Chapter 1.7 Energy and efficiency

Question 1

What is the equation of the efficiency of a device?

Answer 1

The efficiency of a device = useful energy transferred by the device ÷ total energy supplied to the device (x100%).

Question 2

Why do machines waste energy?

Answer 2

Machines waste energy because of friction between their moving parts, air resistance, electrical resistance, and noise.

Question 3

How can machines be made more efficient?

Answer 3

Machines can be made more efficient by reducing the energy they waste. For example, lubrication is used to reduce friction between moving parts.

Question 4

Because energy cannot be created or destroyed:

Answer 4

Input energy (energy supplied,J) = useful output energy (useful transferred,J) + energy wasted (J)

Question 5

What is weight measured in?

Answer 5

Weight is measured in newtons (N). The weight of 1 kilogram object on the Earth’s surface is about 10N

Question 6

What is energy measured in?

Answer 6

Energy is measured in joules (J). The energy needed to lift a weight of 1 newton by a height of 1 metre is equal to 1 joule.