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A watch glass filled with a powdered material is kept between the poles of a magnet. A pronounced depression appears at the middle. The material in the watch glass is

1. iron
2. chromium
3. carbon
4. wood

Correct answer: carbon

Solution

Carbon, being a non-magnetic material, does not respond to the magnetic field, leading to the formation of a depression in the powdered material as the magnetic field lines concentrate in the surrounding areas.

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