Thermal Physics

Question 1

What is thermal equilibrium

Answer 1

There is no net flow of thermal energy between phases

Question 2

What is the kinetic model

Answer 2

A model that describes how all substances are made up atoms or molecules which are arranged differently depending on phase.

Question 3

How are solids arranged

Answer 3

• Regularly arranged
• Packed closely together
• Strong electrostatic forces holding them in fixed positions

Question 4

How are liquids arranged

Answer 4

• Atoms or molecules packed closely together
• Have more kinetic energy than solids
• They can change position and flow past each other

Question 5

How are gases arranged

Answer 5

• Atoms and molecules are much further apart
• Have more kinetic energy than liquid
• Negligible electrostatic forces between them unless they collide
• They move randomly in different directions and speed

Question 6

Brownian motion

Answer 6

The continuous random motion of small particles suspended in a fluid visible under a microscope

Question 7

How to observe Brownian motion

Answer 7

By observing smoke particles under a microscope, showing the random movement

Question 8

What is internal energy

Answer 8

The sum of random distributions of kinetic and potential energies within the molecules in a system

Question 9

Absolute zero

Answer 9

The lowest limit for temperature (0k), the temperature at which a substance has minimum internal energy

Question 10

What happens to temperature and internal energy as a substance changes phase

Answer 10

• Temperature remains constant
• There is no change in kinetic energy because temperature is constant during melting
• If a substance is melting potential energy increases and so internal energy increases

Question 11

As temperature of a body rises how does internal energy change

Answer 11

Internal energy increases

Question 12

Specific heat capacity

Answer 12

The energy needed to heat a 1kg of mass by 1 kelvin

Question 13

Determining specific heat capacity

Answer 13

• Place a heater a material
• Heat for a set time recording current and potential difference across the heater using an ammeter and voltmeter
• Measure temperature using a temperature probe
• Plot a temperature time graph
• Where gradient is power/mass x specific heat capacity.

Question 14

What is specific latent heat

Answer 14

Energy needed to change the phase per unit mass

Question 15

What is specific latent heat of fusion

Answer 15

When a substance changes phase from a solid to a liquid

Question 16

What is specific heat of vaporisation

Answer 16

When a substance changes from a liquid to a gas

Question 17

Determining specific latent heat of fusion

Answer 17

• Place a heater into ice for a set time
• Measure the potential difference and current across the heater
• Collect the melted mass of the ice and find it mass
• Energy/mass melted = specific latent heat of fusion
• E=IVt

Question 18

Determining specific latent heat of vaporisation

Answer 18

• Place the heater in water for a set time
• Measure the potential difference and current across the heater
• Let the evaporated water to condense and collect the water
• Measure the mass of water
• Specific latent heat of vaporisation = energy/mass evaporated

Question 19

How to calculate the mass of a molecule

Answer 19

Molar mass/ avogadros constant

Question 20

Assumptions of the model of kinetic theory of gases

Answer 20

• Large number of molecules in random, rapid motion
• Particles occupy negligible volume compared to the volume of gas
• All collisions are perfectly elastic and the time of the collision is negligible to the time between collisions
• Electrostatic forces between atoms or molecules are negligible except during collisions

Question 21

What does N stand for?

What does n stand for?

Answer 21

N=number of particles

n=number of moles

Question 22

Boyle’s law

Answer 22

Pressure is inversely proportional to volume for a fix mass at a constant temperature

Question 23

Explain in terms of the behaviour of molecules, how a gas exerts a pressure on the wall

Answer 23

• Molecules collide with the wall
• There is a change of momentum of the molecule from the wall
• There is a force exerted on the wall by the molecules and there is a force exerted on the molecules by the wall
• Pressure experience on the wall of force/ area

Question 24

Gas laws other than boyle’s

Answer 24

Pressure is directly proportional to temperature

Pressure x volume / temperature = constant

Question 25

Maxwell boltzman distribution

Answer 25

See graph in notes

Question 26

Calculating absolute zero

Answer 26

• Place a volume of dry air in a flask into a water bath
• Record pressure of air with a pressure gage and temperature of water with a temperature probe
• Plot a pressure temperature graph
• Find the equation of the line
• Substitute y=0 and the solve for x
• Should equal -273k

Question 27

Investigating boyle’s law

Answer 27

• Attach a pump to a volume scale and a pressure gage
• Record atmospheric pressure and volume
• Pump to change the volume scale
• Slowly decrease pressure changing the volume at intervals
• Plot pressure against 1/volume graph