We consider a source which produces
sinusoidally varying potential difference across its
terminals Let this potential difference, also called ac
voltage, be given by
msin
v
v
ωt
=
(7 1)
where vm is the amplitude of the oscillating potential
difference and w  is its angular frequency To find the value of current through the resistor, we
apply Kirchhoff’s loop rule 
∑ε( )t =
0 (refer to Section
3