In: Physics
An ideal solenoid holds a current ?. Use Ampere’s Law to show that the magnetic field strength inside the solenoid is ?=?0??.
n = number of turns per unit length
L = length considered
I = total current
consider a ampere's closed loop PQRS
B. dl = B. dl Cos0 = B L
B. dl = B. dl Cos90 = 0
B. dl = (0). dl = 0
B. dl = B. dl Cos90 = 0
So
B.dl = B. dl + B. dl + B. dl + B. dl
B.dl = BL + 0 + 0 + 0
B.dl = BL
according to ampere's law
B.dl = NI
So
BL = NI
B = (N/L)I
B = (n)I