= Force on a current sheet from the mean magnetic field
{title2=$\mathbf f_S=\mathbf K\times(\mathbf B_++\mathbf B_-)/2$}
The <Lorentz force> per unit area on an ideal <current sheet> is computed using the mean of its limiting <magnetic fields>. The sheet's own local <magnetic field> is equal and opposite on its two sides and cancels in this mean. Equivalently, integrate the <Lorentz force density> through a thin regularized layer: its self-field contribution averages to zero, leaving the external field acting on the <surface current density>.
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