$A$ rectangular metallic loop is moving out of a uniform magnetic field region to a field-free region with a constant speed. When the loop is partially inside the magnetic field,the plot of the magnitude of induced $\text{emf} \ (\varepsilon)$ with time $(t)$ is given by:

$A$ jet plane having a wing span of $25 \ m$ is travelling horizontally towards the east with a speed of $3600 \ km/h$. If the Earth's magnetic field at the location is $4 \times 10^{-4} \ T$ and the angle of dip is $30^{\circ}$,then the potential difference between the ends of the wing is: (in $V$)

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

$A$ circular coil of radius $30 \ cm$,having $1$ turn and a resistance of ${\pi ^2} \ \Omega$,is placed in a magnetic field of $10^{-2} \ T$. The coil rotates about its diameter with a speed of $200 \ rpm$ in a direction perpendicular to the magnetic field. The value of the induced $AC$ current in the coil will be . . . . . . $mA$.

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

What is motional $emf$?