The figure shows a circular area of radius $R$ where a uniform magnetic field $\vec B$ is directed into the plane of the paper and is increasing in magnitude at a constant rate. In this case,which of the following graphs,drawn schematically,correctly shows the variation of the induced electric field $E(r)$ with distance $r$ from the center?

$A$ time-varying magnetic field $B(t)$ exists in a circular region of radius '$a$' and is directed into the plane of the paper,as shown in the figure. The magnitude of the induced electric field at a point '$P$' at a distance '$r$' $(r > a)$ from the center of the circular region is:

$A$ magnetic field in a certain region is given by $\vec B = B_0 \cos(\omega t) \hat k$. $A$ coil of radius $a$ with resistance $R$ is placed in the $xy$-plane with its centre at the origin in the magnetic field (see figure). Find the magnitude and the direction of the current at $(a, 0, 0)$ at $t = \frac{\pi}{2\omega}$,$t = \frac{\pi}{\omega}$,and $t = \frac{3\pi}{2\omega}$.

$A$ uniform magnetic field $B$ exists in a cylindrical region of radius $10\,cm$ as shown in the figure. $A$ uniform wire of length $80\,cm$ and resistance $4.0\,\Omega$ is bent into a square frame and is placed with one side along a diameter of the cylindrical region. If the magnetic field increases at a constant rate of $0.010\,T/s$,find the current induced in the frame.

$A$ short-circuited coil is placed in a time-varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire radius halved, the electric power dissipated would be .............

$A$ non-conducting ring (of mass $m$,radius $r$,having charge $Q$) is placed on a rough horizontal surface in a region with a transverse magnetic field. The magnetic field is increasing with time at a rate $R = dB/dt$. If the coefficient of friction between the surface and the ring is $\mu$,for the ring to remain in equilibrium,$\mu$ should be greater than: