A capacitor is a system of two conductors separated by an insulating medium. Capacitance of this system is determined purely geometrically, by the shapes, size and relative position of the conductors. The medium between the two conductors can be air or a dielectric. The way the dielectric is inserted accordingly by capacitance changes. Electric energy is stored in the capacitors. The capacitor can be connected in series or in parallel in an electric circuit.
The plates of a parallel plate capacitor with area of each plate \( A \) and charge \( Q \) attract each other with a force.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( \displaystyle\frac{Q^2}{2A\varepsilon_0} \)
A plate is pulled only by the field of the other plate; a charged plate exerts no net force on itself. The field of one large plate with surface charge density \( \sigma = Q/A \) is
\( \displaystyle E_{\mathrm{one}} = \frac{\sigma}{2\varepsilon_0} = \frac{Q}{2A\varepsilon_0} \)
The force on the charge \( Q \) of the other plate is
\( \displaystyle F = Q\,E_{\mathrm{one}} = \frac{Q^2}{2A\varepsilon_0} \)