A solenoid is a device used to generate a homogeneous magnetic field. It can be made of a thin conducting wire wound in a tight helical coil of many turns. The magnetic field inside a solenoid can be determined by summing the magnetic fields generated by the all individual rings.
Where L is the horizontal length of the integration path. The current enclosed by the integration path is equal to N I0 where N is the number of turns enclosed by the integration path and I0 is the current in each turn of the solenoid. Using Ampere's law we conclude that,
\[\int _{ABCD}BdL=BL=\mu _{0}Ni\]
\[B=\mu _{0}\frac{N}{L}i=\mu _{0}ni\]
where n is the number of turns of the solenoid per unit length. The magnetic field B is independent of the position inside the solenoid and the magnetic field inside an ideal solenoid is uniform.
