Explain the concept of a parallel plate capacitor. State its any 'two' applications.
The surface of an isolated charge conductor is an equipotential surface with a potential V with respect to some arbitrary zero reference level, usually the ground. $$V > 0$$ if charge on the conductor is positive and $$V < 0$$ for negative charge. If the charge is increased. V increases in the same proportion. i.e.
$$Q \, \propto \, V$$
Removing proportionality
$$Q = CV$$
C is called the capacitance.
Consider a metal plate A whose potential is raised to V by depositing a charge $$+Q$$ on it. Now if an uncharged metal plate B is brought close to A A, then the negative charge will be induced on the surface near A and positive free change on the surface of B away from A as know below.
Ref. image.
Now if plate B is grounded, the free positive charge on B will go into the earth. The bound negative charge $$(-Q)$$ on B will lower the potential of A by say $$V_1$$ due to the presence of plate A in the electric field generated by the negative charge on B.
Now net potential on $$A = V - V_1$$
Capacity $$= \dfrac{Q}{V - V_1}$$
As $$(V - V_1)$$ has decreased from V the capacity or capacitance of plate A has increased.
This system of plates together is called a parallel plate capacitor.
Application of parallel plate capacitors:-
1) Energy storage capacitor banks are used for power factor correction with inductive loads
2) $$DC$$ power supplies sometimes use parallel capacitors in order to better filter the output signal and eliminate the $$AC$$ ripple.