# Solenoid question

1. Nov 8, 2011

### fisico30

Hello Forum,

How many turns do we need to make a good solenoid? 50, 40 ,1000?

I know the more turns, the larger N, the better. But what is the minimum number of turns to create a homogeneous B field inside the coil and an almost zero B field outside?

Does the cross-sectional area of the solenoid matter, i.e. the diameter of the turns?

I guess the solenoid diameter will determine the strength of the B field inside the solenoid: the smaller the radius of the turns the stronger will be the homogeneous B field?
Thanks
fisico30

2. Nov 8, 2011