Consider a simple parallel-plate capacitor whose plates are
given equal and opposite charges and are separated by a
distance d. Suppose the plates are pulled apart until they are
separated by a distance D > d. The electrostatic energy
stored in the capacitor is
1. greater than
2. the same as
3. smaller than

and what is also the ans before the plates were pulled apart

The correct answer is 3

Explanation:

The capacitance in a capacitor is

           C = ε₀ A / d

When we separate the capacitors the capacitance decreases

Let's look for capacitance

       C₀ = ε₀  A / d

       C = ε₀  A / D

The relationship between the two capacitances is

        C / C₀ = d /D

The energy stored in a capacitor is

            U = ½ C ΔV²

If we maintain the same potential difference, the stored energy decreases if the capacitance decreases

The correct answer is 3

The relationship between the two energies is

         U₀ = ½ ε₀  A / d ΔV²

         U = ½ eo A / D ΔV²

         U / U₀ = d/D