alleryA magnetic field can do work on a moving charge
AAlways, in proportion to v · B
BNever — F is perpendicular to v, so power F·v = 0
COnly when B is uniform
DOnly when the charge is positive
Answer & Solution
Correct answer: B. Never — F is perpendicular to v, so power F·v = 0
F_mag = qv × B is always perpendicular to v
so P = F·v = 0. Magnetic forces change direction but not speed
they cannot do work on a point charge.
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