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Electrostatics - Coulomb's Law of Electrostatic

Electrostatics - Coulomb's Law of Electrostatic

Edited By Team Careers360 | Updated on Jul 02, 2025 04:59 PM IST

Have you ever tried to stick a balloon to a wall after rubbing it on your hair? So you might be curious about what Force is acting between the wall and the balloon. This powerful force is Electrostatic Force. By rubbing the balloon on your hair, you’re transferring tiny electric charges to it, making it attract to the wall, almost like a magnet. From printers to radar, everything involves Electrostatic force. In this article, we will explore the concept of Electrostatic force in detail.

This Story also Contains
  1. What is Electrostatic Force?
  2. Applications of Electrostatic Forces
  3. Coulomb's law of electrostatic:
  4. Properties of Electrostatic Force
Electrostatics - Coulomb's Law of Electrostatic
Electrostatics - Coulomb's Law of Electrostatic

What is Electrostatic Force?

The force acting between two stationary charged particles is called an Electrostatic force. These charged particles can either pull the object toward each other (if the charges are opposite) or push the object away (if the charges are similar).

S.I. Unit of Electrostatic Force

The S.I. unit of electrostatic force is the Newton (N).

Applications of Electrostatic Forces

Some of the uses of Electrostatic force are as follows:
1. In electrostatic loudspeaker.
2. In electrostatic sprinkling of paints and powder coating.
3. In flyash collection in chimneys.
4. In a Xerox copying machine.
5. In the designing of a cathode-ray tube that is used in television and radar.

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Coulomb's law of electrostatic:


Coulomb's law states that the attractive or repulsive forces amongst two fixed-point charges are:

  • Directly proportional to the product of the magnitudes of the charges, and
  • Inversely proportional to the square of the distance between them. This force acts along the line relating the two charges.
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Coulomb's law

$$
F=\frac{k \cdot\left|q_1 \cdot q_2\right|}{r^2}
$$

where:

  • $F=$ Electrostatic force between the charges (in Newtons, N)
  • $k=$ Coulomb's constant $\left(8.9875 \times 10^9 \mathrm{~N} \mathrm{~m}^2 / \mathrm{C}^2\right)$
  • $q_1$ and $q_2=$ Magnitudes of the two charges (in Coulombs, C)
  • $r=$ Distance between the centers of the two charges (in meters, m )

It is a law that governs electrostatic force.

Properties of Electrostatic Force

Attractive or Repulsive: Electrostatic Force can be either repulsive or Attractive in nature, depending on the charges involved.

  • If the charges are similar (both positive or both negative) then repulsion will take place.
  • If the charges are opposite (one positive and one negative) then attraction will take place.

Distance Dependent: Electrostatic force is inversely proportional to the distance between the charges as per the Coloumb's law. This means that force decreases as the distance between the charges increases.

Obeys Newton's Third Law: Electrostatic forces between two charges are equal in magnitude and opposite in direction. If one charge exerts a force on another, the second charge exerts an equal and opposite force on the first.

Conservative Force: It means that work done to move a charge from one point to another will depend only on the final and initial position, and remain independent on the path taken. This can be understood by learning the concept of Conservative and Non-conservative forces.

Magnitude Proportional to Charge: The electrostatic force is directly proportional to the product of the magnitudes of the charges involved. Larger charges result in a stronger force.

Frequently Asked Questions (FAQs)

1. What is meant by electrostatic?

Electrostatic is a branch of physics which works with the static electric charges.

2. Write two applications of electrostatics.

In making loudspeaker and in sprinkling of paints and powder coating.

3. What is the unit of electrostatic force constant?

Unit of electrostatic force constant = N  m2 C-2

4. What is the law of electrostatic?

Alike charges repels and unlike charges attracts each other.

