Question

If the current (I) in a long solenoid is doubled and number of turns per unit length (n) are halved, find the effect on the magnetic field (i) inside and (ii) outside the solenoid.

Answer 1

Solenoid magnetic field

$B=\frac{\mu_0Ni}{L}$

Inside

$B=\mu_0 ni$

$B'=\mu_0n'i'$

$B'=\mu_0\times\frac{n}{2}\times2i$

$\frac{B'}{B}=\frac{1}{1}$

$B'=B$

Part(b)

Out side

$B_o=0T$

Outside magnetic field of solenoid at any point zero

$B_o=0T$