When a straight conductor of fixed length is placed in a uniform magnetic field and the current through it is doubled, the force on the conductor also doubles. Which of the following underlying principles explains this proportional relationship?
The force is directly proportional to the current
The force on a straight current-carrying conductor in a uniform magnetic field is \( F = BIL\sin\theta \), where B is the field strength, I the current, L the length and θ the angle between conductor and field.
With B, L and θ fixed, F ∝ I. So doubling the current doubles the force — exactly the relationship described.
The field direction (Fleming's left-hand rule) fixes only the direction of the force, the length is held constant here, and an inverse relation would halve the force instead of doubling it.
Hence, the answer is: The force is directly proportional to the current.
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