Energy Transfer By Heating

Question 1

What is heat radiation?

Answer 1

The transfer of heat using infrared.

Question 2

What factors affect the rate at which objects emit and absorb heat?

Answer 2

Tenperature and the colour/texture of the surface.

Question 3

How does temperature affect the rate at which an object emits and absorbs heat?

Answer 3

An object that is hotter than its surroundings emits more radiation.

An object that’s colder than its surroundings absorbs more energy from its surroundings.

Question 4

How does surface colour/texture affect the rate at which an object emits and absorbs heat?

Answer 4

Dark, matt surfaces emit and absorb a lot more radiation than white, glossy surfaces.

Question 5

How the particles in a solid arranged?

Answer 5

They have a fixed, regular arrangement due to strong forces of attraction. The particles have little-to-no energy so only vibrate on a fixed spot.

Question 6

How the particles in a liquid arranged?

Answer 6

They can move freely past each other and form irregular arrangements as they have weaker forces of attraction. The particles have some energy so can move randomly but slowly.

Question 7

How the particles in a gas arranged?

Answer 7

They move randomly and at high speeds because they have lots of energy. There are hardly any forces of attraction between the particles.

Question 8

What happens when you heat an object?

Answer 8

The particles gain energy so begin to vibrate more violently.

Question 9

How does conduction work?

Answer 9

When particles are heated they collide with each other and pass energy on. The process continues until the energy has completely passed through the solid. At this stage the object begins to feel warmer.

Question 10

What makes a good conductor?

Answer 10

A dense solid as the particles are closer together.

Question 11

What makes metals good conductors?

Answer 11

They gave a delocalised electron.

Question 12

What is convection?

Answer 12

When more energetic particles in a liquid or gas move from a hotter region to a cooler region.

Question 13

How do immersion heaters work?

Answer 13

1) A heater coil is placed in a water tank.
2) Water particles near the heater cool gain energy and so heat up.
3) Hot water is less dense than cold water so the warm water rises to the top.
4) The cold water sinks to the bottom of the tank because it is displaced by the hot water. The cold water is then heated and the cycle begins again.

Question 14

How do radiators make a whole room warm?

Answer 14

Hot, less dense air by the radiator rises and cooler air moves next to the radiator to be warmed.

Question 15

What is condensation?

Answer 15

When a gas cools, the particles slow down and lose energy. The attractive forces pull them closer together and form a liquid again.

Question 16

What is evaporation?

Answer 16

When particles escape a liquid to form a gas.

Question 17

What two things decide whether or not particles can evaporate?

Answer 17

• The direction the particle is heading in.

* Whether or not the particle has enough energy to overcome the attractive forces in the liquid.

Question 18

Why does evaporation have a cooling effect?

Answer 18

Because the particles with the most energy escape, meaning the average energy in the liquid decreases. This in turn decreases the temperature’s temperature.

Question 19

What conditions make evaporation easier?

Answer 19

• Higher temperature means particles have more energy.
• Less dense liquids have weakest forces of attraction.
• Large surface area means there’s more chance of particles escaping.
• More airflow means gas particles are replaced quicker.

Question 20

What conditions make condensation easier?

Answer 20

• Lower temperatures mean that the particles have less energy.
• Higher concentration means particles are closer together.

Question 21

What factors affect the rate of energy transfer?

Answer 21

• The difference in temperature between the object and its surroundings.
• The surface area of the object.
• The surface area to volume ratio.
• The conductivity of the object.

Question 22

How do vacuum flasks control heat transfer?

Answer 22

• Glass bottle is double-walled with a vacuum to stop conduction and convection.
• The walls either side of the vacuum are silvered to limit heat loss by radiation.
• The bottle is supported by insulating foam.
• The stopper is plastic and filled with cork or foam to reduce heat conduction.

Question 23

How do you humans and animals control energy transfer?

Answer 23

• In the cold, hairs stand up to catch an insulating layer of air.
• When we are warm, blood runs closer to the surface of our skin to increase heat loss.

Question 24

How can cavity wall insulation prevent heat loss in the home?

Answer 24

By filling gaps between walls with foam, convection currents are stopped and radiation and conduction are reduced.

Question 25

How can loft insulation prevent heat loss in the home?

Answer 25

It traps pockets of air which reduces conduction and convection.

Question 26

What is loft insulation?

Answer 26

Layers of fibreglass backed into lofts.

Question 27

How does one achieve draft proofing? What does it do?

Answer 27

It is achieved by putting strips of foam and plastic around the edges of doors and windows. This limits convection.

Question 28

What is double glazing? What does it do?

Answer 28

Double glazing using two layers of glass or plastic separated by a gap of air. This reduces conduction.

Question 29

What is. Hot water tank jacket made of? What does it do?

Answer 29

Fibreglass. It traps pockets of air to limit conduction and convection.

Question 30

How can thick curtains prevent heat loss in the home?

Answer 30

They reduce convection.

Question 31

How can we measure the effectiveness of an energy saving method?

Answer 31

The most effective methods save the most money. Eventually, the money saved will equal the original investment. This is called payback time. The shorter the payback time, the more effective the solution.

Question 32

How do you calculate payback time?

Answer 32

Annual saving

Question 33

What is a U Value?

Answer 33

A measure of how good an insulator something is. The lower the U Value, the better the insulator.

Question 34

What are Solar Hot Water Panels?

Answer 34

Solar panels with black surfaces that contain water pipes. Radiation taken in by the black surface heats the water.

Question 35

What is specific heat capacity?

Answer 35

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

Question 36

What is the formula used with specific heat capacity?

Answer 36

E= mcθ

E=Energy transferred (J)

m= Mass (kg)

c= specific heat capacity (J/kgdegrees)

θ= temperature change