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JEE Advanced · 2012 · 08 Apr 2012 · Paper 2 · Electromagnetic Induction

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A current carrying infinitely long wire is kept along the diameter of a circular wire loop, without touching it. The correct statement(s) is(are)
  1. (A)The emf induced in the loop is zero if the current is constant.✓ Correct
  2. (B)The emf induced in the loop is finite if the current is constant.
  3. (C)The emf induced in the loop is zero if the current decreases at a steady rate.✓ Correct
  4. (D)The emf induced in the loop is finite if the current decreases at a steady rate.

Answer: (A), (C)

Solution

The magnetic field due to an infinitely long straight wire forms concentric circles around the wire. When the wire is along the diameter of the circular loop, the magnetic flux through the loop is zero by symmetry—the flux through one half of the loop is equal and opposite to the flux through the other half. Since always (regardless of the current), , and therefore the induced emf is zero whether the current is constant or changing.

JEE Advanced · 2012 · 08 Apr 2012 · Paper 2 · One or more correct options

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