Primary and Secondary Current in Transformers

Although we can make the secondary voltage greater than the primary voltage in a transformer, this does not mean energy is created. Energy is still conserved.

In an ideal transformer, there is no loss of energy. Hence,

Power supplied to the primary coil = Power used in the secondary coil

That is,

VpIp = VsIs

Vp = Primary voltage , Ip = Primary current

Vs = Secondary voltage, Is = Secondary current

(Remember, Power, P = IV)

Which brings us to the ratio of current which is

Is / Ip = Vp / Vs

This means that if the voltage is stepped-up, the current in the secondary coil is stepped-down by the same ratio.

Comparing the transformer equation.

Vs / Vp = Ns / Np

We ultimately get

Is / Ip = Np / Ns

(Ns = number of coils in secondary coil)

(Np = number of coils in primary coil)