alleryStart learning →A straight wire of length l carries current I in a uniform field B, at an angle theta between the current and the field. What is the magnetic force on it?
AF = Il/B sin(theta)
BF = I/(lB) sin(theta)
CF = IlB sin(theta)
DF = IlB cos(theta)
Answer & Solution
Correct answer: C. F = IlB sin(theta)
1. Each moving charge in the wire feels a force qvB sin(theta), and all these forces add.
2. Summing them over the length of wire in the field gives F = IlB sin(theta).
3. Here I is the current, l is the length inside the field and theta is the angle between the current and the field.
4. A cosine form would give maximum force for a wire lying along the field, where the force is really zero.
_Source: OpenStax College Physics (CC BY 4.0), Ch 22 "Magnetism", section 22.7 Magnetic Force on a Current-Carrying Conductor_
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