alleryStart learning →A charge q moves at speed v at an angle theta to a magnetic field of strength B. What is the magnitude of the magnetic force on it?
AF = q/(vB) sin(theta)
BF = qvB sin(theta)
CF = qvB cos(theta)
DF = qv/B sin(theta)
Answer & Solution
Correct answer: B. F = qvB sin(theta)
1. The magnetic force depends on the charge, its speed, the field strength and the angle between v and B.
2. The magnitude is F = qvB sin(theta), with theta measured between the directions of v and B.
3. A sine dependence makes the force zero when the motion is along the field and largest at 90 degrees.
4. A cosine would wrongly give the largest force for motion along the field, where the force is actually zero.
_Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.4 Magnetic Field Strength: Force on a Moving Charge in a Magnetic Field_
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