1. Mar 17, 2005

### vaxopy

$$B = uNI/2L * (L/2/(\sqrt{((L/2)^2)+R^2)} - (-L/2/(\sqrt{((-L/2))^2+R^2))}$$

I get.. $$B = uNI/2R$$ (for those wondering, this is the equation to find the magnetic field when a Hall probe is placed in the center of a solenoid)

they ask me to figure out the % diffeerence between the field at the center of the solenoid compared to a solenoid that infinitely long (where B = uNI)..

I get L = 28cm, R = 2.69cm, I = 1.25A

i get 520% when using my simplified formula >_<
is this right???

and i dont even use the current!

Last edited: Mar 17, 2005
2. Mar 17, 2005

### HallsofIvy

It's hard to tell- you are clearly missing at least one parenthesis. Is the initial
(uNI/2L) multiplied by BOTH fractions (in which case they clearly add) or is it multiplying only the first fraction (which is what you have written- and is much harder).