1. A proton enters a uniform magnetic field that is perpendicular to the proton's velocity (Fig. 20-51).What happens to the kinetic energy of the proton?
(a) It increases.
(b) It decreases.
(c) It stays the same.
(d) It depends on the velocity direction.
(e) It depends on the B field direction.

2. For a charged particle, a constant magnetic field can be used to change
(a) Only the direction of the particle's velocity.
(b) Only the magnitude of the particle's velocity.
(c) Both the magnitude and direction of the particle's velocity.
(d) None of the above.