# Need help with permeability of free space.

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1. Apr 6, 2017

### bory2eye

1. The problem statement, all variables and given/known data
In a lab that I did in Physics we calculated the magnetic field of a solenoid while constantly increasing the number of time the wire was wrapped around the electromagnet. After I obtained all the values, plotted it in a graph and found the line of best fit, the slope came out to be 0.0027*10^-3. I learned that the slope in an N vs. B graph is the permeability of free space multiplied by the current. The current was set to one and I made sure with an Ammeter. I am concerned that my calculated value of the permeability of free space is more than double of the actual constant, 4*pi*10^-6.

2. Relevant equations
B = 0.0027*10^-3N + 0.0906

3. The attempt at a solution
I tried justifying with the sensor picking up the magnetic field of the Earth as well, or magnetization of the solenoid but I can't seem to be obtaining the right justification.

2. Apr 6, 2017

### TSny

Hello, welcome to PF!

The usual interpretation of "N vs. B graph" is a graph with N plotted on the vertical axis and B plotted on the horizontal axis. Is this how you plotted your graph?

Does your symbol N stand for the total number of turns (wraps) of wire, or does it stand for the number of turns per unit length?

Can you state the "theoretical formula" for the magnetic field that shows how B depends on the current and other properties of the solenoid?

Typo: the permeability of free space is 4π*10-7 Tm/A.