The magnetic field in a coil of $100$ turns and $40 \text{ cm}^2$ area is increased from $1 \text{ T}$ to $6 \text{ T}$ in $2 \text{ s}$. The magnetic field is perpendicular to the coil. The $e.m.f.$ generated in it is $...... \text{ V}$.

If a coil of $40$ turns and area $4 \, cm^2$ is suddenly removed from a magnetic field,it is observed that a charge of $2 \times 10^{-4} \, C$ flows through the coil. If the resistance of the coil is $80 \, \Omega$,the magnetic flux density in $Wb \, m^{-2}$ is:

$A$ highly conducting ring of radius $R$ is perpendicular to and concentric with the axis of a long solenoid as shown in the figure. The ring has a narrow gap of width $d$ in its circumference. The solenoid has a cross-sectional area $A$ and a uniform internal magnetic field of magnitude $B_0$. Starting at $t = 0$,the solenoid current is steadily increased such that the field magnitude at any time $t$ is given by $B(t) = B_0 + \alpha t$,where $\alpha > 0$. Assuming that no charge can flow across the gap,the end of the ring which has an excess of positive charge and the magnitude of the induced e.m.f. in the ring are respectively:

The flux linked with a coil at any instant $t$ is given by $\phi = 10t^2 - 50t + 250$. The induced $emf$ at $t = 3 \ s$ is ....... $V$.

Two identical circular loops of metal wire are lying on a table without touching each other. $Loop-A$ carries a current which increases with time. In response,the $loop-B$

$A$ and $B$ are two metallic rings placed at opposite sides of an infinitely long straight conducting wire as shown. If current in the wire is slowly decreased,the direction of induced current will be