A charged particle (mass = M, charge = Q 0) moves in a region of space where the magnetic field has a constant magnitude of B and a downward direction. What is the magnetic force on the particle at an instant when it is moving horizontally toward the north with speed V?
A) QVB toward the east
B) Zero
C) QVB toward the west
D) QVB upward
E) QVB toward the south

Question

A charged particle (mass = M, charge = Q > 0) moves in a region of space where the magnetic field has a constant magnitude of B and a downward direction. What is the magnetic force on the particle at an instant when it is moving horizontally toward the north with speed V?
A) QVB toward the east
B) Zero
C) QVB toward the west
D) QVB upward
E) QVB toward the south

Quizplus · Accepted Answer

The magnetic force on a charged particle moving in a magnetic field is given by the equation F = q(v x B), where q is the charge of the particle, v is its velocity, and B is the magnetic field. The direction of the magnetic force is perpendicular to both the particle's velocity and the magnetic field.

In this case, the particle is moving horizontally toward the north, so its velocity is directly to the west. The magnetic field is directed downward. The cross product of two vectors in the x-y plane gives a vector in the z direction, so the force on the particle will be directed toward the west. Since the particle has a positive charge, and the force on it is negative (directed opposite to its velocity), the force is given by -QVB, or QVB toward the west (choice C).

A Charged Particle (Mass = M, Charge = Q >