P2 - Energy Transfer by Heating

Question 1

Non-metals are better conductors than metals, true or false?

Answer 1

FALSE - metals conduct energy better than non-metals

Question 2

Which is a better conductor - copper or steel?

Answer 2

Copper

Question 3

Which is a better conductor - wood or glass?

Answer 3

Glass

Question 4

What does energy transfer by conduction depend on?

Answer 4

The materials thermal conductivity

Question 5

What is the relationship between thermal conductivity and energy transfer?

Answer 5

The greater the thermal conductivity, the more energy per second it transfers by conduction.

Question 6

What is an essential property of a good insulator?

Answer 6

They have low thermal conductivity so energy transfer through them is low.

Question 7

What three things does energy transfer through an insulator depend on?

Answer 7

1. The temperature difference across the material
2. The thickness of the material
3. The thermal conductivity of the material

Question 8

What two actions should be taken to reduce the energy transfer as much as possible?

Answer 8

1. The thermal conductivity of the insulating material should be as low as possible.
2. The thickness of the insulating layer should be as thick as possible.

Question 9

What material is the best conductor?

Answer 9

Metals

Question 10

What materials are the best insulators?

Answer 10

Non-metals such as wool and fibreglass

Question 11

When a substance is heated, what three things does its temperature rise depend on?

Answer 11

1. the amount of energy being supplied to it
2. the mass of the substance
3. what the substance is

Question 12

Define specific heat capacity?

Answer 12

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

Question 13

What is the unit of specific heat capacity?

Answer 13

Joule per kilogram degree celsius (J/kg °C).

Question 14

What is the equation for energy transferred?

Answer 14

Energy Transferred = mass x SHC x temperature change

Question 15

What is the equation for SHC?

Answer 15

SHC = Energy transferred / mass x temperature change

Question 16

True or False - the greater the mass of an object, the faster its temperature increases when heated?

Answer 16

FALSE - the greater the mass of an object, the slower its temperature increases when heated.

Question 17

What is the role of storage heaters and how do they work?

Answer 17

They use electricity at night to heat bricks or concrete blocks which are inside the heater. Energy transfer from the bricks helps to keep the room warm. As the bricks have a high SHC, they store lots of energy. They warm up slowly and cool down slowly when the heater is turned off.

Question 18

What different types of heating can you get in a home?

Answer 18

Electric heaters
Gas heaters 
Oil central heating 
Gas central heating 
Solid fuel in stoves or fireplaces

Question 19

Give 5 ways energy transfer from the home to the outside can be reduced?

Answer 19

1. Loft insulation
2. Cavity wall insulation
3. Thicker bricks with lower thermal conductivity
4. Double-glazed windows
5. Aluminium foil between the radiator and the wall

Question 20

What is a good material to use for loft insulation?

Answer 20

Fibreglass

Question 21

How does fibreglass reduce energy transfer to the outside and save money?

Answer 21

It is a good insulator and the air between the fibres reduces the rate of energy transfer by conduction. The more layers of insulation, the thicker it will be and the rate of energy transfer through the roof will be less.

Question 22

How does cavity wall insulation reduce energy transfer to the outside and save money?

Answer 22

It reduces the rate of energy transfer through the outer walls of the house. The cavity (space between the two layers of bricks that make up the wall) is filled with air. When cavity wall insulation is put in, it is a better insulator than the air and traps the air in small pockets, reducing the rate of energy transfer by conduction.

Question 23

How does aluminium foil between the radiator and the wall reduce energy transfer to the outside and save money?

Answer 23

It reflects radiation away from the wall and so reduces the rate of energy transfer by radiation.

Question 24

How do double-glazed windows reduce energy transfer to the outside and save money?

Answer 24

They have two glass panes with dry air or a vacuum between them. The thicker the glass and the lower its thermal conductivity, the slower the rate of transfer of energy by conduction. Dry air is an insulator hence reduces the rate of energy transfer by conduction. A vacuum prevents energy transfer by convection.

Question 25

How do thicker bricks reduce energy transfer to the outside and save money?

Answer 25

Thicker bricks with lower thermal conductivity mean the rate of transfer of energy from the inside to outside will be lower.

Question 26

How do solar panels work?

Answer 26

They absorb infrared radiation from the Sun and are used to generate electricity or heat water.

Question 27

What is the difference between the roles of solar cell panels and solar heating panels?

Answer 27

Solar cell panels generate electricity directly and solar heating panels heat water directly.

Question 28

Which direction is a solar panel fitted in the northern hemisphere?

Answer 28

It is fitted on a roof that faces south so it can absorb as much infrared radiation from the Sun as possible