Electrostatic Potential and CapacitanceNEET Physics · Class 12 · NCERT Chapter 2

You can expect 1 to 2 questions from this chapter in NEET 2027. The chapter has very high PYQ frequency. Potential of a point charge, capacitor combinations (series and parallel), parallel plate capacitor with dielectric, and energy stored are the most repeated topics.

Electric potential V at a point is the work done by an external agent in moving a unit positive charge from infinity to that point against the electric field. SI unit is volt (V), where 1 V equals 1 J per C. For a point charge q at distance r, V equals k q over r. Potential is a scalar; you simply add (with sign) for many charges.

E equals minus dV over dr. The field points from high potential to low potential. The negative gradient of V gives the field. If V is constant in some region, E equals 0 there. Equipotential surfaces are always perpendicular to field lines.

A capacitor is a device that stores electric charge and energy. It is made of two conductors separated by an insulator. When connected to a battery, charge plus Q gathers on one plate, minus Q on the other. Capacitance C is defined as Q over V, where V is the potential difference across the plates. SI unit is farad (F).

For two flat plates of area A separated by distance d in vacuum, C equals epsilon_0 A over d. The capacitance increases with bigger plates and decreases with larger separation. Inserting a dielectric of dielectric constant K makes C equals K epsilon_0 A over d.

Parallel: each capacitor has the same V, so their charges add. C_eff equals C_1 plus C_2 plus C_3. Series: each carries the same charge Q, so their voltages add. 1 over C_eff equals 1 over C_1 plus 1 over C_2 plus 1 over C_3. Series gives a smaller effective C; parallel gives a larger one.

U equals half Q V equals half C V squared equals half Q squared over C. The energy lives in the electric field between the plates. Energy density (energy per unit volume in vacuum) is u equals half epsilon_0 E squared.