3D plot of the absolute value of the <a href="https://en.wikipedia.org/wiki/magnetic_field" class="extiw" title="w:magnetic field">magnetic field</a> <i>B</i> of a <a href="https://en.wikipedia.org/wiki/Maxwell_coil" class="extiw" title="w:Maxwell coil">Maxwell coil</a> consisting of three thin circular coils arranged to create a maximally uniform field in the center. The inner central coil has radius <i>R</i> and current <i>I</i>. The two outer coils have radii <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\sqrt {4/7}}R}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mrow class="MJX-TeXAtom-ORD"><msqrt><mn>4</mn><mrow class="MJX-TeXAtom-ORD"><mo>/</mo></mrow><mn>7</mn></msqrt></mrow><mi>R</mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle {\sqrt {4/7}}R}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2ed5e9a18c10ee9ba75c91948d494acc7955f598" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -1.838ex; width:7.575ex; height:4.843ex;" alt="{\displaystyle {\sqrt {4/7}}R}"></span>, axial distance <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\sqrt {3/7}}R}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mrow class="MJX-TeXAtom-ORD"><msqrt><mn>3</mn><mrow class="MJX-TeXAtom-ORD"><mo>/</mo></mrow><mn>7</mn></msqrt></mrow><mi>R</mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle {\sqrt {3/7}}R}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a27fb02eb561bf94c7ce155362f54c68475d0848" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -1.838ex; width:7.575ex; height:4.843ex;" alt="{\displaystyle {\sqrt {3/7}}R}"></span> and carry the current 49/64<i>I</i>. The central coil radius <i>R</i> is set to 1. The <i>B</i>-field is given in units of the central field <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle 15/16I\mu _{0}/R}"><semantics><mrow class="MJX-TeXAtom-ORD"><mstyle displaystyle="true" scriptlevel="0"><mn>15</mn><mrow class="MJX-TeXAtom-ORD"><mo>/</mo></mrow><mn>16</mn><mi>I</mi><msub><mi>μ<!-- μ --></mi><mrow class="MJX-TeXAtom-ORD"><mn>0</mn></mrow></msub><mrow class="MJX-TeXAtom-ORD"><mo>/</mo></mrow><mi>R</mi></mstyle></mrow><annotation encoding="application/x-tex">{\displaystyle 15/16I\mu _{0}/R}</annotation></semantics></math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9363593f322de109c89e6a8c9efcb6130ea05678" class="mwe-math-fallback-image-inline" aria-hidden="true" style="vertical-align: -0.838ex; width:12.366ex; height:2.843ex;" alt="{\displaystyle 15/16I\mu _{0}/R}"></span>.
<a href="//commons.wikimedia.org/wiki/User:Geek3" title="User:Geek3">Geek3</a>
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This  diagram was created with <a href="https://en.wikipedia.org/wiki/Mathematica" class="extiw" title="w:Mathematica">Mathematica</a>.