Thermal Physics

Question 1

What is the kinetic theory of matter?

Answer 1

All matter is made up of small particles which are moving.

Question 2

Define temperature

Answer 2

The average kinetic energy of the particles in that material.

Question 3

Define specific heat capacity

Answer 3

The heat energy required to change the temperature of 1kg of the material by 1K without a change in state.

Question 4

What is the specific heat capacity of water?

Answer 4

4200J/kgK

Question 5

How is the specific heat capacity of a material calculated?

Answer 5

c = Q/mΔT

Question 6

What is Newton’s law of cooling?

Answer 6

A rate of energy loss per second from an object which is proportional to the temperature difference between the object and its surroundings.

Question 7

Define latent heat of fusion.

Answer 7

The heat energy required to change 1kg of a material from a solid to a liquid without a change in temperature.

Question 8

How is the energy needed to change a mass of a material from a solid to a liquid calculated?

Answer 8

Q=mL

Question 9

Define latent heat of vapourisation.

Answer 9

The heat energy required to change 1kg of a material from a liquid to a gas with no change in temperature.

Question 10

Describe the shape of a cooling curve

Answer 10

• The rate of temperature change is initially high.
• There is no temperature change as the material changes state.
• The rate of temperature change decreases as the temperature of the material nears the temperature of the surroundings.

Question 11

Why is there no temperature change when changing state?

Answer 11

The rate of heat energy produced by bond formation is equal to the rate of heat energy lost due to cooling.

Question 12

How is the specific heat capacity of a material found from a constant heating graph?

Answer 12

c = P/(m x gradient)

Question 13

How is the latent heat of fusion of a material found from a constant heating graph?

Answer 13

L = Pt/m where t = time taken for the solid to melt

Question 14

Define the atomic mass unit.

Answer 14

1/12 of the mass of a Carbon 12 atom

Question 15

Describe and explain the nature of the radiation that may be emitted from an excited
nucleus of the moderator.

Answer 15

Gamma radiation since nucleus de-excites in discrete energy levels.

Question 16

Outline what is meant by an ideal gas

Answer 16

The gas obeys the ideal gas law at all temperatures/pressures.

Question 17

Explain what is meant by the Rayleigh criterion

Answer 17

Two sources will be resolved if the central maximum of the diffraction pattern of one coincides with the first minimum of the other.

Question 18

How is the age of the universe found from Hubble’s constant?

Answer 18

Age = 1/H

kmS^-1Mpc^-1 –> ms^-1pc^-1 –> ms^-1m^-1

Question 19

What is a binary system?

Answer 19

Two stars revolving about a common centre of mass.

Question 20

State what is meant by the binding energy of a nucleus

Answer 20

the amount of energy required to separate a nucleus into its separate neutrons and protons/nucleons

Question 21

State and explain the purpose of the concrete other than its structural function for a nuclear reactor core.

Answer 21

forms a shield to reduce the intensity of radiation

from neutron radiation

Question 22

Explain what is meant by the Big Bang theory

Answer 22

- The universe has expanded from a
single hot dense point 
- Evidence comes from the Hubble
relationship and observations of the red
shift of distant galaxies.
- This shows that the galaxies are
moving outwards from a single common
point.
-  evidence comes from
the cosmological microwave background
radiation 
- This follows a black body radiation
curve which corresponds to a temperature
of 2.7 K
- This can be interpreted as the left
over “heat” of the big bang,
Hydrogen and helium is present in
the Universe in the ratio 3:1
- This supports the idea that a very
brief period of fusion occurred when the
Universe was very young, which is
consistent with the Big Bang theory.

Question 23

State what is meant by a standard candle.

Answer 23

an object whose absolute magnitude is known

Question 24

Explain how measurements of a type 1a supernova can be used to determine how far
away it is from the Earth.

Answer 24

All type 1a supernovae have same peak absolute magnitude
Apparent magnitude can be measured (at this peak).
ref to m-M = 5 log (d/10)

Question 25

Explain what is meant by a parsec.

Answer 25

1 pc is the distance at which 1AU subtends an angle of 1 arc second.

Question 26

What is a decay constant?

Answer 26

probability of decay per unit time

Question 27

Give two reasons why it is difficult to obtain a reliable age from carbon dating

Answer 27

• May use wood from long after tree was dead.

- Different levels of carbon 14