A charged particle is moving in a uniform, constant magnetic field. Which one(s) of the following statements concerning the magnetic force exerted on the particle is not true? (Mark all that are not true.)
It may change the velocity of the particle.
It does no work on the particle.
It does not change the kinetic energy of the particle.
It may increase the speed of the particle.

Question

A charged particle is moving in a uniform, constant magnetic field. Which one(s) of the following statements concerning the magnetic force exerted on the particle is not true? (Mark all that are not true.)
	It may change the velocity of the particle.
	It does no work on the particle.
	It does not change the kinetic energy of the particle.
	It may increase the speed of the particle.

anonymous · Answer

it does some work on the particle. Work = force * distance, quite obvious, isn't it?
the velocity is surely changed! Magnetic fields basically make your particle moves in a circle in this case. Velocity = magnitude+direction. Magnitude doesn't change since it moves in a circle, however, the direction does changed! So there is a change in v. Kinetic energy is a scalar value, so it doesn't changed. Why? because K= 1/2 mv^2, K is a scalar quantity, vector* constant = vector, not scalar. So you're using speed for K, not velocity. K doesn't change because speed is unchanged (only direction). Hope you can understand it conceptually, and reason it out! :) Good luck

esraa · Answer

This is really helpful, thnx again