ENERGY IN TRANSFORMERS

3 marks · Normal

(a)

State the meaning of 100% efficiency in a transformer.

[1 mark]

(b)

A transformer has an efficiency of 100%. The secondary coil provides an output power of 60 W. What is the input power?

[2 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) All input energy is converted to output energy with no loss. · must show No energy lost / all input power transferred / input power = output power

(b) 60 W · must show States input power equals output power

Common mistakes: Confusing input and output when 100% efficient

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · States 100% efficiency means all input energy/power appears in output, no losses/energy wasted.

B2 (b) · 1 mark · Recognizes input power equals output power for 100% efficiency.

A1 (b) · 1 mark · Gives correct value: 60 W (with or without unit).

Worked solution

a) A transformer with 100% efficiency transfers all input power to output with no losses.

b) If the output power is 60 W and efficiency is 100%, the input power must also be 60 W.