Question

A charged particle moves in a magnetic field. The only force influencing the particle is the force caused by the magnetic field.
During the particle's movement in the magnetic field, what will NOT change?

• A. the particle's velocity
• B. the particle's acceleration
• C. the particle's speed
• D. the particle's momentum
• E. the particle's position

Answer 1

Answer: (C)

the particle's speed

"From Newton's second law of motion, we know that when an object experiences a net force, the object will accelerate in the direction of that net force. Since the only force acting on the particle is the force exerted by the magnetic field, this magnetic field force must be the net force.

Forces by magnetic fields on moving charged particles always act in a direction that is perpendicular to the velocity of the particle, meaning that they will never change the speed of the particle.

Since in this case the particle is experiencing a net force, the particle must be accelerating.

All of the vector quantities here are constantly changing since the particle is constantly changing direction.

The velocity direction is changing, the acceleration direction is changing, the momentum direction is changing along with the velocity, and the position is obviously changing.

The particle's speed does not change therefore option "C" is right.