A straight conductor carrying current is placed in a uniform magnetic field. If the direction of current is reversed while keeping the field unchanged, how will the direction of force on the conductor change?
The force acts in the opposite direction, while its magnitude remains unchanged.
The force on a straight current-carrying conductor in a magnetic field is \(F = BIL\sin\theta\), and its direction is given by Fleming's left-hand rule: the forefinger points along the field, the middle finger along the current and the thumb gives the force.
When the current is reversed with the field unchanged, the middle finger turns the opposite way and so does the thumb. So the force reverses its direction.
The values of B, I, L and the angle between the conductor and the field are all the same in size, so \(BIL\sin\theta\) stays the same and the magnitude of the force does not change. The force does not become zero, since current still flows, and it neither keeps its direction nor becomes larger or smaller.
Hence, The force acts in the opposite direction, while its magnitude remains unchanged.
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