Magnetic flux passing through a coil is initially $4 \times 10^{-4} \ Wb$. It reduces to $10 \%$ of its original value in $t$ seconds. If the induced emf is $0.72 \ mV$,then $t$ in seconds is:

$A$ metal ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is

$A$ circular coil has $100$ turns,radius $3 \ cm$ and resistance $4 \Omega$. This coil is co-axial with a solenoid of $200$ turns/cm and diameter $4 \ cm$. If the solenoid current is decreased from $2 \ A$ to zero in $0.04 \ s$,then the current induced in the coil is

The flux associated with a closed loop is $\phi = 3t^2 + 2t + 5 \text{ Wb}$. If the resistance of the loop is $14 \ \Omega$,then the current induced in this coil at $t = 2 \text{ s}$ is . . . . . . . (in $\text{ A}$)

An electric generator is based on . . . . . .

$A$ magnetic field $4 \times 10^{-2} \, T$ acts at right angles to a coil of area $100 \, cm^2$ with $50$ turns. The average e.m.f. induced in the coil is $0.1 \, V$, when it is removed from the field in time '$t$'. The value of '$t$' is