# Permeability of free space

The **permeability of free space**, **μ _{0}**, is a physical constant used often in electromagnetism. It is defined to have the exact value of 4π x 10

^{-7}N/A

^{2}(newtons per ampere squared).

^{[1]}It is connected to the energy stored in a magnetic field, see Hyperphysics for specific equations.

It is related to the speed of light by the equation:

where

- speed of light and is the
- permittivity of free space. is the

A magnetic field, energy density is defined as:^{[2]}

One particular use is the magnetic force. The constant gives how strong the force is between two electric currents separated by a distance:^{[1]}

where

- is the Magnetic force,
- and are two currents, and
- wires carrying the currents. is the separation between the

Visit Hyperphysics for more information on this constant.

## For Further Reading

For further information please see the related pages below:

## References

- ↑
^{1.0}^{1.1}Hyperphysics. (August 28, 2015).*Electric field*[Online], Available: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elefie.html - ↑ Jackson, John David (1998). Classical Electrodynamics (3rd ed.). New York: Wiley. p. 213