^Solenoid

Solenoid

Mag. field on the axis of a solenoid is

If solenoid is very long, loops are tight, then for a point situated on the axis & well inside, B = μ₀ nI & for a point near end on the axis,

Field pattern of a long solenoid & a bar magnet are similar, with the difference that magnetic field is maximum at the end of poles where as for a long solenoid it is at centre.