# Answer to Question #7679 in Electromagnetism for muzzamil khan

Question #7679
what are the important questions in electromagnetism and is transformer a important part.
1
2012-03-27T09:29:52-0400

Some important questions in electromagnetism:

electric charges;
electric potential;
electric fields and magnetic fields;
electric current;
electromagnetic induction;
electrical generators, induction motors, transformers;
Maxwell equation;
photoelectric effect;
etc.

Transformer Equation. This quation is important!
The transformer equation relates the number of turns of wire
to the difference in voltage between the primary and secondary coils.

Vp/Vs = Np/Ns,

where Vp is the voltage in the primary coil.
Vs is the voltage in the secondary coil.
Np is the number of turns of wire on the primary coil.
Ns is the number of turns of wire on the secondary coil.

There are two points to remember.

1. Transformers only work with alternating current.
Using direct current will create a magnetic field in the core
but it will not be a changing magnetic field
and so no voltage will be induced in the secondary coil.

2. Using a step up transformer to increase the voltage
does not give you something for nothing.
As the voltage goes up, the current goes down by the same proportion.
The power equation shows that the overall power remains the same,

P = V x I & Power = Voltage x Current.

In reality, the power output is always less than the power input
because the changing magnetic field in the core
creates currents (called eddy currents) which heat the core.
This heat is then lost to the environment, it is wasted energy.

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