When a wire loop is rotated in a magnetic field,the direction of induced $emf$ changes in every

When a rectangular coil is rotated in a uniform magnetic field about an axis passing through its centre and perpendicular to the field,the emf induced in the coil varies

$A$ ring of resistance $10 \Omega$,radius $10 \text{ cm}$,and $100$ turns is rotated at a rate of $100$ revolutions per second about a fixed axis which is perpendicular to a uniform magnetic field of induction $10 \text{ mT}$. The amplitude of the current in the loop will be nearly $A$ (Take $\pi^2 = 10$).

In a uniform magnetic field of induction $B$,a wire in the form of a semicircle of radius $r$ rotates about the diameter of the circle with angular frequency $\omega$. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is $R$,the mean power generated per period of rotation is

$A$ rectangular coil of $300$ turns has an average area of $25\;cm \times 10\;cm.$ The coil rotates with a speed of $50\;cps$ in a uniform magnetic field of strength $4 \times 10^{-2}\;T$ about an axis perpendicular to the field. The peak value of the induced $e.m.f.$ is (in volt): (in $\pi$)

$A$ circular coil of mean radius $7 \, cm$ and having $4000$ turns is rotated at the rate of $1800$ revolutions per minute in the earth's magnetic field $(B = 0.5 \, \text{gauss})$. The maximum $e.m.f.$ induced in the coil will be .... $V$.