GCSE Physics

Transformer Example

Here's a classic question on the workings of a transformer:
Jessie builds a transformer, connected to a 12 V a.c. power supply. She has 200 turns on the primary and 40 turns on the secondary. What is the output voltage?

From the information, we can say Vp = 12 V, Np = 200 and Ns = 40. Putting in the numbers:

Vs/12 = 40/200

This can easily be solved to give Vs = 2.4 V. But since Ns is exactly 5 times smaller than Np, it shouldn't be a surprise that Vs is also 5 times smaller than Vp!

Question: how many turns would she need on the secondary if she wanted a 24 V output?

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