Magnetism and Electromagnetism
For a given wirewound core, an increase in current through the coil

decreases the flux density
reverses the flux lines
causes no change in flux density
increases the flux density

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Magnetism and Electromagnetism
Main causes of noisy solenoid are

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

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