A copper rod of length $l$ is rotated about one end perpendicular to a uniform magnetic field $B$ with constant angular velocity $\omega$. The induced emf between the ends of the rod is $\epsilon$. If the length of the rod is doubled and the angular velocity is halved, the new induced emf will be:

A metal conductor of length ${\rm{1 m}}$ rotates vertically about one of its ends at angular velocity $5\,\,rad\,\,{{\rm{s}}^{ - 1}}$. If the horizontal component of earth’s magnetic field is $0.2\,\, imes {10^{ - 4}}\,{\rm{T}}$, then the emf developed between the two ends of the conductor is

A square aluminum plate is held stationary above a strong bar magnet. Under what condition would a force be required to maintain its position?

For a coil having L = 2 mH, current flows at the rate of ${10^3}\;{\rm{A}}{{\rm{s}}^{ - 1}}$. The emf induced is

A metal of radius ${\rm{100}}\,\,{\rm{cm}}$ is rotated at a constant angular speed of ${\rm{60}}\,\,{\rm{rad}}{{\rm{s}}^{ - 1}}$ in a plane at right angles to an external field of magnetic induction ${\rm{0}}{\rm{.05}}\,\,{\rm{Wb}}{{\rm{m}}^{ - 2}}$. The emf induced between between the centre and a point on the rim will be

A long horizontal metallic rod with length along the east-west direction is falling under gravity. The potential difference between its two ends will

The unit of motional emf is:

The length of a potentiometer wire is 1 m and its resistance is $4\,\Omega$. A current of $5\,mA$ is flowing in it. An unknown source of emf is balanced on $40{\mkern 1mu} \,cm$ length of this wire, then find the emf of the source.

An inductor having coefficient of self induction ${\rm{40}}\,\,{\rm{mH}}$. What is the energy stored in it when a current of ${\rm{2 A}}$ is passed through it?

The magnetic field in a coil of ${\rm{100}}$ turns and $40{\mkern 1mu} {\mkern 1mu} \,square\,\,cm$ area is increased from $1\,\,tesla$ to $6\,\,tesla$ in $2\,\,seconds$. The magnetic field is perpendicular to the coil. The e.m.f. generated in it is

Armature current in dc motor will be maximum when