Heat transfer

Question 1

How can heat be transferred?

Answer 1

Conduction, convection and radiation

Question 2

All objects…emit infrared radiation from their surfaces

Answer 2

continuously

Question 3

If something is hotter it releases…

Answer 3

more infrared radiation than it absorbs

Question 4

If something is cooler it releases…

Answer 4

less infrared radiation than it absorbs

Question 5

What state does conduction occur in?

Answer 5

Solids

Question 6

What state does convection occur in?

Answer 6

Liquids and gases (fluids)

Question 7

What states does radiation occur in?

Answer 7

Solids, liquids and gases

Question 8

What colour is best at emitting and absorbing infrared radiation?

Answer 8

Matt black

Question 9

What colour is best at reflecting infrared radiation?

Answer 9

Shiny white/silver

Question 10

What is the kinetic theory for solids?

Answer 10

Strong forces of attraction, closer together in a fixed and regular structure, low kinetic energy

Question 11

What is the kinetic theory for liquids?

Answer 11

Weaker forces of attraction, close together but can move past each other to form irregular arrangements, more kinetic energy

Question 12

What is the kinetic theory for gases?

Answer 12

Weak forces of attraction, very spread out, high kinetic energy so are free to move

Question 13

What happens when you heat a substance in terms of kinetic energy?

Answer 13

You give it more kinetic energy

Question 14

What is conduction?

Answer 14

Heat makes the particles vibrate more as they have more kinetic energy, colliding into neighbouring particles, causing them to vibrate more as well, causing a rise in temperature

Question 15

What makes something an insulator?

Answer 15

The particles are rather spread out so when they vibrate more they give less of an impact to neighbouring particles so don’t transfer heat as well

Question 16

Why are metals such good conductors?

Answer 16

Because they have free electrons which are free to move throughout the solid, causing more vibrations, so the heat travels faster

Question 17

What is convection?

Answer 17

When a fluid is heated the particles have more kinetic energy so move faster so they spread out and become less dense so rise above cooler, denser fluid, which sinks to the bottom and in turn is heated so gains kinetic energy, creating a convection current

Question 18

What shape containers create convection currents best?

Answer 18

Roundish or squarish containers

Question 19

What is condensation?

Answer 19

When gas cools, the particles slow down and lose kinetic energy and they move closer as the become more attracted to each other and once they are close enough together the gas becomes a liquid. This happens especially when a gas comes into contact with a cool surface

Question 20

What is evaporation?

Answer 20

When a liquid gains kinetic energy the particles at the surface if they have enough kinetic energy and are moving in the right direction they will leave the liquid and reduce the average kinetic energy of the liquid so it cools

Question 21

What can affect the rate of heat transfer?

Answer 21

The surface area, air moving over the surface, the material, the colour and what material the thing is on

Question 22

How is a flask designed to reduce heat transfer?

Answer 22

1. Double wall with a vacuum in between to stop all conduction and convection as there are no particles
2. The walls are silver to stop radiation
3. The bottle is supported by insulating foam to reduce conduction
4. The stopper is made from plastic and foam to reduce conduction

Question 23

How do animals reduce heat loss?

Answer 23

By hairs on the skin standing on end to make a thick layer of insulating air and small ears reducing the surface area

Question 24

How do animals increase heat loss?

Answer 24

By diverting blood to flow near the surface to lose heat by radiation and large ears increasing the surface area

Question 25

What is a U-value?

Answer 25

A measurement of how fast heat travels through a material

Question 26

Do you want a high or low U-value for insulating?

Answer 26

Low, because that means less heat is lost

Question 27

What insulation can a house have?

Answer 27

Cavity wall- foam stops convection, air gaps stop conduction Loft insulation- fibreglass stops convection, air gaps stop conduction Draught proofing- foam reduces convection Hot water tank jacket- stops conduction and radiation Thick curtains- reduce conduction and radiation

Question 28

What is specific heat capacity?

Answer 28

The amount of energy needed to raise the temperature of 1 kg of a substance by 1 degree

Question 29

What are the units in the specific heat capacity equation?

Answer 29

kg, degrees celcuis, Joules, J/kg degrees celcuis