Magnetism and Electromagnetism
A permeable substance is one

which is a good conductor
which is a bad conductor
which is a strong magnet
through which the magnetic lines of force can pass very easily

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Magnetism and Electromagnetism
Main causes of noisy solenoid are

Both of the listed here
uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
None of these
strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force

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