If the length RQ = x and RS = l, the
magnetic flux FB enclosed  by the loop PQRS
will be
FB = Blx
Since x is changing with time, the rate of change
of flux FB will induce an emf given by:
(
)
– d
–d
d
d
B
Blx
t
t
Φ
ε =
=
   = 
d
–
d
x
Bl
t =Blv
(6 5)
FIGURE 6 10  The arm PQ is moved to the left
side, thus decreasing the area of the
rectangular loop This movement
induces a current I as shown