1. Thermal Physics

2. Temperature and Heat
Temperature – a measure of hotness or coldness of an object
Heat - Energy Transfer

3. Kinetic Theory Strong forces of attraction between the particles
Higher temperature = more kinetic energy
Strong forces of attraction between the particles
No forces of attraction between the particles

4. Internal Energy
“…of an object is the sum of the random distribution of the kinetic and potential energies of its molecules”
The energy due to the individual movements and arrangement of molecules in a material.
Thermal energy is the part due to their temperature,
but some internal energy may be due to other causes, such as magnetic interaction between molecules, so a magnetised iron bar has more internal energy than one that isn’t.

5. How can the internal energy of a substance be changed?
In what situations would there be no change in the internal energy of a substance?

6. Internal energy can be changed by:
Heat transfer, or energy transfer by radiation
Work done by a force on, or by the object, including work done by electricity, or a gas pushing against a balloon.
If the flows of energy are balanced (or zero), internal energy stays constant.
EG, the internal energy of a filament lamp increases with work done by electricity, but becomes constant at its operating temperature.

7. Absolute Zero
Celsius scale defined by ice point and steam point of water at standard atmospheric pressure.
Absolute (or Kelvin) scale is defined by absolute zero and the triple point of water, K, the temperature where ice, water and water vapour are in thermal equilibrium.
Ice point = K, steam point = K, so oC = K –

9. Specific Heat Capacity
Why do the tiles around a pool heat up in the sun so much more than the water?
Why is water so expensive to heat up?
What factors determine how much a lump of stuff heats up when you transfer energy to it?

10. Molecules undergo many characteristic internal vibrations
Molecules undergo many characteristic internal vibrations. Potential energy stored in these internal degrees of freedom contributes to a sample’s energy content, but not to its temperature. More internal degrees of freedom tend to increase a substance's specific heat capacity, so long as temperatures are high enough to overcome quantum effects.

11. Specific Heat Capacity
The SHC, c of a substance is “the energy needed to raise the temperature of unit mass of the substance by 1K without change of state”
Unit = Jkg-1K-1
Energy needed, E = ΔQ = mcΔT = kg x Jkg-1K-1 x K = J
The Heat Capacity C of an object = mc, measured in JK-1
This is the heat needed to raise its temperature by 1K

12. Water 4200 Jkg-1K-1

13. How could you work out c for water in the lab?
If an electric shower has 9L of water flowing through it per minute, what power rating does your shower need to have?
What will happen to the flow rate in winter if you want the same water temperature?
What rated shower would you need to maintain the same flow rate?

14. How could you work out c for water in the lab?
If an electric shower has 9L of water flowing through it per minute, what power rating does your shower need to have?
What will happen to the flow rate in winter if you want the same water temperature?
What rated shower would you need to maintain the same flow rate?
What current would be needed to supply the shower?

15. What happens when state changes?
Possibly not what you might expect

16. For each of the following, find the internal energy difference for a 10 K change in temperature:
1.5.0 kg of water.
2.The bit of a soldering iron, made from 3.5 g of copper.
3.An expanded polystyrene cup (EPS) of mass 5.0 g.
4.A steel brake disc of mass 1.5 kg.
5.If you eat a fruit pastry fresh from a hot oven, the pastry may be harmless while the fruit filling scalds your tongue.
Use your ideas about specific heat capacity to explain why.
Material
Specific heat capacity /
J kg–1 K– 1 Al
900 Cu
385
EPS
1300 Fe
450
Ice
2100
Air
1000
Water
4200

17. Because of state change m c ΔT isn’t enough
E = m L
L is specific latent heat of fusion/vaporisation
Units= Jkg-1
Change of state
AT CONSTANT TEMPERATURE

18. Q = m L
Q = m c ΔT
Q = m c ΔT
Q = m L
Q = m c ΔT
Both L and c are material and not object specific quantities, much more useful.

19. Lets look at heat moving (thermal transfer or energy)

20. Thermal transfer of energy
Conduction
Transferred directly within a material
ΔT across material is the driving force
Convection
Transport by bulk movement
Density, buoyancy, currents
Free and forced, Newton, T or T5/4
Radiation
By means of electromagnetic waves
The black body
Stephan

21. Some more terms
Internal energy: Potential energy in bonds and KE of particle motion (ΔU) Adiabatic: No heat transfer (ΔQ=0) Isothermal: You guessed it (ΔT=0) Now, lets go...