GCSE Standard Questions: The Motor Effect

Q7. Motors change electrical energy into kinetic energy.

Look at the information about five different electric motors in the table below.

Electric motor	Energy input per hour (J)	Useful energy output per hour (J)	Energy 'wasted' per hour (J)
A	72000	60000
B	54000	36000
C	18000		3000
D		48000	12000
E	54000	48000

(a)

(i) Calculate the energy input per hour in J for electric motor D.

[2 marks]

(ii) Which electric motor has the lowest 'wasted' energy in one hour?

[1 mark]

(iii) Which electric motor has the highest 'wasted' energy in one hour?

[1 mark]

(iv) Describe how energy is 'wasted' in an electric motor.

[1 mark]

(v) Suggest how this 'wasted' energy can be reduced in an electric motor.

[1 mark]

(b) Calculate the % efficiency of electric motor E.

Give your answer to two significant figures.

[4 marks]

(Total 10 marks)