alleryThe work done by a static magnetic force on a moving charge is:
AAlways positive
BAlways zero
CAlways negative
DDepends on the trajectory
Answer & Solution
Correct answer: B. Always zero
1. F_mag = q v × B is ALWAYS perpendicular to v.
2. So F · v = 0 ⇒ no work done by magnetic force.
3. Magnetic force can change the DIRECTION of v but not its speed (and hence not its KE).
_Source: syllabus Physics Ch 4 §4.2 Work by Magnetic Force_
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