# Find the magnetic permeability of the iron bar.

#### zade70

1. The problem statement, all variables and given/known data
In a solenoid with 12 enamels for cm passes the current 2 A. Find the magnetic permeability of the iron bar inside it.(B0=1.508 T)

2. Relevant equations
B=μ0*I*N/l(length)

3. The attempt at a solution
We have N/l(length)=1200 enamels/meter
B=4*10^-7*3.14*25*1200=0.003T
Now μr(relative permeability)(if this is what the problem is asking is B/B0=1/500, but in my book it is 500. Where is the error?

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#### marcusl

Science Advisor
Gold Member
You have swapped B0 and B.

#### zade70

You have swapped B0 and B.
I found that B=0.003, in the book B0=1.508. μr=B/B0=0.003/1.508=1/500. Where did I make the mistake?

#### marcusl

Science Advisor
Gold Member
B0 is usually used to indicate field in a vacuum and B is the field in the material. B0=.003 and B=1.5, so mu=500.

#### zade70

B0 is usually used to indicate field in a vacuum and B is the field in the material. B0=.003 and B=1.5, so mu=500.
But in this case B0=1.5 T(I found out) and B=1.5 T (given by the book)

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