Direction: A coil of inductance 10 H and resistance 40 Ω is connected as shown in the figure. After the switch S has been in contact with point 1 for a very long time, it is moved to poin 2 at t = 0.
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If, at t = 0+, the voltage across the coil is 120V, the value of resistance R is—
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- 0Ω
- 20Ω
- 40Ω
- 60Ω
Correct Option: A
t < 0 connect to 1
| i L(0–) = | = 2 Amp | 20 + 40 |
i L(0–) = i L(0+) = 2 Amp
t = 0+ connect 2
(60 + R) 2 – 120 = 0
60 + R = 60
or R = 0Ω
Hence alternative (A) is the correct choice.
