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 a 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 a 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 experienced by a charged particle moving in a magnetic field is given by F = QVBsinθ, where Q is the charge of the particle, V is its velocity, B is the magnitude of the magnetic field, and θ is the angle between the velocity vector and the magnetic field vector. Since the particle is moving horizontally toward the north, its velocity vector is perpendicular to the magnetic field vector. Therefore, the angle between the velocity vector and the magnetic field vector is 90° and sinθ = 1. The magnetic force on the particle is F = QVBsinθ = QVB. Since the charge of the particle is positive, the direction of the magnetic force is given by the right-hand rule, which predicts that the force will be perpendicular to both the velocity vector and the magnetic field vector, pointing toward the west. Therefore, the correct answer is C.

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