# Calculating the magnetic field in solenoid

1. Feb 27, 2013

### rp8308

Just need a question cleared up.

If I had a coil wrapped around a core, and I was calculating the magnetic field of the solenoid using

B = μnI

where n = N/L, I is current and μ is the permeability of my material

N being the number of turns in the coil, and L being the length of the solenoid if there was an air core. Now if I had a steel core, for example, and the core was a large circular shape such that the coil itself only wrapped around a small amount of the core. Would the length L be the length of the solenoid still? (because its defined as turn density) or would it be the length that the magnetic flux takes through the whole core and therefore be the mean length of the core? (much larger than the length of the solenoid).

Cheers

2. Feb 27, 2013

### rp8308

ok I am pretty sure its the length of core because flux through the core won't change with the density of turns, but could do with someone just confirming this... I hate when i confuse myself

Last edited: Feb 27, 2013
3. Feb 27, 2013

### BruceW

If you meant to say L is the length of the coil, then yes I agree.

Edit: By 'length of the coil' I mean the length of the core which is surrounded by coil. (Not the actual length of the coil which is wrapping around it).