A conducting loop of resistance R and radius r has its center at the origin of the co-ordinate system in a magnetic field of induction B axis. When it is rotated about Y-axis through 90° ,net charge flown in the coil is directly proportional to
R
r
Induced emf in the loop when the variation of flux during time dt is given as
...[2]
Using (1) and (2)
where = change in flux given as
because initially no flux is linked with the coil and it has maximum flux linkage
when turned through 90°.