Electrostatics pertains to the study of stationary electric charges and their associated phenomena and properties in physics.. It primarily focuses on the behavior of these charges and their interactions at rest without considering the effects of their motion (which falls under electrodynamics). This may include the study of electric Charge, coulomb's law, electric field, electric Potential, gauss law, electrostatics potential energy, capacitors.
Charge is an inherent characteristic of matter that generates and interacts with electric and magnetic phenomena..
(1). Positive charge- Due to deficiency of electrons.
(2). Negative charge-Due to excess of electrons
(1). Additivity of electric Charge.
(2). Conservation of electric Charge
(3). Quantization of Electric Charge
(4). Charge can be transferred
(5). Charge is invariant.
(6). Charge is a scalar quantity
(7). Charge is always associated with mass
(1). Charging by Friction
(2). Charging by Induction
(3). Charging by Conduction
The electrostatic force between two point charges is proportional to the product of their magnitudes and inversely proportional to the square of the distance between them. This force acts along the line connecting the two charges at all times.
= Electrostatic constant or Coulomb’s Constant
or
When several charges interact, the total force on a given charge is the vector sum of all the individual forces exerted on it by all other charges.
Relative Permittivity or Dielectric Constant (K)
Dielectric Constant (K) =
The value of
A collection of closely positioned electric charges constitutes a continuous charge distribution.
(1). Linear Charge Density ():
(2). Surface Charge Density ():
(3). Volume Charge Density
Also Read : Electric Charges and Fields
It is a pair of two same and opposite charges placed at small separation.
(1) At Axial / End on position
(2) At Equator/Broadside on position
(3) At general position
Special Cases:
E = 0
Special cases:
Also Read : Energy Stored In a Capacitor
Note: For n point charges system
No. of pairs
It is defined as the work done by an external agent in taking a unit positive charge from a reference point to that point without changing its Kinetic Energy.
Also Read : Relation Between Electric Field and Electric Potential
Electrostatic potential due to a point charge
Expression for potential due to multiple Charges
Also Read : Electric Potential And Capacitance
Locus of all such points which are at the same potential is called equipotential surface.
Plane Charge Sheet
Q-1 Two spheres having equal charges are kept at long separation. If the gravitational force between two spheres is equal to electrostatic force between them. Find the ratio of specific charge .
Solution:
Q-2 Two thin spherical shells made of metal are at a larger distance apart . One of radius 10 cm carries a charge of +0.5 mC and the other, of radius 20 cm , carries a charge of + 0.7 mC. The charge on each, when they are connected by a suitable conducting wire is respectively.
Solution:
Q-3. The electric field in a certain region is given by . The dimensions of K are.
Solution:
Dimension of electric field = [M1L1T--3A-1]
( ∴ x representing the distance so the dimensional formula is [L]
K=[M1L1T--3A-1] [L]3
K=[M1L4T-3A-1]
Q-4. If the electric flux entering and leaving a closed surface is and respectively then electric charge inside the surface will be.
Solution:
According to Gauss Theorem,
Net Flux
Q-5. The electric potential and electric field at a point due to a point charge are 600 V and 200 N/C respectively. Calculate the magnitude of point Charge.
Solution:
Electric Potential ……..(1)
Electric Field ……..(2)
Squaring both the sides in eq.(1)
………(3)
From eq (2) and (3)
= 1800
(Session 2025 - 26)