The Open Door Web Site
Electricity and Magnetism

The Ideal Transformer
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If a transformer is described as ideal, we mean

i) the coils have zero resistance
ii) all the magnetic flux, f, produced by the primary current, Ip, is linked with the secondary coil.

When Ip changes, f changes.

From Faraday’s (Neumann’s) law, we have

Combining these two statements gives

With an ideal transformer, when the secondary coil is open circuit (not connected to anything), there is no net energy taken from the supply. Energy is stored in the magnetic field during the time the current is increasing but is recovered when the field "collapses".

 

© David Hoult 2008