A copper wire is wrapped 65 times around an unknown core of length 28cm. The current in the wire is 800mA and the magnetic field due to the electromagnet is 1.63 x 10-2T. What is the most likely material the wire is wrapped around?

1 Answer
Feb 29, 2016

Answer:

Relative permeability #\mu_r# is 689 which is closer to the value for Manganes-Zinc Ferrite. So the core is likely made of Manganese-Zinc Ferrite.

Explanation:

Solenoid: The magnetic field strength #B#, inside a solenoid of length #l# made of #N# number of turns, carrying a current #i# and having a core made of a material with magnetic permeability #\mu=\mu_0\mu_r# is:

#B = \mu(N/l)i#

Given : #B=1.63\times10^{-2}\quad T; \qquad i=0.8\quad A#
#N/l = 65/(28\times10^{-2} \quad m)=232.14m^{-1}#

#\mu = \mu_0\mu_r = \frac{1.63\times10^{-2}\quad T}{(232.14m^{-1})(0.8\quad A)}=8.77\times10^{-5} \quad (T.m)/A#

#\mu_r = \mu/\mu_0 = (8.77\times10^{-5})/(4\pi\times10^{-7})=688.8#

Manganese-Zinc Ferrite has a relative permeability of around 640 (according to wikipedia) . So it could be a Manganese-Zinc Ferrite core. Thanks to Miroslav and A08 for correcting me here.

Magnetic Properties of Materials Reference: https://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29