# What does the constant $(\mu)$ mean in the formula $B=\mu(N/L)I\,?$

In the formula $B=\mu (N/L)I,$ what is the number of the constant $\mu$ for copper? I need to know because I did an experiment where we created an electromagnet and changed the diameter of the wire. We measured the magnetic field using a Pasco sensor. I want to prove this data is correct by manually calculating the strength of the magnetic field. Bear in mind this is year 11 physics so it isn't that complex yet.

In this case, $\mu$ is a stand-in for $\mu_0\,k$. Here $\mu_0$ is a constant $4\pi\times10^{-7}\:\mathrm{T/(A\:m)}$ and $k$ is the relative permeability of the material used for the core of the solenoid.
For example, with Fe, it is around $200\:\mathrm{N/A}^2$. Whatever material your core is, just look up the relative permeability for that substance and multiply by $\mu_0$. That will give you the $\mu$ value in your equation B = $\mu(N/L)I$. (From what I've found $\mu_0$ for Cu is $0.9999\:\mathrm{N/A}^2$.)
• That is highly nonstandard notation for the relative permeability of the material (unless you can provide sources). The much more usual notation is $\mu_r$. – Emilio Pisanty Sep 22 '16 at 1:35
• $\mu_r$ instead of k? I've never actually studied this other than by looking around the internet so I would trust your word over mine. I've always seen it as k though (hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html here for example) – Ulthran Sep 22 '16 at 1:41