The magnetic flux linked with a coil varies as $\phi=3 t^2+4 t+9$. The magnitude of the emf induced at $t=2 \mathrm{~s}$ is

A step-up transformer operates on a 230 V "ne and a load current of 2 A . The ratio of primary and secondary windings is $1: 25$. Then, the current in the primary is

The working of magnetic braking of trains is based on

A bar magnet is allowed to fall vertically through a copper coil placed in a horizontal plane. The magnet falls with a net acceleration, is