A solid copper disk of radius R rotates at angular speed ? in a perpendicular ma

Question

A solid copper disk of radius R rotates at angular speed ? in a perpendicular magnetic field B. The figure below shows the disk rotating clockwise and the magnetic field directed into the screen.

(a) Is the charge that accumulates on the edge of the disk positive or negative? Briefly explain why.

(b) What is the potential difference between the center of the disk and the edge? (Use the following as necessary: R, B, ?.) [Hint: Think of the disk as a large number of thin wedge-shaped rods. The center of such a rod is at rest, and the outer edge moves at speed v = ?R. The rod moves through a perpendicular magnetic field at an average speed of ?R.]

V=

Explanation / Answer

a) Charge accumulating on edge of disk is positive Since Force is qV*B v*b is always pointing in radial direction so positive charge experiences an outward radial force so a positive charge accumulates on edge of disk. b) We know V=Blv dV=BLv=Bdxwx V=BwR^2/2

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