I keep getting “Magnetic force on a moving charge” questions wrong in Magnetism & Electromagnetic Induction. What's the trap?
thinking the magnetic force can speed a charge up.
The usual trap: thinking the magnetic force can speed a charge up. How to avoid it: a magnetic force does zero work — it only bends the path. Go back to the definition — F = qvB·sinθ, always perpendicular to the velocity, so it changes direction but not speed.
Key point
Magnetic force on a moving charge
Common mistake
thinking the magnetic force can speed a charge up.
Memory tip
a magnetic force does zero work — it only bends the path.
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