# Ampere's Law

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Hello everybody,

The Ampere's Law states that the total $B$-field generated by a conducting element of length $l$ is directly proportional to the current element $I$.

Thus,

$Bl = \mu_0 I$

Where $\mu_0$ is the constant of proportionality.

But, will the constant of proportionality be $\mu_0$ or $\mu_0 \mu_r$ ?

These two sites use two different formulations.....

http://www.electrical4u.com/biot-savart-law/

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c1

Edited by Sriman Dutta

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Both are right!

The Biot-Savart page is simply more complete in that it takes into account the medium via ${\mu _r}$

For air and many purposes such as the space between sub atomic particles ${\mu _r}$ is so close to 1 that we often ignore it.
A more satisfactory way to deal with this is to use
$\mu = {\mu _0}{\mu _r}$
Then there is no ambiguity.
Incidentally your hyperphysics link has some good pictures of the circular magnetic field lines around straight conductors carrying current.
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So, it's better to use $\mu_0 \mu_r$ for accuracy. Thanks...