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An electron moves east in a magnetic field directed north. The magnetic force on the electron points
Adirected up
Bdirected down
Cdirected east
Dzero
Answer & Solution
Correct answer: B. directed down
1. The magnetic force on a charge is F = qv × B.
2. Take east as +x, north as +y, up as +z. Then v × B = x̂ × ŷ = ẑ (upward).
3. For a positive charge, the force would be upward; for the electron (charge -e), the force flips direction.
4. So the magnetic force on the electron points downward.
_Source: NCERT Class 12 Physics Ch 4 "Moving Charges and Magnetism", §4.2.2_
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