what is energy density of an electric field (in capicators ) ?

Hi,

Energy density is the amount of energy stored per unit volume of given system.

As we know energy stored in the capacitor is,

And as E=σ/є₀ (for parallel plate capacitor), σ=Q/A, C=Q/V and V=Ed

Then volume = Ad

Energy stored = ½є₀AdE²

Energy density = Energy stored/volume = ½є₀ E²

Hope, this answer helps.

Cheers!