GCSE PHYSICS - The Transformer Equation - Voltage - Number of Turns of Wire - Power

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The Transformer Equation.

This equation is important!

The transformer equation relates the
number of turns of wire to the difference in voltage
between the primary and secondary coils.

^V^p/_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 output power is always less than the input power
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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