If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity?
Correct answer: D. less than that of disc and in the same direction
- A. less than that of disc but in opposite direction
- B. equal to that of disc and in the same direction
- C. equal to that of disc and in the opposite direction
- D. less than that of disc and in the same direction
Explanation
The rotating copper disc produces eddy currents whose magnetic field opposes the relative motion of the needle. The needle is therefore dragged in the same direction as the disc, but at a lower speed.
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