State what is meant by the magnetic flux linkage of a coil.
A coil of wire has 160 turns and diameter 
. The coil is situated in a uniform magnetic field of flux density 
, as shown in the figure below.
The direction of the magnetic field is along the axis of the coil. The magnetic flux density is reduced to zero in a time of 
. Show that the average e.m.f. induced in the coil is 
.
