Efficiency

Question 1

Improving efficiency

Answer 1

• lubricate moving parts to reduce friction
• use wires with as little electrical resistance as possible
• streamline the shapes of moving objects to reduce air resistance
• cut out noise (tighten loose parts to reduce vibration)

Question 2

Efficiency of a device

Answer 2

Efficiency = useful energy transferred/total energy supplied (x100)

Question 3

Why do machines waste energy?

Answer 3

• friction between moving parts, air resistance, electrical resistance, noise

Question 4

How to reduce the rate of energy transfer in house

Answer 4

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

Question 5

What is cavity wall insulation?

Answer 5

• insulation material that is used to fill the cavity between the two brick layers of an external house wall