What is a solenoid? Provide information about the magnetic field through a qualitative discussion.

(N/A) solenoid is an insulated copper wire wound closely in the form of a helix. $A$ long solenoid is defined as one where the length is very large compared to its diameter.
If its length is shorter than its radius,it is called a short solenoid.
It consists of a long wire wound in the form of a helix where neighboring turns are closely spaced. Thus,each turn can be regarded as a circular loop.
Enamelled wires are used for winding so that turns are insulated from each other.
The net magnetic field is the vector sum of the fields due to all the individual turns.
Figure $(a)$ shows a section of this solenoid in an enlarged manner.
Figure $(b)$ shows the entire finite solenoid with its magnetic field.
In figure $(a)$,it is clear from the circular loops that the field between two neighboring turns cancels out.
In figure $(b)$,we see that the field at the interior midpoint $P$ is uniform,strong,and directed along the axis of the solenoid.
The field at the exterior midpoint $Q$ is weak and directed along the axis of the solenoid with no perpendicular or normal component.
As the solenoid is made longer,it appears like a long cylindrical metal sheet.
The field outside the solenoid approaches zero. We assume that the field outside is zero.
The field inside becomes everywhere parallel to the axis.