4.1.2 Conservation and dissipation of energy

Question 1

State the law of energy conservation

Answer 1

Energy cannot be created or destroyed (it can only be transferred into different forms)

Question 2

State any changes in the total energy of a ball that is kicked, assuming that no external forces act.

Answer 2

The total energy of the system remains constant due to the conservation of energy.

Question 3

What is waste energy?

Answer 3

The energy that is not used by the device for its desired purpose.

Question 4

Describe the energy changes that occur in a filament light-bulb

Answer 4

• Electrical energy is transferred into light and heat energy.
• light is a useful energy form, heat is waste energy.

Question 5

State two equations to calculate efficiency

Answer 5

• Efficiency = useful output energy transfer / Total input energy transfer
• Efficiency = Useful power output / total power output

Question 6

How can efficiency of a system be increased?

Answer 6

1. Reducing waste output (by lubrication, thermal insulation etc.)
2. Recycling waste output (eg. Recycling thermal waste energy as input energy)

Question 7

State the consequence for energy transfer of a material with a high thermal conductivity.

Answer 7

The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity.

Question 8

Do double-glazed windows have a higher or lower thermal conductivity than single-glazed windows?

Answer 8

Lower, meaning less energy transfers through them

Question 9

What key factors affect the rate of cooling a building

Answer 9

• The thickness of the walls
• The thermal conductivity of the walls

Question 10

State three methods of reducing heat loss in a building

Answer 10

1. Double glazing
2. Loft and wall insulation
3. Thicker walls

Question 11

How can the efficiency of a mechanical machine with moving parts be improved?

Answer 11

Lubricate any moving parts to reduce the friction and therefore energy loss due to heating

Question 12

How can the efficiency of a radiator be improved?

Answer 12

Installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed into the walls.

Question 13

How can the efficiency of boiling water in a pan be improved?

Answer 13

By placing a lid on the pan to reduce the heat loss from the top.