Question

magnetic field is uniform inside the solenoid why​

Answer 1

at various points of the solenoid current enters the plane of paper and leaves the plane of paper at another. The magnetic field at point close to the single turn of the solenoid is in the form of concentric circles like that of a straight current carrying wire. the resultant field of the solenoid is a vector sum of the field due to all the terms of the solenoid .obviously the field due to the neighbouring turns adds up along the axis of the solenoid but they cancel out in the perpendicular direction . Thus the field at interior points is uniform and strong .