EasyPhysicsHigh School (11–12)Electricity & Magnetism › Alternating CurrentNumericalBoard ExamA-LevelIB
A small radio has a transformer with 1150 turns in its primary and 100 turns in its secondary…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A small radio has a transformer with turns in its primary and turns in its secondary. The primary is joined to the V mains. The radio takes A from the secondary. Treat the transformer as ideal. Find the voltage of the secondary 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.
Given. , , V and A.
Plan. We find from the ratio of the turns. We then find from the power, or from the inverse ratio.
Step 1. The secondary voltage. V.
Step 2. The power. W.
Step 3. The primary current. We want , so A.
Answer: V and A.
Check. A. It agrees.
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