The network shown, if iR = (4 e— 3t + 5 e

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The network shown, if i_R = (4 e^{— 3t} + 5 e^{— 4t}) amp and i _L (0) = 15 amp, then at t = 0 φ would be equal to—

1. π
  2
2. π
  3
3. 2π
  3
4. 2 π

Correct Option: B

From given figure
I_L = I_R + I₂ cos (t – φ)
15 = (4e^–3t + 5e^–4t) + 12 cos (t – φ)
at t = 0
15 = 4 + 5 + 12 cos (–φ)
or 15 – 9 = 12 cos φ
or 6 = 12 cos φ

or cos φ =	1
	2

or φ =	π
	3