Transformer
Electricity and Magnetism
Level
3
A transformer is set up to vary the voltage. The primary coil have 200 turns and the secondary coil have 500 turns, it is connected to a dc source of 100V. What is the output voltage?
The answer is 0.
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For a transformer to work, the current in one coil has to somehow make current flow in the other coil and the circuit it's connected to. A DC current in one coil will make a magnetic field on the other coil, but a magnetic field by itself won't drive any electrons around. A changing magnetic field, however does create an electric force which will accelerate those electrons in the other coil into carrying a current. You get a changing field from an AC current, since the current which makes the field is changing. The field of AC is changing mainly due to its fluctuation but DC is not fluctuating since it is constant. So, DC cannot be used to step up or down the voltage.