When a magnetic field causes a charged particle to move in a circular path,the only quantity listed below which the magnetic force changes significantly as the particle goes around in a circle is the particle's:
A)energy.
B)momentum.
C)radius for the circle.
D)time to go around the circle once.

Question

Quizplus · Accepted Answer

The magnetic force exerted on a charged particle moving in a magnetic field is given by F = q(v x B), where v is the velocity of the particle and B is the magnetic field. This force is perpendicular to both the velocity and the magnetic field, and thus it causes the charged particle to move in a circular path. 
The radius of the circular path depends on the velocity, mass, and charge of the particle, as well as the strength of the magnetic field. However, the momentum of the particle (p=mv) is conserved in the absence of external forces, and thus it remains constant as the particle moves in a circle. Therefore, the magnetic force does not change the momentum of the particle significantly as it goes around in a circle.

When a Magnetic Field Causes a Charged Particle to Move