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NCERT Class XII Chapter
Electromagnetic Induction
Questions With Solutions

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Question : 11
Total: 17
Suppose the loop shown in figure is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that field decreases from its initial value of 0.3 T at the rate of 0.02 T s–1. If the cut is joined and the loop has a resistance of 1.6 W, how much power is dissipated by the loop as heat? What is the source of this power?
Solution:  
Here area is constant but the magnetic field is reducing at a constant rate
dB
dt
 = - (0.02) T s−1
Area of the loop, A = l × b = 8 × 2 cm2 = 16 cm2 = 16 × 10–4m2
Induced emf in the loop
ε = -
dϕ
dt
 = - A
dB
dt
ε = - 16 × 10−4 [- 0.02] = 32 × 10−6 V
Induced current in the closed loop
I = ε/R =
32×10−6
1.6
 = 20 µA
Power loop as heat P = I2 R
P = (20×10–6)2 × 1.6 = 6.4 × 10–10 W
Source of the power is work done in changing magnetic field.
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