
graduations on the
thermometer scale
→ use liquid with uniform
expansion
Responsiveness
How quick the thermometer
responds top change in
temperature
→ thinner the bulb; ↑
responsiveness
→ smaller bulb; ↑
responsiveness
Range
Difference between the
highest and lowest reading
on the thermometer scale
→ larger the bore; ↑ range
● Thermal expansion
○ When materials are heated, they expand
○ This expansion happens because the molecules start to move around(or vibrate) faster,
which causes them to knock into each other and push each other apart
● Thermal expansion in states
○ Solids → expands slightly (due to the strong bonds holding the molecules together)
○ Liquids → Expand more than solids (due to the weaker bonds between the molecules)
○ Gases → expand significantly (due to there being no bonds holding the molecules together)
● Application of thermal expansion
○ It is used in thermometers to measure temperatures
○ A bimetallic strip, consisting of 2 metals that expand at different rates, can be made to
bend at a given temperature, forming a temperature-activated switch
● Consequences of thermal expansion
○ The expansion of solid materials can cause them to buckley if they get too hot
○ This could include - metal railway tracks, road surfaces and bridges
○ Things that are prone to buckling usually have a gap built into them providing some room
for them to expand
Thermal expansion in states
● Solids
○ When a solid is 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.
● Liquids
○ They expand for the same reason, but because the bonds between separate molecules are
usually less tight they expand more than solids.
○ This is the principle behind liquid-in-glass thermometers. An increase in temperature
results in the expansion of the liquid which means it rises up the glass.
● Gases
○ Molecules within gases are further apart and weakly attracted to each other. Heat causes
the molecules to move faster, (heat energy is converted to kinetic energy) which means
that the volume of a gas increases more than the volume of a solid or liquid.
○ However, gases that are contained in a fixed volume cannot expand - and so increases in
temperature result in increases in pressure
● Thermal capacity
○ It is the amount of heat energy required to raise the temperature of that object by 1
degree celsius
○ The greater the thermal capacity of an object, the more heat energy it takes to raise its
temperature
○ The thermal capacity is als equal to the amount of heat energy an object will give out when
it cools by 1 degree celsius
● Energy(E) → Thermal capacity x Temperature(T)
● Thermal capacity → mass(m) x specific heat capacity(c)
● Specific heat capacity
○ The specific heat capacity of a substance in the amount of thermal energy required to
raise the temperature of 1kg of that substance by 1 degree celsius
○ It is measured in joules per kilogram per degree celsius (J/kg°C)
○ Thermal energy and specific heat capacity are directly proportional
● Change in (internal)energy = mass x specific heat capacity x change in temperature
● ΔE = m x c x ΔT
● Specific heat capacity
○ Heat supplied to substance(divided by)mass x change in temperature
Measuring specific heat capacity
● Method
○ Place the immersion heater into the central hole at the top of
the block of substance
○ Place the thermometer into the smaller hole and put a couple
of drops of oil into the hole to make sure the thermometer is
surrounded by hot material
○ Fully insulate the block by wrapping it loosely with cotton
wool/lagging
○ Record the temperature of the block
○ Connect the heater to the power supply and turn it off after
10 minutes
○ After 10 minutes, the temperature will still rise even though
the heater has been turned off and then it will begin to cool.
○ Record the highest temperature that it reaches and calculate
the temperature rise during the experiment
● Analysis
○ Energy transferred = potential difference x current x time
○ E = V x I x t
■ V → Voltmeter reading
■ I → Ammeter reading
■ t → time
○ E = mct
○ C(specific heat capacity) = E/mt
● Control measures
○ Do not touch when switched on. Position away from the edge of the desk. Allow time to
cool before packing away equipment. Run any burn under cold running water for at least 10
minutes
● Latent heat
○ It does not increase the substance's temperature therefore known as latent heat.
○ The word specific means that it is compared to 1kg of the substance
○ Unit → kJ/kg
● Specific latent heat of vaporisation
○ Amount of heat energy required to change the state of unit mass of substance from liquid
to gas at constant temperature
● Specific latent heat of fusion
○ Amount of heat energy required to change the state of unit mass of substance from solid
to liquid at constant temperature
● Energy required = mass x specific latent heat
● E = mLv (latent heat of vaporisation)
● E = mLf (latent heat of fusion)
● Measuring latent heat of fusion of ice
○ Place an insulated container on a balance and record its mass
○ Place about 20g of ice at 0° celsius in the container. Record the reading on the balance
○ Pour about 200g of water into the container. Record the reading on the balance(used to
determine mass of ice and water)
○ Stir the mixture of ice and water, Put the lid in place. Record the temperature of the
mixture.
○ Read the temperature every minute or two. Record the temperature of the water when it
reaches its lowest value (or when it starts to rise)
○ Calculate the decrease in temperature of the water
○ Calculate the energy lost by the water. This is the energy gained by the ice as it metals,
and so you can calculate its specific latent heat (s.h.c of water = 4200J/kgC)
● If you're measurements are lower of higher than expected
○ Lower value than expected, heat is absorbed by the environment.
○ Higher value than expected, heat is given out by the environment.
