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A horizontal solenoid is connected to a battery through a switch. A copper ring is placed on a frictionless track with its axis along the solenoid's axis. When the switch is closed, the ring will:
- remain stationary
- move towards the solenoid
- move away from the solenoid
- move towards the solenoid or away from it depending on which terminal of the battery is connected to the left end of the solenoid.
Correct answer: move away from the solenoid
Solution
When the switch closes, current grows in the solenoid and the magnetic flux through the ring rises. By Lenz's law the ring's induced current opposes this increase, making the ring magnetically equivalent to a like pole facing the solenoid, so it is repelled and moves away. This is independent of battery polarity.
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