Question

A particle of charge +e and mass m moves with speed v perpendicular to a uniform magnetic field B directed into the page. The path of the particle is a circle of radius r, as shown.

Which of the following correctly gives the direction of motion and the equation relating v and r ?

	Direction	Equation
(A)	Clockwise	eBr = mv
(B)	Clockwise	eBr = mv2
(C)	Counterclockwise	eBr = mv
(D)	Counterclockwise	eBr = mv2
(E)	Counterclockwise	eBr2 = mv2

Answer 1

The correct option is: (C)

Explanation:

Pick any small segment of wire. The force should point to the center of the circle. For any small segment of wire, use RHRflat and you get velocity direction is CCW. Equation is the same as the problem above … qvB = mv²/r … eBr = mv.