#!/usr/bin/env python
# coding: utf-8

# # Field Inside a Straight, Infinite, Air-Core Solenoid

# *This simple formula can be derived directly from [Maxwell's fourth equation](../basics/maxwell.html), or Ampere's Law.*

# ![Infinite straight wire](infsolenoid.png)

# $B = \mu_o i n$
# 
# **B** is the magnetic field inside the solenoid, in teslas. The direction of the field is parallel to the axis of the solenoid. There is no field outside the solenoid.
# 
# $\mathbf \mu_o$ is the permeability constant (1.26x10<sup>-6</sup> Hm<sup>-1</sup>)
# 
# **i** is the current in the wire, in amperes.
# 
# **n** is the number of turns of wire per unit length of the solenoid, in units of $\mathrm{m^{-1}}$.

# ---
# 
# [Magnet Formulas](../index.html), © 2018 by Eric Dennison. Source code and License on [Github](https://github.com/tiggerntatie/emagnet-py)