Question

The radius of the circular conducting loop shown in figure is $R$. Magnetic field is decreasing at a constant rate $\alpha$. Resistance per unit length of the loop is $\rho$. Then current in wire $AB$ is ($AB$ is one of the diameters)

• A. $\frac{R\alpha }{2\rho }$ from B to A
• B. $\frac{R\alpha }{2\rho }$ from A to B
• C. $\frac{2R\alpha }{\rho }$ from A to B
• D. zero

Answer 1

Answer: (D)

As per Lenz’s law, e.m.fs of the same magnitude are induced in the two loops in the clockwise direction. Thus current is induced in the clockwise direction in the outer boundary, but obviously, there is zero current in wire AB.