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JEE Main202118 Mar 2021Evening ShiftPhysicsAlternating CurrentActual

The time taken for the magnetic energy to reach 25 % of its maximum value, when a solenoid of resistance R , inductance L is connected to a battery, is :

Options

  1. AL R l n 5
  2. Binfinite
  3. CL R l n 2
  4. DL R l n 10

Correct answer

C. L R l n 2

Step-by-step solution

Magnetic energy = 1 2 L i 2 = 25 % M E ⇒ 25 % ⇒ i = i 0 2 i = i 0 1 - R - R t / L for charging t = L R l n 2

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