5. Which physicist gave coulomb’s law?

Charles Augustin Coulomb

6. How does Coulomb's Law explain the concept of electrostatic shielding?
Electrostatic shielding is based on the fact that electric fields and forces cannot penetrate a conductor in electrostatic equilibrium. Inside a hollow conductor, the net electric field is zero due to the arrangement of charges on the conductor's surface. This arrangement is a consequence of Coulomb's Law and the tendency of like charges to repel each other.
7. Can Coulomb's Law be used to calculate the force between moving charges?
Coulomb's Law in its basic form applies to stationary charges. For moving charges, additional factors like magnetic fields come into play, and more complex electromagnetic laws are needed. However, for charges moving at speeds much lower than the speed of light, Coulomb's Law still provides a good approximation.
8. What is the superposition principle in electrostatics, and how does it relate to Coulomb's Law?
The superposition principle states that the net electrostatic force on a charge due to multiple charges is the vector sum of the individual forces exerted by each charge. This principle allows us to use Coulomb's Law to calculate the force on a charge in complex systems by summing the contributions from all other charges.
9. How does the concept of electric potential energy relate to Coulomb's Law?
Electric potential energy is the energy stored in a system of charges due to their positions relative to each other. It's calculated by integrating the force from Coulomb's Law over distance. The change in potential energy when moving a charge in an electric field is equal to the work done against the electrostatic force.
10. How does Coulomb's Law apply to the distribution of charge on a conductor?
In a conductor, free electrons can move in response to electric fields. According to Coulomb's Law, like charges repel each other. This repulsion causes excess charge on a conductor to distribute itself on the surface to minimize the repulsive force between charges. The charge distribution will be such that the electric field inside the conductor is zero in electrostatic equilibrium.
11. What is Coulomb's Law of Electrostatic Force?
Coulomb's Law states that the electrostatic force between two point charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them. It is expressed mathematically as F = k(q1q2)/r^2, where F is the force, k is Coulomb's constant, q1 and q2 are the magnitudes of the charges, and r is the distance between them.
12. What is the significance of Coulomb's constant (k) in the equation?
Coulomb's constant (k) is a proportionality constant that determines the strength of the electrostatic force. Its value is approximately 8.99 × 10^9 N⋅m^2/C^2 in vacuum. The constant relates the units of charge, distance, and force, ensuring that the equation is dimensionally consistent.
13. Why is the inverse square relationship important in Coulomb's Law?
The inverse square relationship in Coulomb's Law (1/r^2) is crucial because it describes how the electrostatic force decreases with increasing distance. This relationship explains why electrostatic forces are strong at short distances but become weaker rapidly as objects move apart, similar to gravitational forces.
14. How does Coulomb's Law differ from Newton's Law of Gravitation?
While both laws follow an inverse square relationship, Coulomb's Law deals with electric charges, while Newton's Law of Gravitation deals with masses. Electrostatic forces can be attractive or repulsive, whereas gravitational forces are always attractive. Additionally, the electrostatic force is much stronger than the gravitational force for particles of similar mass and charge.
15. Can Coulomb's Law be applied to all types of charged objects?
Coulomb's Law in its simplest form applies to point charges or spherically symmetric charge distributions. For more complex charge distributions or non-point charges, the law needs to be integrated over the charge distribution. However, the basic principle still holds for calculating the net force between charged objects.
16. Why do like charges repel and unlike charges attract?
Like charges repel and unlike charges attract due to the nature of the electric field. Positive charges create outward-pointing electric field lines, while negative charges create inward-pointing lines. When two like charges interact, their field lines push against each other, causing repulsion. For unlike charges, the field lines connect, pulling the charges together.
17. How does the medium between charges affect Coulomb's Law?
The medium between charges affects Coulomb's Law through its permittivity. In a medium other than vacuum, the force is reduced by a factor equal to the relative permittivity (ε_r) of the medium. The equation becomes F = k(q1q2)/(ε_r * r^2), where ε_r is always greater than 1 for any medium other than vacuum.
18. How does charge magnitude affect the strength of the electrostatic force?
The strength of the electrostatic force is directly proportional to the product of the charge magnitudes (q1q2). This means that if either charge is doubled, the force doubles. If both charges are doubled, the force quadruples. Larger charges result in stronger forces, while smaller charges result in weaker forces.
19. What happens to the electrostatic force when the distance between charges is doubled?
When the distance between charges is doubled, the electrostatic force decreases by a factor of 4. This is due to the inverse square relationship (1/r^2) in Coulomb's Law. If the distance increases by a factor of n, the force decreases by a factor of n^2.
20. How is Coulomb's Law related to the concept of electric field?
Coulomb's Law is fundamental to the concept of electric field. The electric field at a point is defined as the force per unit charge experienced by a test charge placed at that point. Mathematically, E = F/q, where E is the electric field, F is the force from Coulomb's Law, and q is the test charge.
21. What is the limitation of Coulomb's Law when dealing with time-varying electric fields?
