USING TRANSFORMERS TO CHANGE VOLTAGES

4 marks · Normal

A step-down transformer is used to supply 6 V to a device. The primary coil has 240 turns and the secondary coil has 40 turns. What is the input voltage supplied to the primary coil?

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

36 V (±0.5)

Common mistakes: Incorrect use of coil ratio (inverting input/output); Arithmetic error

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Writes transformer equation .

M2 · 1 mark · Substitutes correct values.

A1 · 1 mark · Rearranges to find input voltage.

A2 · 1 mark · Evaluates correct input voltage as 36 V (accept follow-through). (follow-through)

Worked solution

Use the transformer equation:

Let .

The input voltage must be 36 V.