TRANSFORMERS AND NATIONAL GRIDS
4 marks · NormalA transformer used in the National Grid has 200 turns on its primary coil and 4000 turns on its secondary coil. The input voltage is 5 V a.c.
Calculate the voltage across the secondary coil.
State whether this transformer is a step-up or step-down transformer. Give a reason for your answer.
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.
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(a) 100 V
(b) Step-up transformer, because the secondary voltage is greater than the primary voltage.
Common mistakes: Incorrect turns ratio calculation; Incorrectly identifying transformer type
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Uses transformer rule:
M2 (a) · 1 mark · Correct substitution:
A1 (a) · 1 mark · Correct calculation of output voltage (100 V).
B1 (b) · 1 mark · Correctly identifies the transformer as step-up, with reason.
Worked solution
(a) Use the transformer equation:
(b) This is a step-up transformer because the output (secondary) voltage (100 V) is greater than the input (primary) voltage (5 V).