what is the energy now stored if the capacitor was disconnected from the potential source before the separation of the plates was changed

Final energy = Uf = initial energy × d₂/d₁

Explanation:

Energy is the ability to do work.

capacitor is an electronic device that store charges

where

V is the potential difference

d is the distance of seperation between the two plates

ε₀ is the dielectric constant of the material used in seperating the two plates, e.g., paper, mica, glass etc.

A = cross sectional area

U =¹/₂CV²

C =ε₀A/d

C × d=ε₀A=constant

C₂d₂=C₁d₁

C₂=C₁d₁/d₂

charge will  'q' remains same in the capacitor, if the capacitor was disconnected from the electric potential source (v) before the separation of the plates was replaced

Energy=U =(1/2)q²/C

U₂C₂ = U₁C₁

U₂ =U₁C₁ /C₂

U₂ =U₁d₂/d₁

Final energy = Uf = initial energy × d₂/d₁