Reducing Unwanted Energy Transfers

Question 1

Should thermal insulation have a high or low thermal conductivity?

Answer 1

Low thermal conductivity

Question 2

Describe how the cooling rate of a building relates to the thickness of its walls

Answer 2

The thicker the walls of a building, the slower the building will cool.

Question 3

Explain how thermally insulating a hot water flask reduces unwanted energy transfer

Answer 3

The low thermal conductivity of insulating materials reduces the rate of energy transfer away from the hot water flask by heating

Question 4

A lubricant is added to the hinges of a door. Suggest an unwanted energy transfer that the lubricant reduces as the door opens and closes

Answer 4

E.g. an energy transfer from the kinetic energy store of the door to the thermal energy store (of the hinge)

Question 5

Explain why decreasing the amount of energy that is wasted by a device increases its efficiency

Answer 5

Decreasing the amount of wasted energy means that a higher proportion of the supplied energy is transferred to useful stores. Efficiency = useful energy transferred by the device / the total energy supplied to the device, so the efficiency of the device is increased