Chapter 2 Energy Transfer By Heating

Question 1

What are the best conductors?

Answer 1

Metals are the best conductors of energy. The higher the thermal conductivity of a material, the higher the rate of energy transfer through it

Question 2

What are the best insulators?

Answer 2

Non-metals such as wood and fibre-glass. The thicker a layer of insulation material the lower the rate of energy transfer through it

Question 3

What does the energy transfer through a layer of insulating material depend on?

Answer 3

-The temperature difference across the material
- the thickness of the material
- the thermal conductivity of the material
To reduce the energy transfer:
- thermal conductivity should be low
- thickness should be as thick as possible

Question 4

What is specific heat capacity?

Answer 4

The amount of energy needed to change the temp of 1kg of the substance by 1 degree

Question 5

Specific heat capacity equation

Answer 5

Energy transfered(joules)= mass(kilograms) x specific heat capacity(joules per kilogram) x temp change (degree C)

Question 6

Specific heat capacity units

Answer 6

Joules per degree C

Question 7

What does specific heat capacity depend on?

Answer 7

The greater the mass of the object the more slowly it’s temperature increases when heated

Question 9

How can the rate of energy transfer be reduced?

Answer 9

• loft insulation
• cavity wall insulation
• double glazed windows
• aluminium foil behind radiators
• external walls with thicker bricks and lower thermal conductivity

Question 10

Loft insulation

Answer 10

Such as fibreglass reduces the rate of energy transfer through roof. Good insulator. Air between river reduces rate of energy transfer by conduction

Question 11

Cavity wall insulation

Answer 11

Reduce the rate of energy transfer between the outer walls of the house. The cavity of an outer wall is the space between 2 layers of brick that makes up the wall , insulation is pumped into the cavity. Traps small air pockets, reducing the rate energy transfers by conduction

Question 12

Aluminium foil

Answer 12

Between radiator and the wall reflects radiation away from wall and reduce rate of energy transfer by radiation

Question 13

Double glazing windows

Answer 13

2 panes of glass with dry air or a vacuum between the panes. The thicker the panes the lower the thermal conductivity. Vacuum prevents energy transfer by convection

Question 14

Solar panels

Answer 14

Absorb infrared radiation from the sun and generate electricity.