# CBSE Class 12 Physics Chapter 2 Revision Notes

Chapter 2: Electrostatic Potential and Capacitance Revision Notes

• The amount of work done per unit positive test charge, or in bringing the unit positive test charge from infinite to that point, against the electrostatic force without acceleration, determines the electrostatic potential at any point in an electric field.

• The amount of work done in moving a unit positive test charge from one point to the other point against electrostatic force without acceleration is defined as the electrostatic potential difference between two points in an electric field.

• In addition, the potential difference between two points in an electric field is defined as the line integral of the electric field from initial position A to final position B along any path.

• A positive charge causes the potential at a point to be positive, whereas a negative charge causes it to be negative.

• When a positive charge is placed in an electric field, it is subjected to a force that propels it from higher to lower potential points. A negative charge, on the other hand, is subjected to a force that propels it from a lower to a higher potential.

• An electric dipole has no electrostatic potential on the perpendicular bisector.

• Electrostatic potential at any point P due to a system of n point charges q1, q2,…………, qn whose position vectors are r1,r2,…,rn is given by

r is the position vector of point P with respect to the origin.

• Electrostatic potential due to a thin charged spherical shell with charge q and radius R at any point P lying

• Equipotential surface refers to a surface that has the same electrostatic potential at all points on it.

• Due to line charge, the shape of the equipotential surface is cylindrical.

• Due to point charge it is spherical.

(a) Equipotential surfaces do not intersect because this would result in two directions of electric field E at the point of intersection, which is not possible.

(b) In the presence of a strong electric field, equipotential surfaces are closely spaced, and vice versa.

(c) The electric field is always normal to the equipotential surface at all points along it, and it is directed from one higher potential equipotential surface to the lower potential equipotential surface.

(d) The amount of work required to move a test charge from one point of the equipotential surface to the next is zero.

• Potential Electrostatic Energy is stored as a result of work done against electrostatic force.

ΔU = UB – UA = WAB

• In an electric field, the work required to move a unit positive test charge over a closed path is zero. As a result, electrostatic forces are conservative.

## Potential Energy of a Single Charge in an External Field

• Potential energy of a single charge q at a point with position vector r, in an external field is qV(r),

where V(r) is the potential at the point due to external electric field E.

• Potential Energy of a system of two charges in an external field

• Dipole potential energy in a uniform electric field Potential energy = -p.E

• Electrostatic Shielding is the process of creating a region that is devoid of any electric fields.

• It occurs because there is no electric field inside a charged hollow conductor. A shell’s potential is constant.

• We can also deduce that the field inside the shell (hollow conductor) will be zero in this way.

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