# Current in a soloneid

1. Sep 29, 2005

### jena

Hi,

My Question:

A 50.0-cm long solenoid 1.25cm in diameter is to produce a field of 0.385 T at its center. How much current should the solenoid carry if it has 975 turns of the wire?

I know that I have to use this equation:

B = \mu _0 nI

where i'm stuck at is with the length do I used the how long it is with the diameter or do i just ignore the diameter

Thank You

2. Sep 30, 2005

### mukundpa

1
The formula you have written is for a long solenoid such that L >>R, to insure this, I think the dimeter is given, otherwise you have to use general formula for the field.
2
In this formula 'n' is the number of turns per unit length n = N/L.