A wheel of 20 metallic spokes each 40 cm long is rotated with a speed of $180 \mathrm{rev} / \mathrm{min}$ in a plane normal to the horizontal component of earth's magnetic field $H_c$ at a place. If $H_c=0.4 \mathrm{G}$ (Gauss) at that place, the induced emf between the axle and the rim of the wheel is

A metal disc of radius 30 cm rotates with a constant angular velocity $\omega=100 \mathrm{rad} / \mathrm{s}$ about its axis. Find the magnitude of potential difference between the centre and the rim of the disc of the external uniform magnetic field on induction $B=4 \mathrm{mT}$ is directed perpendicular to the disc.

The magnetic flux through the triangular loop shown in the figure below

Where a uniform magnetic field of strength 2 T points perpendicularly into the plane of the triangle is

A wire loop of area $0.2 \mathrm{~m}^2$ has a resistance of $20 \Omega$. A magnetic field pointing normal to the loop has a magnitude of 0.25 T and is reduced to zero at a uniform rate in $10^{-4} \mathrm{~s}$. What is induced emf and resulting current?