In  transformer, there are two coils, primary coil and secondary coil.

Let, I₁ and I₂ are the currents in primary coil and secondary coil.

N₁ and N₂ are the number of turns in primary coil and secondary coil respectively,

ε₁ and ε₂ are the input and output emf.

So, the relation of these is as below-

I₁/I₂ = ε₂/ε₁ = N₂/N₁