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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.

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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 $0.9999\:\mathrm{N/A}^2$.)

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  • $\begingroup$ Thank you so much. I can't believe I've never seen that before. $\endgroup$ – Ulthran Sep 22 '16 at 1:22
  • $\begingroup$ That is highly nonstandard notation for the relative permeability of the material (unless you can provide sources). The much more usual notation is $\mu_r$. $\endgroup$ – Emilio Pisanty Sep 22 '16 at 1:35
  • $\begingroup$ $\mu_r$ 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) $\endgroup$ – Ulthran Sep 22 '16 at 1:41
  • $\begingroup$ I'm finding conflicting results on the relative permeability of iron (which is what my core is). One site (info.ee.surrey.ac.uk/Workshop/advice/coils/mu/#mur) says for iron that is 99.8% pure it is 5000 while another site (sciencedirect.com/science/article/pii/S001600322890558X) is giving a few other number liek 1150 or 250 $\endgroup$ – Duko Sep 22 '16 at 2:26
  • $\begingroup$ Wait i think I just realized, please confirm. Is mu for the formula 6.28*10^-3. Should I just substitute 6.28*10^-3 into μ in the formula B = μ(N/L)I $\endgroup$ – Duko Sep 22 '16 at 2:35

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