At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction.When viewed from a point on the positive z axis, it subsequent motion is:
A)straight ahead
B)counterclockwise around a circle in the xy plane
C)clockwise around a circle in the xy plane
D)in the positive z direction
E)in the negative z direction

Question

Quizplus · Accepted Answer

Since the magnetic field is in the positive z direction and the electron is moving in the positive x direction, the magnetic force acting on the electron will be in the positive y direction due to the cross product of the velocity and magnetic field vectors. This will cause the electron to move in a circular path in the xy plane, with the direction of rotation determined by the right-hand rule. Since the magnetic force is perpendicular to the velocity, the speed of the electron will remain constant as it moves in a circle.

At One Instant an Electron Is Moving in the Positive