Dielectric strength
= Dielectric strength
{title2=$E_{\rm bd}$}
{wiki}
<Dielectric strength> characterizes the <electric field> at <dielectric breakdown> under specified test conditions. In an ideal uniform gap, it sets a voltage scale $V_{\rm bd}\simeq E_{\rm bd}d$.<University Physics Volume 2 by Samuel J. Ling and others/8.5 Molecular Model of a Dielectric>[§8.5: dielectric strength definition and voltage limit for a specified plate separation]{ref} The <parallel-plate capacitor> model consequently gives the stored <energy density> scale
$$
u_{\rm bd}\simeq\frac12\epsilon E_{\rm bd}^2.
$$
This is a model scale, not an operating rating: <fringing field of a capacitor> make local <electric fields> differ from $V/d$, while leakage and <dielectric loss> spend some supplied <energy> as heat. Comparing usable <capacitor energy> therefore requires insulation and breakdown performance as well as <permittivity>.