Coulomb's Law assumes static charges and instantaneous action at a distance. For time-varying electric fields, where charges are accelerating or fields are changing rapidly, Coulomb's Law alone is insufficient. In such cases, we need to consider the full set of Maxwell's equations, which account for the finite speed of electromagnetic wave propagation and the interrelation of electric and magnetic fields.
22. Why doesn't Coulomb's Law account for the finite speed of electromagnetic interactions?
Coulomb's Law assumes instantaneous action at a distance, which doesn't account for the finite speed of electromagnetic interactions (the speed of light). This is because Coulomb's Law is a static approximation. For rapidly changing fields or moving charges at high speeds, relativistic effects become important, and more comprehensive electromagnetic theories (like Maxwell's equations) are needed to accurately describe the interactions.
23. Why doesn't Coulomb's Law work for describing the force between charges inside an atom?
Coulomb's Law doesn't accurately describe the force between charges inside an atom because at such small scales, quantum mechanical effects become significant. The behavior of electrons in atoms is governed by quantum mechanics, which considers factors like wave-particle duality and the uncertainty principle, which are not accounted for in classical electrostatics.
24. What is meant by the term "action at a distance" in the context of Coulomb's Law?
"Action at a distance" refers to the apparent ability of charges to exert forces on each other without any visible connection or medium. Coulomb's Law describes this effect mathematically, but it doesn't explain the mechanism. Modern physics explains this through the concept of fields: charges create electric fields that permeate space and interact with other charges.
25. Can Coulomb's Law be used to explain why lightning tends to strike pointed objects?
Yes, Coulomb's Law helps explain this phenomenon. The electric field strength near a charged conductor is proportional to the surface charge density. On a pointed object, the charge density is very high at the tip due to the small surface area. This results in a very strong electric field near the point, which can ionize the air and create a path for lightning discharge.
26. How does Coulomb's Law relate to the concept of electric flux?
Electric flux is a measure of the electric field passing through a given area. While Coulomb's Law directly describes the force between charges, it's integral to calculating electric fields. The electric field derived from Coulomb's Law is used to determine the electric flux through a surface, which is crucial in understanding Gauss's Law and electrostatic behavior.
27. How does Coulomb's Law explain the concept of electrostatic induction?
Electrostatic induction occurs when a charged object influences the distribution of charge in a nearby neutral object without touching it. Coulomb's Law explains this by describing how the electric field from the charged object exerts forces on the charges within the neutral object, causing them to redistribute. Positive charges are attracted towards a negative source charge, while negative charges are repelled, creating induced charges.
28. Why is it that we don't feel the enormous electrostatic forces between protons and electrons in everyday objects?
Although the electrostatic forces between individual protons and electrons are indeed very strong, we don't feel them in everyday objects because matter is typically electrically neutral. The positive charges of protons are balanced by the negative charges of electrons, resulting in no net force. The forces only become noticeable when there is a significant imbalance of charge, which is rare in everyday situations.
29. How does Coulomb's Law relate to the concept of electric dipoles?
An electric dipole consists of two equal and opposite charges separated by a small distance. Coulomb's Law is fundamental in understanding dipole behavior. The force on each charge of the dipole in an external electric field can be calculated using Coulomb's Law. The net torque on the dipole, which causes it to align with the field, is a result of these opposing forces acting on the separated charges.
30. Can Coulomb's Law be used to explain why rubbing certain materials together creates static electricity?
Yes, Coulomb's Law helps explain static electricity. When certain materials are rubbed together, electrons can transfer from one material to another due to their different electron affinities. This creates a charge imbalance. Coulomb's Law then describes the forces between these charged objects and other nearby objects, explaining phenomena like attraction of small pieces of paper to a charged balloon.
31. How does the concept of work in physics relate to Coulomb's Law?
Work in electrostatics is defined as the energy transferred when a charge moves in an electric field. The work done to move a charge in an electric field is equal to the change in its potential energy. This potential energy is derived from Coulomb's Law by integrating the force over distance. The work-energy theorem in electrostatics is a direct consequence of Coulomb's Law.
32. Why doesn't Coulomb's Law violate Newton's Third Law of Motion?
Coulomb's Law doesn't violate Newton's Third Law because the forces between two charges are always equal in magnitude and opposite in direction, regardless of the charges' signs or magnitudes. If charge A exerts a force on charge B, charge B exerts an equal and opposite force on charge A. This is consistent with Newton's Third Law, which states that for every action, there is an equal and opposite reaction.
33. How does Coulomb's Law explain the concept of electrostatic equilibrium?
Electrostatic equilibrium occurs when charges are distributed such that there is no net force on any charge. Coulomb's Law explains this by showing that in equilibrium, the vector sum of all electrostatic forces on each charge must be zero. In conductors, this results in all excess charge moving to the surface, and in the absence of an external field, the charges distribute to make the internal electric field zero.
