Flux density of solenoid beyond the pole

[Jake110]

I’m making a solenoid and I’m trying to work out how much force it exerts on an object X meters away from it. I’m using F=BIL to get the force but I don’t know the equation for getting the magnetic flux density of the solenoid other than B=(uNI)/L but that’s just for the centre and I need it for outside the solenoid but in line for the object to get pulled towards one of the poles.

Although I’m not sure if B=(uNI)/L is the right equation because the L in that and the L in F=BIL will cancel out when putting them together and it doesn't make sense if the length of the solenoid has no effect on the force it exerts.

 

[Bob S]

For the axial field of a solenoid beyond the end of the coil, look at
http://www.netdenizen.com/emagnet/solenoids/thinsolenoid.htm

 

[Jake110]

yes, that is exactly what i was looking for, thank you.