Toroidal moment

<p>In <a href="/facts/Electromagnetism/oAkmALHT">electromagnetism</a>, a toroidal moment is an independent term in the <a href="/facts/Multipole_expansion/Kao2WRBA">multipole expansion</a> of the <a href="/facts/Electromagnetic_field/MacraS8y">electromagnetic field</a> which is distinct from magnetic and electric <a href="/facts/Multipole/Kao2WRBA">multipoles</a>. In the <a href="/facts/Electrostatic/bxkuW6s4">electrostatic</a> multipole expansion, all <a href="/facts/Charge_density/xFDPXUDM">charge</a> and <a href="/facts/Current_density/IlUKSe2B">current distributions</a> can be expanded into a complete set of electric and magnetic multipole coefficients. However, additional terms arise in an electrodynamic multipole expansion. The coefficients of these terms are given by the toroidal multipole moments as well as <a href="/facts/Time_derivative/AWV28T13">time derivatives</a> of the electric and magnetic multipole moments. While <a href="/facts/Electric_dipole/ou2LDUVg">electric dipoles</a> can be understood as separated charges and <a href="/facts/Magnetic_dipole/Ny0TVUSX">magnetic dipoles</a> as circular currents, axial (or electric) toroidal dipoles describe <a href="/facts/Toroid/EzsnyLtR">toroidal</a> (donut-shaped) charge arrangements whereas a polar (or magnetic) toroidal dipole (also called an anapole) corresponds to the field of a <a href="/facts/Solenoid/4aQLSkjp">solenoid</a> bent into a <a href="/facts/Torus/J9SkaV1W">torus</a>.
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Toroidal moment open-in-new

Toroidal moment