A tightly wound solenoid of radius 'a' and length 'l' has 'n' turns per unit length.It carries an electric current 'i'.Consider a length 'dx' of the solenoid at a distance 'x' from one end.This contains 'ndx' turns and may be approximated as a circular current 'indx'

(a)Write the magnetic field at the centre of the solenoid due to this circular current.Integrate this expression under proper limits to find the magnetic field at the centre of the solenoid.

(b)Verify that if l>>a,the field tends to B=u₀ni and if a>>l,the field tends to B=u₀ni/2a.

ANS:-(a)u₀ni/[1+(2a/l)²]^1/2 

HURRY UP............

find out the magnetic field due 2  the which is at a distance l/2 - x frm center and then integrate it frm `0` to `l`..

use the formula for field at an axial pt.... replace i by indx and d by l/2 - x.......... and then integrate u wil get the answer....