Assertion : The density of field lines decreases in a medium of high permeability

Reason : Because $B\propto \frac{1}{\mu }$

A uniform but time varying magnetic field $B\left(t\right)$ exists in a.circular region of radius $a$ it is directed into the plane of the paper as shown. The magnitude of the induced electric field at point $P$ at a distance $r$ from the centre of the circular region.

Assertion: A resistance $R$ is connected between the two ends of the parallel smooth conducting rails. A conducting rod lies on these fixed horizontal rails and a uniform constant magnetic field $B$ exists perpendicular to the plane of the rails as shown in the figure. If the rod is given a velocity $v$ and released as shown in the figure, it will stop after some time. The total work done by the magnetic field is negative.

Reason: In this case, the resultant magnetic force on the free charges is opposite to the velocity of the free charges.

The galvanometer deflection. when key $K_1$ is closed but $K_2$ is open equals ${\theta }_0$ (see figure). On closing $K_2$ also and adjusting $R_2$ to $5 \mathrm{\Omega }$, the deflection in galvanometer becomes $\frac{{\theta }_0}{5}$.

The resistance of the galvanometer is given by (neglect the internal resistance of battery) :