Induced EMF Questions

A rectangular, a square, a circular and an elliptical loop, all in the $(x-y)$ plane, are moving out of a uniform magnetic field with a constant velocity, $\vec{v}=v\hat{i}$. The magnetic field is directed along the negative $z$ axis. The induced emf will not remain constant for:

A conducting circular loop is placed in a uniform magnetic field $0.04\text{T}$ with its plane perpendicular to the magnetic field. The radius of the loop starts shrinking at $2\text{mm/s}$. The induced emf in the loop when the radius is $2\text{cm}$ is:

A conducting circular loop is placed in a uniform magnetic field, $B=0.025\text{ T}$ with its plane perpendicular to the loop. The radius of the loop is made to shrink at a constant rate of $1{\text{ mms}}^{-1}$. The induced emf when the radius is $2\text{ cm}$ is:

A coil of resistance $400\Omega$ is placed in a magnetic field. If the magnetic flux $\varphi$ (Wb) linked with the coil varies with time $t$ (s) as $\varphi =50t^2+4$, the current in the coil at $t=2\text{s}$ is:

A wire loop is rotated in a magnetic field. The frequency of change of direction of the induced e.m.f. is:

A thin semicircular conducting ring ($PQR$) of radius '$r$ ' is falling with its plane vertical in a horizontal magnetic field $B$. The potential difference developed across the ring when its speed is $v$, is: