# Homework Help: Inductance Of A Solenoid Problem!

1. Feb 22, 2012

### pierretong

1. The problem statement, all variables and given/known data

A solenoid is wound with a single layer of insulated copper wire of diameter 2.100 mm and has a diameter of 3.000 cm and is 1.900 m long. Assume that adjacent wires touch and that insulation thickness is negligible.

a) How many turns are on the solenoid?
Solved: determined to be 904

b)What is the inductance per meter (H/m) for the solenoid near its center?

2. Relevant equations

Inductance = (constant mu0)* (N^2)*A / l

mu0 = 4*PI*10^-7
N = 904 turns
A = PI*R^2 (R = 2.100 mm/2)
l = length of solenoid = 1.900 m

3. The attempt at a solution

Plugged all those variables above (converted R to meters) and got 0.00019 for the inductance.

I don't understand what it means to find the Inductance per Meter at the center of the solenoid? Do I have to divide by 1.900 m again? Confused as to what I'm supposed to do.

2. Feb 25, 2012

### tiny-tim

hi pierretong!
yes, your formula µN2A/l gives the inductance of the whole solenoid

so divide by l again for the inductance per metre

(if you cut the solenoid into x pieces, then for one piece N2 would be 1/x2, so N2/l would be 1/x)