Electromagnetic Induction

Number of turns, N=45
Radius, r=4cm=0.04m
Change in magnetic field, ∆B=0.70T−0=0.70T
Time interval, ∆t=220s
The plane of the coil is perpendicular to the magnetic field, so flux is maximum.
Step 1: Rate of change of magnetic field
‌

dB

dt

=‌

0.70

220

=3.18×10−3T∕s
Step 2: Area of the coil
A=πr2=π(0.04)2=π×1.6×10−3=5.027×10−3m2
Step 3: Induced emf (Faraday's law)
ε=NA‌

dB

dt

Substitute values:
‌ε=45×5.03×10−3×3.18×10−3
‌ε=45×1.6×10−5=7.2×10−4V
‌ε=0.72mV