A step-up transformer in a school laboratory has 200 turns in its primary and 3000 turns in its…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A step-up transformer in a school laboratory has turns in its primary and turns in its secondary. The primary is joined to a V rms supply. The secondary is joined to a resistor of . Treat the transformer as ideal. Find the voltage of the secondary, the current in the resistor, the power that the resistor takes and the current in the primary.
Need a reminder? The key ideaShow
For an ideal transformer, and the power in equals the power out, , so . For a real one, the efficiency is , and is plus the losses.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The secondary voltage. V.
Step 2. The secondary current. A.
Step 3. The power. W.
Step 4. The primary current. We want , so A.
Answer: V, A, W and A.
Check. A.
Watch out. Even a small step-up transformer can give a dangerous voltage. The current in the primary is fifteen times the current in the secondary. The primary side is the one that needs the thick wire.
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