Ch 2Electrostatic Potential and Capacitance — Class 12 Physics, concept-first.

In earlier chapters, you learned that conservative forces (like gravity and spring force) store work as potential energy.

When we place a test charge in an electric field , the electrostatic force on it is . The work done to move this charge is proportional to .

The electric potential at a point due to a point charge is the work done per unit positive test charge in bringing it from infinity to that point, against the electrostatic force.

An electric dipole consists of two equal and opposite charges and separated by a small distance . Its total charge is zero, but it has a dipole moment vector with magnitude , pointing from to .

The electric potential at a point due to a collection of point charges is simply the algebraic sum of the potentials due to each individual charge.

An equipotential surface is a surface over which the electric potential is constant at every point. This means that the potential difference between any two points on the same equipotential surface is…

The electric field and potential are not independent — they describe the same electrostatic situation from different angles.

Electrostatic force is conservative. This means the work done to assemble a group of charges from infinity does not depend on the path taken.

When a charge is placed in an external electric field, it experiences a force. To bring the charge from infinity (where the field is zero) to a specific point in the field, work must be done against t…

The potential energy of a single charge in an external field is different from the potential energy of a system of charges (Section 2.7).

When a system of charges is placed in an external electric field, the total potential energy has two parts:

When an electric dipole (charges and separated by distance ) is placed in a uniform external electric field , it experiences no net force but a torque .

Conductors (like metals) have free electrons that can move throughout the material. In a static situation (no current), these charges rearrange themselves until they reach equilibrium.

- Conductors have free charge carriers. In an external field, these carriers move until the induced field exactly cancels the external field inside the conductor — net field is zero.

A capacitor is a system of two conductors separated by an insulator (dielectric). In the most common configuration, the two conductors carry equal and opposite charges: and .

A parallel plate capacitor is the simplest and most common type of capacitor. It consists of two large, plane, parallel conducting plates separated by a small distance.

When a dielectric material is placed between the plates of a capacitor, the capacitance increases. This happens because the dielectric reduces the effective electric field between the plates for the s…

Capacitors are often connected together in circuits to achieve a specific total (or effective) capacitance that is not available from a single capacitor.

When capacitors are connected in series, the key physical constraint is that the charge on each capacitor is identical.

When capacitors are connected in parallel, the potential difference across each capacitor is the same (equal to the supply voltage ).

A capacitor stores electrostatic potential energy. This energy is the work done to assemble the charges on its plates against the repulsive forces that build up as the capacitor charges.

- Electrostatic Potential is the work done per unit charge to bring a test charge from infinity to a point in an electric field: . It is a scalar quantity.

1. Electrostatics studies forces between stationary charges. However, if a net Coulomb force acts on a charge, it would accelerate.

Higher-order thinking / exemplar-style practice problems.

Sample papers and previous-year board questions for this subject.