The ways by which the magnetic field of the solenoid can be made stronger are:
The number of turns of the solenoid is increased.
The current passing through the coil is increased
A solenoid is a series of circular loops in the form of a helix, as shown in the figure above. The magnetic field lines around the solenoid are similar to the field lines around a bar magnet. The strength of the solenoid can be increased by increasing the number of turns or by increasing the current flowing through it. However, the length of the solenoid and density of the coil do not affect the strength of the magnetic field.