Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

In a question:

To construct a solenoid, you wrap insulated wire uniformly around a plastic tube 12cm in diameter and 50cm in length. You would like a 2.2 A current to produce a 2.6 kG magnetic field inside your solenoid.

What is the total length of wire you will need to meet these specifications?

In the provided answer:

$$NC = nL C = (\frac{B}{\mu_0 I}) L (\pi d)$$


  • $N$ is total number of turns
  • $n$ is number of loops
  • $C$ is circumference

But I dont understand why is there an $L$

I did it by:

$$B = \mu_0 n I$$

Then length of wire needed is just $nC$ whats wrong?

share|cite|improve this question

$n$ in this case isn't the number of loops, it's the number of loops per unit length. This is why you have to multiply it by $L$ to get $N$.

share|cite|improve this answer
True. Our professor stressed on this point a lot, so that we wouldn't make a mistake. :) – mikhailcazi Jun 25 '13 at 12:14

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.