Question

but why we have to put magnetic compass made of cork ?why we have to put it in the water?
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Answer 1

Answer:

Although Earth's magnetic field is relatively weak, it should have clearly affected the needle because the needle was allowed to freely float in the cork disk on the water.

Answer 2

Answer:

Although Earth's magnetic field is relatively weak, it should have clearly affected the needle because the needle was allowed to freely float in the cork disk on the water.