TRANSFORMERS AND NATIONAL GRIDS
4 marks · NormalA step-up transformer in the National Grid has 120 turns on its primary coil and 6,000 turns on its secondary coil. The primary coil is connected to an alternating voltage of 8 V.
Calculate the voltage across the secondary coil.
Explain whether this transformer increases or decreases the current in the secondary coil compared to the primary coil, assuming 100% efficiency.
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) 400 V
(b) The transformer decreases the current in the secondary coil.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitutes correct numbers into transformer equation (V_p / V_s = N_p / N_s).
M2 (a) · 1 mark · Rearranges to find V_s.
A1 (a) · 1 mark · Correct answer (400 V) with appropriate unit.
B1 (b) · 1 mark · Explanation referencing current is decreased.
Worked solution
(b) For a step-up transformer, the voltage increases so (for equal power) the current decreases.