# Homework Help: Self inductance formula question

1. Aug 28, 2009

### nabliat

2. Aug 28, 2009

### gabbagabbahey

$A$ is the cross sectional area of the solenoid/telephone cord, and the magnetic field inside the solenoid is $B=\mu_0 NI/l$ so the flux through one loop in the solenoid is $BA=\mu_0 N IA/l$ so the total flux is $\Phi= \mu_0 N^2 I A/l$ and the inductance is just total flux divided by current.

3. Aug 28, 2009

thanks