6.6 Transformers

A transformer is an essential part of power transportation, and plays an important role in getting the right electricity into your home. A transformer also works along the principle of electromagnetic induction. This is the general structure of a transformer:

1. A U-shaped soft iron core, which is easily magnetized, sometimes with a further bar of iron across the top of the U.

2. Two separate solenoids coiled around opposite sides of the U

When an A.C. current is passed through one of the solenoids, a magnetic field is produced, but since the current is A.C., this magnetic field is constantly changing. As stated by Faraday’s Law, a changing magnetic field induces an E.M.F. in a conductor, this case the second solenoid. The current in this solenoid is once again A.C. Because energy is always conserved (in a 100% efficient transformer), the input power of a transformer is always equal to the power output. It is the coils of the two solenoids that allow both the current and the voltage of the input power to be transformed, according to this equation:

or

where N_P is the number of coils on the primary solenoid, N_S is the number on the secondary solenoid, and V_P and V_S are their respective voltages.

And, since P_P = P_S, (due to the law of conservation of energy)

Of course, this is only true of a 100% efficient transformer, which is assumed in many cases.