Heat and Temperature Flashcards Preview

Physics Foundations > Heat and Temperature > Flashcards

Flashcards in Heat and Temperature Deck (29)
Loading flashcards...
1
Q

What does it mean if a variable is intensive/extensive?

A

Intensive - independent of the scale of the system.

Extensive - scales with the system

2
Q

What is a open/closed system?

A

Open - can exchange energy and mass with its surroundings

Closed - can exchange only energy with its surroundings

3
Q

What are adiabatic/diathermal walls?

A

Adiabatic - prevent heat transfer.

Diathermal - all heat transfer.

4
Q

What does isothermal mean?

A

At constant temperature.

5
Q

What does isochoric mean?

A

Constant volume.

6
Q

What does isobaric mean?

A

Constant pressure.

7
Q

What does adiabatic mean?

A

No heat flow or a sudden process (before heat flow can occur).

8
Q

What is Le Chatelier’s Principle?

A

A system in equilibrium reacts to a small change in one of its variables by changing its internal conditions to reverse the change. (stay in equilibrium)

9
Q

What is the definition of thermal equilibrium?

A

Two systems are in thermal equilibrium if their state variables do not change when they are put in contact via a diathermal wall.

10
Q

State the 0th Law of Thermodynamics.

A

Two systems are in thermal equilibrium if, and only if, they have the same temperature.

11
Q

What is the internal energy of a system?

A

The sum of the translational, vibrational and rotational energies of it’s components.

12
Q

How do you know if something is a thermometer?

A

If it has an observable property which changes with temperature.

13
Q

What is the ice point?

A

Liquid and solid water in thermal equilibrium at 1 atmosphere. (0 degrees C)

14
Q

What is the steam point?

A

Liquid and vapour water at thermal equilibrium at 1 atmosphere (100 degrees C)

15
Q

How do gas thermometers work?

A

They use one reference point - absolute zero - 273 degrees C or 0K.

16
Q

What is the equation for linear thermal expansion?

A

α = 1/L0 * ΔL/ΔT, where L0 is the value of the dimension at some initial T0.

17
Q

How would you calculate length using the equation for linear thermal expansion?

A

L = L0 + ΔL = L0 + αL0ΔT

18
Q

What does the graph look like for potential energy between two atoms bound in a solid?

A

Goes from positive to negative and then tends to zero (u shape). Higher temp = wider curve.

19
Q

What is the equation for volume thermal expansion?

A

β = 1/V0 * ΔV/ΔT = 3α (since dV = 3L^2 dL)

20
Q

What are the 2 equations for ΔT in terms of heat flow Q?

A

ΔT = Q/nC, where C is the molar heat capacity and n is the number of mole
OR
ΔT = Q/mCm, where Cm is the specific heat capacity

21
Q

What is the specific heat capacity of water?

A

4190 J K^-1 kg^-1

22
Q

What is meant by latent heat?

A

Latent heat is the amount of heat involved in a phase change.

23
Q

What is the equation for heat transfer Q?

A

Q = +/- m*L, where L is the latent heat.

24
Q

How do you draw a phase diagram for p-T? What is the centre point called?

A

Like a diagonal Y shape with curvey lines - solid on left, vapour at bottom and liquid at top. Centre called triple point.

25
Q

On the p-T diagram, what is the line between solid and vapour called?

A

Sublination curve.

26
Q

What happens at the critical point?

A

Separation between liquids and vapour ends - beyond there is a smooth continuous change.

27
Q

What is the equation for heat flow in conduction?

A

dQ/dt = -κA dT/dx, where κ is the thermal conductivity (-ve sign because heat flows from higher to lower temperature.

28
Q

What can cause convection?

A

Local changes of density or temperature which causes heat flow due to motion of fluid.

29
Q

What is the equation for power in radiation?

A

P = eσA*T^4 (Stefan - Bolzmann Law), where e is the emissivity and σ is the Stefan-Boltzmann constant.