THE TRANSFORMER
3 marks · EasyA transformer is used to reduce the voltage from a mains a.c. supply of 120 V to 12 V for use in a toy train set. The primary coil has 480 turns.
Is this a step-up or a step-down transformer? Explain your answer.
Calculate the number of turns that should be on the secondary 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
(a) Step-down transformer, because output voltage is less than input.
(b) 48 turns
Common mistakes: Dividing turns instead of using transformer equation
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies as 'step-down transformer' and states output voltage is lower than input.
M1 (b) · 1 mark · Uses the correct transformer equation with correct values substituted.
A1 (b) · 1 mark · Finds correct number of secondary turns: 48.
Worked solution
a) Step-down transformer, as the secondary (output) voltage is less than the primary (input) voltage.