Reducing Unwanted Energy Transfers

Question 1

Describe two ways you can reduce unwanted energy transfers.

Answer 1

• Lubrication reduces energy transferred by friction
• Thermal insulation reduces the rate of energy transfer by heating

Question 2

(Exam-style question)

A woman is cycling in a race. Before the race, she puts oil on the bike chain.

Explain why putting the oil on the bike chain increases the efficiency of the woman’s cycling.

Answer 2

The oil acts as a lubricant, which reduces the energy lost due to friction

Question 3

What is conduction?

Answer 3

The process which transfers energy through an object

Question 4

State what is meant by thermal conductivity.

Answer 4

How well a material transfers energy by conduction

Question 5

Metals have a high thermal conductivity and gases, such as air, have a low thermal conductivity.

Describe the difference between high and low thermal conductivity.

Answer 5

• The lower the thermal conductivity of a material, the slower the rate of energy transfer through it
• The higher the thermal conductivity of a material, the faster the rate of energy transfer through it

Question 6

Describe how the factors of thermal conductivity and thickness affect how quickly a building cools.

Answer 6

• A building that has walls with a low thermal conductivity will cool more slowly
• A building with thick walls will cool slowly, given that the thicker a wall is, the slower the rate of energy transfer

Question 7

(Exam-style question)

A builder is trying to minimise the rate at which a house cools.

Explain one way the builder could reduce the rate at which the house cools.

Answer 7

• They could use cavity walls, which are made up of an inner and an outer wall with an air gap in the middle
• The air gap reduces the amount of energy transferred by conduction, because air has a very low thermal conductivity