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 change 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 2 equations to calculate efficiency

Answer 5

Efficiency = useful output energy transfer / total input energy transfer
Efficiency = useful power output / total power input

Question 6

How can the efficiency of a system by increased?

Answer 6

• Reducing waste output (by lubrication, thermal insulation).
• Recycling waste output (such as 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 transfer through them.

Question 9

What key factors affect the rate of cooling of a building?

Answer 9

• The thickness of the walls.

- The thermal conductivity of the walls.

Question 10

State 3 methods of reducing heat loss in a building

Answer 10

• Double glazing.
• Loft and wall insulation.
• 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.