A transformer consists of an iron core on which are bound a primary
coil of Np turns and a secondary coil of Ns turns If the primary coil is
connected to an ac source, the primary and secondary voltages are
related by
V
NN
V
s
s
p
p
=




and the currents are related by
I
N
N
I
s
p
s
p
= 



If the secondary coil has a greater number of turns than the primary, the
voltage is stepped-up (Vs > Vp) This type of arrangement is called a step-
up transformer If the secondary coil has turns less than the primary, we
have a step-down transformer