Thermal Physics

Question 1

What equation links energy and specific heat capacity?

Answer 1

energy = mass x specific heat capacity x change in time

E = mcΔT

Question 2

What is

specific heat capacity?

Answer 2

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

Question 3

What is energy measured in?

Answer 3

Joules (J)

Question 4

What is mass measured in?

Answer 4

kilograms (kg)

Question 5

What is specific heat capacity measured in?

Answer 5

joules per kilogram (J/kg)

Question 6

What is temperature change measured in?

Answer 6

degrees Celsius (°C)

Question 7

What is

latent heat?

Answer 7

the energy used to make/break bonds

Question 8

How is latent heat calculated?

Answer 8

energy (required to change state) = mass x specific latent heat

E = mL

Question 9

What is specific latent heat measured in?

Answer 9

joules per kilogram (J/kg)

Question 10

Why does temperature plateau when a substance is heated?

Answer 10

because the heat energy is being used for weakening the bonds instead of increasing the temperature of the substance

and vice versa - as the bonds are strengthened they release energy

Question 11

What are the two types of

specific latent heat?

Answer 11

latent heat of fusion (solid <> liquid)
latent heat of vaporisation (liquid<> gas)

Question 12

Explain the

Evaporation Theory

Answer 12

• particles in a liquid are always moving
• they are moving at different speeds
• if a fast particle is close to the surface it might have enough energy to escape from the liquid
• (this is evaporation)
• because only the high energy particles have now escaped, the average energy of the particles which remain has decreased
• so the temperature of the liquid decreases

Question 13

What can increase the rate of evaporation?

Answer 13

• increasing airflow
• increasing temperature
• increasing surface area
• decreasing humidity

Question 14

What is the difference between evaporation and boiling?

Answer 14

• evaporation only happens at the surface of the liquid
• boiling happens throughout the liquid
• evaporation happens at any temperature
• bioling only happens at the boiling point

Question 15

State the main conduction points

Answer 15

• it is energy not particles which move from high temperature to low temperature
• when particles have more energy they vibrate faster and bump into lower energy particles - transferring the energy
• solids are better conductors than liquids and gases because the molecules are closer together so there is a higher collision rate

Question 16

State the main points about thermal conductors and thermal insulators.

Answer 16

• if a material is a good conductor of heat, the energy of the particles can be passed on easily
• in most good conductors, there are free electrons within the structure and these, as well as atoms, pass on the energy
• in insulators, there are no free electrons, so vibrations are passed on less easily

Question 17

State the main points about convection

Answer 17

• convection is the transfer of thermal energy in a substance by the movement of the particles
• convection can happen in liquids and in gases but not in solids because the particles cannot move around
• hot air and hot liquid will rise because the particles gain energy so the fluid is less dense so the denser fluids sink and the less dense fluid rises

Question 18

What are some examples of

convection?

Answer 18

• hot air balloons
• kettles
• radiators
• onshore winds

Question 19

Explain how a wall reduces the unwanted energy transfers

Answer 19

• insulation is a poor conductor because it traps air
• air is a poor conductor
• insulation reduces convection by decreasing airflow/trapping air

Question 20

Describe

absorbing radiation

Answer 20

• when energy from a high temperature object reaches a lower temperature object, some is absorbed
• dull black surfaces are better absorbers
• bright shiny surfaces are worse absorbers

Question 21

Describe

emitting radiation

Answer 21

• the amount of energy emitted by and object depends on its colour, texture and temperature
• dull black surfaces are better emitters
• bright shiny surfaces are worse emitters

Question 22

What is the law of

conservation of mass?

Answer 22

mass cannot be created or destroyed

Question 23

What is a

perfect black body?

(physics)

Answer 23

An object that absorbs all of the radiation incident on it. A black body does not reflect or transmit any radiation.

Question 24

What does the temperature of the Earth depend on?

Answer 24

• the rates of absorption
• the rates of emission of radiation or reflection