Why Doesn't DC Work With a Transformer?

Yesterday a friend of mine asked me a question about direct current. His question was: If you send direct current to the primary coil of a transformer, why won't there be any power transferred to the second circuit? I've always been bad at Physics so I didn't know the answer but I'm curious. Thanks for your help.
- Mike Wanders (age 27)
New York

Hello Mike,

You need to know just a little bit of Electricity and Magnetism (EM) to understand the phenomenon.  One of the basic laws discovered by Michael Farady back in the 19th century, is called the Law of Induction.  You might take a look at for more information.   The basic reason is that you need a changing magnetic field in order to induce a voltage in a loop of wire.  So transformers work with AC since the magnetic field is oscillating at 60 Hertz.   If you plug the transformer into a DC circuit, the magnetic field is a constant, after a short initial spike.  No oscillating magnetic field, no output voltage.

 

LeeH

(published on 02/15/2014)