$A$ 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:

$A$ uniform but 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. The magnitude of the induced electric field at point $P$ at a distance $r$ $(r > a)$ from the centre of the circular region is:

$A$ uniform magnetic field $B$ exists in a cylindrical region of radius $R = 10 \, cm$ as shown in the figure. $A$ uniform wire of length $L = 80 \, cm$ and resistance $R_{wire} = 4.0 \, \Omega$ is bent into a square frame of side length $a = 20 \, cm$ and is placed with one side along a diameter of the cylindrical region. If the magnetic field increases at a constant rate of $\frac{dB}{dt} = 0.010 \, T/s$,find the current induced in the frame.

$A$ rectangular wire loop of sides $8 \; cm$ and $2 \; cm$ with a small cut is moving out of a region of uniform magnetic field of magnitude $0.3 \; T$ directed normal to the loop. Suppose the loop is stationary but the current feeding the electromagnet that produces the magnetic field is gradually reduced so that the field decreases from its initial value of $0.3 \; T$ at the rate of $0.02 \; T \, s^{-1}$. If the cut is joined and the loop has a resistance of $1.6 \; \Omega$,how much power is dissipated by the loop as heat? What is the source of this power?

An emf can be induced in a stationary coil if it is kept in

In the given figure,the magnetic flux through the loop increases according to the relation $\phi_{B}(t) = 10t^{2} + 20t$,where $\phi_{B}$ is in milliwebers $(mWb)$ and $t$ is in seconds $(s)$. The magnitude of the current through the $R = 2\,\Omega$ resistor at $t = 5\,s$ is $....\,mA$.