The value of this emf depends on the number of
turns in the secondary We consider an ideal transformer in which the
primary has negligible resistance and all the flux in the core links both
primary and secondary windings Let f be the flux in each turn in the core
at time t due to current in the primary when a voltage vp is applied to it Then the induced emf or voltage es, in the secondary with Ns turns is
d
d
s
Ns
φt
ε
= −
(7