Module 5.1 - Thermal Physics

Question 1

What is an absolute/thermodynamic scale of temperature?

Answer 1

Independent of the properties of any specific substance

Measured in kelvin (K)

Question 2

What is absolute zero?

Answer 2

The temperature at which a substance has minimum internal energy (lowest limit for temperature - 0K)

Question 3

Define thermal equilibrium

Answer 3

Objects in contact with each other at the same temperature with no net heat flow between them

Question 4

What is temperature?

Answer 4

A measure of how hot or cold an object is

Question 5

What affects the temperature of a material?

Answer 5

The internal kinetic energy (higher KE of particles means higher temperature)

Question 6

How can an object have a high temperature but not store/transfer a lot of thermal energy?

Answer 6

The particles may have a lot of energy each so there is a high temperature, but if the mass is lower/there are less particles the total energy will be lower so it has less thermal energy

Question 7

How is thermal energy transferred?

Answer 7

From regions of higher temperature to lower temperature

Question 8

Points about solids

Answer 8

Particles close together
Vibrate around individual fixed position
Held together by strong interatomic forces
High density
Definite fixed (lattice) shape

Question 9

Points about liquids

Answer 9

Particles can’t move much
Slide past each other
Mean separation of particles is greater than in solids
Weaker interatomic forces than solids
Lower density than solids
No fixed shape - can flow and be poured

Question 10

Points about gases

Answer 10

Particles free to move around quickly and in random directions
High mean separation of particles
Very weak interatomic forces
Much lower density than solids and liquids
Easily compressed

Question 11

Formula for density

Answer 11

Mass of one molecule x number of molecules per cubic metre

Question 12

Define internal energy

Answer 12

The sum of all the randomly distributed kinetic and potential energies of all the particles (atoms, molecules, ions) in the system

Question 13

What is the kinetic energy of a system due to?

Answer 13

Movement of particles within the system

Greater mass and velocity of particles means greater kinetic energy

Question 14

Where is the potential energy of a system stored?

Answer 14

In bonds and intermolecular forces between particles

Question 15

What happens to the kinetic energy component of the internal energy during a change of state?

Answer 15

No change as there is no change in temperature

Question 16

What happens to the potential energy component of the internal energy during a change of state?

Answer 16

Will change as intermolecular forces are overcome

Question 17

Define specific heat capacity

Answer 17

The amount of energy required to raise the temperature of 1kg of a substance by 1°C

Question 18

Define specific latent heat

Answer 18

The amount of energy required to change the state of 1kg of a substance

Question 19

Observations and conclusions of Brownian Motion

Answer 19

Can see smoke particles but not air - air molecules must be very small
Lots of changes in direction - lots of air molecules (collisions)
Rapid changes in direction - must have high momentum, small mass so probably large velocity
No pattern in motion - random motion

Question 20

Features of an ideal gas

Answer 20

Contains a large number of particles
Particles move rapidly and randomly
All collisions are perfectly elastic
Attractive forces between particles during collisions are negligible
Time for collision to happen is negligible compared to time in between collisions
Compared to the volume of gas in the container, the particle volume is negligible

Question 21

How is gas pressure created?

Answer 21

By collisions of gas particles with the walls of the container

Question 22

Which feature of an ideal gas is least likely to be true?

Answer 22

Attractive forces between particles during collisions are negligible

Question 23

Why is it called the Kinetic Theory?

Answer 23

There is no potential energy, as all internal energy is kinetic

Question 24

Why is the usual pressure equation (P = F/A) not useful for gases?

Answer 24

Gases are in a volume, not across an area

Question 25

What is Boyle’s Law?

Answer 25

The volume of a fixed volume of gas is inversely proportional to the pressure exerted on the gas, under conditions of constant temperature
pV = constant under conditions of constant temperature
p1V1 = p2V2

Question 26

Why should you wait in between readings in the Boyle’s Law experiment?

Answer 26

Internal energy of a gas changes as it gains heat energy or if work is done on it
If a gas is going to stay at the same temperature, its internal energy must not change
This means the gas must lose heat when work is done on it during compression if it is to stay at a constant temperature

Question 27

What is the the Pressure Law?

Answer 27

Pressure is directly proportional to temperature for a constant volume
P/T = constant
P1/T1 = P2/T2

Question 28

Problems with the pressure law apparatus

Answer 28

Actually measuring pressure in connecting tubes, not the flask
Need a perfect seal at either end of the tube
Air cools as it leaves the flask

Question 29

Application of the pressure law

Answer 29

Because P changes linearly with T, the apparatus can be used as a thermometer
Called a constant volume gas thermometer and is used to define our temperature scales
Too big and slow for everyday use, so is used to calibrate other types of thermometers