A metal disc rotates freely between the poles | vedclass

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(B) When a metal disc rotates in a uniform magnetic field perpendicular to its plane,a motional electromotive force $(emf)$ is induced between the cen

Vedclass · Accepted Answer

$A$ current from $Q$ to $P$.

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(B) When a metal disc rotates in a uniform magnetic field perpendicular to its plane,a motional electromotive force $(emf)$ is induced between the center and the rim of the disc.According to the Lorentz force law,the force on the free electrons in the rotating disc is given by $\vec{F} = q(\vec{v} 	imes \vec{B})$.For a disc rotating with angular velocity $\omega$ in a magnetic field $\vec{B}$ directed into the page,the velocity $\vec{v}$ of a charge carrier at a distance $r$ from the center is tangential. The resulting force pushes electrons toward the center $(P)$ and positive charges toward the rim $(Q)$.This creates a potential difference between the center and the rim,acting like a battery. Consequently,a current flows through the external resistance $R$ from the rim $(Q)$ to the center $(P)$.

$A$ metal disc rotates freely between the poles of a magnet in the direction indicated. Brushes $P$ and $Q$ make contact with the center (axle) and the edge of the disc,respectively. What current,if any,flows through $R$?

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