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
strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force
None of these

ANSWER DOWNLOAD EXAMIANS APP

Magnetism and Electromagnetism
In a simple magnetic field the strength of magnet flux

decreases continuously from initial value to final value
is constant and has same value in energy part of the magnetic field
increases continuously from initial value to final value
first increases and then decreases till it becomes zero

ANSWER DOWNLOAD EXAMIANS APP