Why is it that the E.M.F. Of an AC circuit can be increased or decreased, but the E.M.F. Of a DC circuit can't be?


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Oddman answered
The voltage (EMF) of "alternating current" power can be increased or decreased fairly easily using transformers. This is because the instantaneous value of the current is constantly changing, so the magnetic field around conductors of that current is constantly changing. That varying magnetic field can be made to induce current in another circuit at whatever voltage may be desired (within limits of the laws of physics and the properties of materials).

"Direct current" voltage remains constant, so cannot be stepped up or down in exactly the same way. The methods usually used involve changing it to AC and using a transformer, or making use of the property that a magnetic field does not like to change instantly. The circuits necessary to step DC voltage up or down make use of switching devices that are not as efficient in their operation as the AC transformer is.

Both AC and DC can have their EMF value changed, but the efficiency associated with doing so is much better with AC than with DC.

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