Question

The current in an inductor is given by i = 2 + 3tamp where t is in second. The self induced emf in it is 9 mV the energy stored in the inductor at t= 1 second is

• A. 10 Mj
• B. 37.5 Mj
• C. 75 Mj
• D. Zero

Answer 1

Answer: (B)

37.5 Mj

Answer 2

At t = 1 sec, i = 2 + 3 × 1 = 5A and $|e| = L\frac{di}{dt}$ ⇒ 9 × 10^–6 $= L \times \frac{d}{dt}(2 + 3t)$ ⇒ L = 3 × 10^–3 H

So energy $U = \frac{1}{2}Li^{2} = \frac{1}{2}(3 \times 10^{- 3}) \times (5)^{2}$ = 37.5 mJ.