Q: A coil is placed in a transverse magnetic field of 0.02 T. If this coil starts shrinking at a rate of 1 mm/s, while its radius remains 4 cm, then what is the value of induced e.m.f.?
(a) 2 μV
(b) 5 μV
(c) 8 μV
(d) 50 μV
Ans: (b)
Sol: Here, B = 0.02T , dr/dt = 1 mm/s =10-3 m/s
r= 4 cm =4 × 10-2 m , e = ?
φ = BA = B (π r2 )
e= dφ/dt= d/dt (B π r2 )= B π 2 r (dr/dt)
= 0.02 × 22/7 ×2 × 4 ×10-2 × 10-3
= 5× 10-6 V = 5 μV