34. What is the relationship between Coulomb's Law and the principle of conservation of charge?
While Coulomb's Law doesn't directly state the conservation of charge, it's consistent with and supports this principle. The law assumes that charges have fixed values and interact based on these values. The conservation of charge principle states that the total charge in an isolated system remains constant. Coulomb's Law describes the interactions between these conserved charges, never creating or destroying charge in the process.
35. How does Coulomb's Law explain why charge always flows from higher to lower potential?
Coulomb's Law underlies the concept of electric potential. The potential difference between two points is related to the work done against the electrostatic force (derived from Coulomb's Law) to move a charge between these points. Charges naturally move from high to low potential because this reduces the system's potential energy, following the principle of minimum energy. The force described by Coulomb's Law drives this movement.
36. Can Coulomb's Law be used to explain the behavior of charged particles in a uniform electric field?
Yes, Coulomb's Law is fundamental to understanding the behavior of charged particles in a uniform electric field. While the law directly describes the force between point charges, it's used to derive the concept of electric field. In a uniform field, the force on a charged particle is constant (F = qE), leading to constant acceleration. This explains phenomena like the deflection of electrons in a cathode ray tube.
37. How does Coulomb's Law relate to the concept of capacitance?
Coulomb's Law is crucial in understanding capacitance. The capacitance of an object is its ability to store electric charge. The electric field between the plates of a capacitor, which determines its capacitance, is a direct result of the charges on the plates interacting according to Coulomb's Law. The energy stored in a capacitor is ultimately derived from the work done against the Coulomb force to separate charges.
38. Why is Coulomb's Law considered a fundamental law in electrostatics?
Coulomb's Law is considered fundamental because it forms the basis for understanding all electrostatic interactions. It describes the most basic interaction between electric charges and is the starting point for deriving more complex electrostatic concepts and laws, such as electric fields, potential, and Gauss's Law. Its simplicity and wide applicability make it a cornerstone of classical electromagnetism.
39. How does Coulomb's Law explain the phenomenon of charge screening in electrolyte solutions?
Charge screening in electrolyte solutions can be explained using Coulomb's Law. In a solution, ions of opposite charge surround a central ion, forming an "ionic atmosphere." This arrangement reduces the effective electric field of the central ion at a distance, as described by Coulomb's Law. The screening effect modifies the apparent strength of electrostatic interactions, leading to phenomena like the Debye length in electrolyte solutions.
40. What is the connection between Coulomb's Law and the concept of electric field lines?
Electric field lines are a visual representation of the electric field described by Coulomb's Law. The direction of these lines indicates the direction of the force on a positive test charge, while their density represents the field strength. The shape and distribution of field lines around charges or charged objects directly reflect the inverse square nature of Coulomb's Law, showing how the field strength decreases with distance.
41. How does Coulomb's Law apply to the phenomenon of electrostatic levitation?
Electrostatic levitation occurs when the upward electrostatic force on an object balances the downward gravitational force. Coulomb's Law is used to calculate the electrostatic force between the charged object and the charged plate or electrodes providing the levitation. By adjusting the charges and distances, the electrostatic force can be made to exactly counteract gravity, achieving stable levitation.
42. Can Coulomb's Law explain why certain materials become polarized in an electric field?
Yes, Coulomb's Law helps explain polarization. In a dielectric material placed in an electric field, the electrons in each atom or molecule experience a force described by Coulomb's Law. This force causes a slight separation of positive and negative charges within the material, creating induced dipoles. The strength of this polarization depends on the field strength and the material's properties, all of which can be analyzed using Coulomb's Law.
43. How does Coulomb's Law relate to the concept of electrostatic pressure?
Electrostatic pressure arises from the repulsion between like charges on a surface. Coulomb's Law describes this repulsive force, which, when considered over an area, results in a pressure. This pressure tends to push charges apart and can cause effects like the expansion of a charged balloon or the spraying of charged liquids. The magnitude of this pressure is directly related to the surface charge density and can be calculated using Coulomb's Law.
44. How does Coulomb's Law explain the concept of image charges in electrostatics?
The method of image charges is a problem-solving technique in electrostatics based on Coulomb's Law. When a charge is placed near a conducting surface, it induces a charge distribution on the surface. This distribution can be mathematically represented by an "image charge" on the other side of the surface. The electric field and potential due to this system can then be calculated using Coulomb's Law, simplifying complex boundary problems.
45. What is the relationship between Coulomb's Law and the principle of superposition in electrostatics?
The principle of superposition in electrostatics states that the total electric field at a point due to multiple charges is the

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