# Magnetic flux through a solenoid

quietrain
ok, the magnetic field through a single ring is n$$\mu$$I ,
so the flux is BAcos(theta), with cos(theta)=1, flux = BA = piR2n$$\mu$$I

so why for the entire solenoid flux, it is now nL*the flux above? where L = length of solenoid

shouldn't multiplying it with just n = number of rings be suffice?

also, i don't really understand the magnetic flux. is it define to be the number of field lines per unit area? it is something like density right? so shouldn't it be flux = B/A ? i am getting confused :X

thanks

## Answers and Replies

Those formulas look pretty wrong. The flux should decrease with the length of the coil. And your first formula contains a number n that is not even defined for a single loop (or simply n=1)

Maybe this helps: http://en.wikipedia.org/wiki/Solenoid

quietrain
yup, for a single coil , n = 1.

but i don't understand why for the entire solenoid, we use n*L*dflux/dt = induced EMF

shouldn't just multiplying with n be enough? because n = number of turns. and dflux/dt is for 1 turn. so the entire solenoid just needs to be multiplied by n turns. why do we multiply another length L factor? it is taken from masterphysics.com

quietrain
oh i realise where it all went wrong. after reading the question again for the 3000 time, i realise that n was the number of turns per unit length. so to get N, number of turns, we have to multiply n with L. -.-

sorry for the commotion