= Electric and magnetic pressure cancellation in a matched TEM line
{title2=$f_E=\varepsilon aV_{\rm rms}^2/(2d^2)=\mu_0I_{\rm rms}^2/(2a)=f_B$}
In a matched lossless <parallel-plate transmission line>, a single travelling wave obeys $V/I=Z_0=(d/a)\sqrt{\mu_0/\varepsilon}$. The electric attraction per unit length is $f_E=\varepsilon aV_{\rm rms}^2/(2d^2)$; each plate feels the field of the other plate, excluding its self-field. Opposite sheet currents give magnetic repulsion $f_B=\mu_0I_{\rm rms}^2/(2a)$. Substituting the travelling-wave impedance proves their equality, so the ideal net transverse electromagnetic force is zero at every phase. A standing wave or independent voltage and current need not have this cancellation.
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