An emf of 20   V is applied at time t = 0 to a circuit containing in series 10   m H inductor and…

An emf of 20 V is applied at time t=0 to a circuit containing in series 10 mH inductor and 5 Ω resistor. The ratio of the currents at time t=∞ and at t=40 s is close to: (Take e2=7.389 )
  1. 1.06
  2. 1.15
  3. 1.46
  4. 0.84

Solution

i=i01-e-tL/R

=2051-e-t0.01/5
=41-e-500t

now at t=∞
i∞=4

at t=40 s
i40=41-e-500×40
=41-1e210000=41-17.2910000
i∞i40≈1 Slightly greater then one.

Asked in: JEE Main 2020 (07 Jan Shift 2)

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