Assertion (A) When a circular coil. placed in a region with its place parallel to a magnetic field, expands…

Assertion (A) When a circular coil. placed in a region with its place parallel to a magnetic field, expands radially outwards, no emf is induced in it. Reason (R) There is a constant magnet field in the perpendicular (to the plane of the coil) direction.
  1. Both $A$ and $R$ are true. $R$ is correct explanation of $A$.
  2. Both $A$ and $R$ are true. $R$ is not correct explanation of $\mathrm{A}$.
  3. $A$ is true, $R$ is false.
  4. A is false, $R$ is true.

Solution

When plane of a coil is parallel to magnetic field,
Flux linked with coil, $\phi_B=\mathbf{B} \cdot \mathbf{A}=0 \quad(\mathbf{B} \perp \mathbf{A}=0)$ So induced emf is zero. $\therefore$ Assertion A is correct. Reason $\mathrm{R}$ is incorrect as magnetic field is parallel to the plane of coil.

Asked in: AP EAMCET 2022 (07 Jul Shift 2)

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