An ideal transformer steps 230 V mains down to 11.5 V for a doorbell. Its secondary coil has 200 turns. Calculate the number of turns on the primary coil.

Electromagnetism Challenge #4 — Transformers

The turns ratio of
a transformer.

Electromagnetism Hard

Problem

An ideal transformer steps the 230 V mains down to 11.5 V for a doorbell. The secondary coil has 200 turns. Calculate the number of turns on the primary coil.

Primary voltage\( V_p = 230\ \mathrm{V} \)
Secondary voltage\( V_s = 11.5\ \mathrm{V} \)
Secondary turns\( N_s = 200 \)
Answer asnumber of turns

Ideal transformer — no energy is lost in the core.

Hint: the voltages sit in the same ratio as the turns: \( \tfrac{V_p}{V_s} = \tfrac{N_p}{N_s} \). A step-DOWN transformer needs more turns on which side?

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The turns ratio ofa transformer.

Problem

Submit your answer

The turns ratio of
a transformer.