Heat Transfer

Question 1

What are the three ways heat can be transferred?

Answer 1

1. Radiation
2. Conduction
3. Convection

Question 2

What kind of EM wave transfers the most heat energy?

Answer 2

Infrared radiation.

Question 3

Where is infrared radiation emitted from?

Answer 3

Object surfaces.

Question 4

What kind of surfaces absorb and emit more radiation?

Answer 4

Dark, matt surfaces.

Question 5

How do light, shiny surfaces affect IR radiation?

Answer 5

They reflect it.

Question 6

What colour are solar panels painted and why?

Answer 6

Matt black to absorb more radiation.

Question 7

How do particles behave in a solid?

Answer 7

They vibrate about a fixed position.

Question 8

Why do the particles not move much in a solid?

Answer 8

They don’t have much energy.

Question 9

How do particles behave in a liquid?

Answer 9

They move in random directions at low speeds.

Question 10

How do the particles behave in a gas?

Answer 10

They are free to move and travel in random directions at high speeds.

Question 11

How does heating a substance affect its kinetic energy?

Answer 11

The particles gain kinetic energy.

Question 12

What is conduction?

Answer 12

Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.

Question 13

Why is conduction usually faster in denser solids?

Answer 13

The particles are closer together, so they collide more often and pass energy between them.

Question 14

Why do insulators conduct heat energy more slowly?

Answer 14

They have larger spaces between their particles.

Question 15

Why are metals good conductors of heat?

Answer 15

They have free electrons.

Question 16

Why do free electrons transfer energy more quickly than atoms?

Answer 16

They move more freely.

Question 17

What is convection?

Answer 17

Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.

Question 18

How is a convection current created?

Answer 18

1. Air particles spread out
2. Air becomes less dense
3. So the warm air rises

Question 19

What happens to the particles in a gas when it cools?

Answer 19

They slow down and lose kinetic energy.

Question 20

What is evaporation?

Answer 20

When particles escape from a liquid.

Question 21

What are the two conditions for evaporation?

Answer 21

1. Right direction

2. Enough energy

Question 22

Why does evaporation cool the liquid?

Answer 22

The particles with the most kinetic energy are most likely to escape the liquid, so the average kinetic energy of remaining particles decreases.

Question 23

Where can the cooling effect of evaporation be useful?

Answer 23

Sweating.

Question 24

What increases the rate of evaporation?

Answer 24

1. Higher temperature
2. Lower density
3. Larger surface area
4. Greater airflow over the liquid

Question 25

What increases the rate of condensation?

Answer 25

1. Lower temperature (of gas)
2. Lesser airflow
3. Lower temperature (of surface)
4. Higher density

Question 26

What does the rate of heat energy transfer depend on?

Answer 26

1. Surface area

2. Type of material

Question 27

Explain the features of a vacuum flask.

Answer 27

1. Silvered surfaces reduce IR radiation loss
2. Vacuum in the sides stops all conduction and convection
3. Insulating foam reduces conduction
4. Plastic stopper reduces conduction

Question 28

How do the hairs on your skin keep you warm?

Answer 28

Trap a thick layer of insulating air to limit heat loss by convection.

Question 29

Why do animals in warm climates have larger ears than those in cold climates?

Answer 29

To help control heat transfer.