Thermal Physics

Question 1

Define absolute zero

Answer 1

? The lowest temperature that is theoretically possible ( at this temperature particles would stop vibrating and exert zero pressure

Question 2

Define Charles law

Answer 2

? Volume is directly proportional to temperature (K) at a constant pressure
V1/T1=V2/T2

Question 3

Define Boyles law

Answer 3

? Pressure is inversely proportional to volume at a constant temperature. (Isothermal Change)
A gas at very high temperatures does not obey this law.

P1V1 = P2V2

Question 4

Define Lussac’s Law

Answer 4

? Pressure is directly proportional to temperature (K) at a constant volume

P1/T1 =P2/T2

Question 5

Define internal energy

Answer 5

? Is the sum of the randomly distributed kinetic energies and potential energies of the particles in a gas.

Question 6

Properties of ideal gases

Answer 6

? Particles have no potential energy

• all collisions are elastic
• point masses
• no change of state

Question 7

Define specific heat capacity

Answer 7

? the energy required to raise the temperature of 1kg of a given substance by 1 Kelvin

Question 8

Equation to calculate S.H.C

Answer 8

Q = mc (change) T

Unit: J/kgK

Question 9

Define specific latent heat

Answer 9

? The energy required to change the state of a 1kg of a substance without a change in temperature.

Question 10

Equation for specific latent heat

Answer 10

E =mL

Units: J/kg

Question 11

Conversion between Kelvin and Celsius

Answer 11

-273 Degrees = 0K

Question 12

What in the kinetic theory

Answer 12

? The molecules of a gas are in a state of constant motion in which the speed and the direction of each molecule is completely random.

Question 13

Assumption of the kinetic theory

Answer 13

• The molecules of a particular gas are identical and in random motion
• The collisions between the molecules and between the walls of the container are perfectly elastic
• The volume of a molecule is negligible, compared to the volume of the container
• There are no intermolecular attraction between the molecules
• The time taken for a collision between two molecules is negligible compared with the time taken for the collisions between a molecule and the wall

Question 14

Steps to derive the equation

Answer 14

1. Find an expression for the change in momentum when the ball collides
2. Find an expression for the force (Δmv/t) from point 1 to point 2
3. Find an expression for the pressure (F/A) due to this force
4. Multiply by N molecules (total number in the container)
5. Substitute Crms for Vx using the equation earlier

Question 15

Equation for ideal gas

Answer 15

PV/T = k

pV =nRT / pV =NkT

Question 16

Can you explain why the temperature of a substance stays steady when it is changing state?

Answer 16

The energy is no longer used to increase the temperature but instead used to break bonds between the molecules. Increasing the potential energy

Question 17

How do you calculate WD in a PV graph

Answer 17

WD = p (change in volume)

Area under the graph

Question 18

Can you state which materials heat up and cool down the fastest?

Answer 18

AIr