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   "source": [
    "# Field Inside an Air-Core Toroid Coil"
   ]
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   "metadata": {},
   "source": [
    "*This simple formula can be derived directly from [Maxwell's fourth equation](../basics/maxwell.html), or Ampere's Law.*"
   ]
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   "metadata": {},
   "source": [
    "![Infinite straight wire](toroid.png)"
   ]
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   "source": [
    "$B = \\frac {\\mu_o i N}{2\\pi r}$\n",
    "\n",
    "**B** is the magnetic field, in teslas. The direction of the field is tangent to a circle on a radius **r** (in meters) from the center of the toroid.\n",
    "\n",
    "$\\mathbf \\mu_o$ is the permeability constant (1.26x10<sup>-6</sup> Hm<sup>-1</sup>)\n",
    "\n",
    "**i** is the current in the wire, in amperes.\n",
    "\n",
    "**N** is the total number of turns of wire in the toroid."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "---\n",
    "\n",
    "[Magnet Formulas](../index.html), © 2018 by Eric Dennison. Source code and License on [Github](https://github.com/tiggerntatie/emagnet-py)"
   ]
  }
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