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NTA Abhyas JEE Main2020PhysicsElectromagnetic InductionPractice

A solenoid of inductance L and resistance R has a soft iron core. It is connected to a battery of E.M.F E as shown in the figure and allowed to attain its steady state. At an instant, the iron core is suddenly pulled out and because of it, inductance decreases to L 3 . The work done by an external agent in pulling out the iron core is

Options

  1. ALE 2 R 2
  2. B2 LE 2 R 2
  3. CLE 2 2 R 2
  4. DLE 2 4 R 2

Correct answer

A. LE 2 R 2

Step-by-step solution

Flux does not change suddenly. ∴   L 1 I 1 = L 2 I 2 ∴    W = U 2 − U 1 = 1 2 × L 3 × 3 E R 2 − 1 2 × L × E R 2 = 3 E 2 L 2 R 2 − E 2 L 2 R 2 = E 2 L R 2

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