Coulombs-Law

Coulomb’s Law

What is Coulomb’s Law about?

Coulomb’s law (likewise called Coulomb’s inverse-square law) is a law of physics that specifies the amount of force in between two stationary, electrically charged particles (known as the electrostatic force). Coulomb’s law was discovered by Charles-Augustin de Coulomb in 1785. Hence the law and the associated formula were called after him.

Statement of Coulomb’s Law

According to Coulomb’s law, the force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance in between them. It acts along the line joining up with the two charges thought about to be point charges.

Coulomb’s Law Mathematical Form

Let us suppose, Q1 and Q2 are the electrical charges of two objects. The distance between the charges is ‘r’, and the force of attraction or repulsion in between them is ‘F’. Then

F q1q2

Or, F1/r2

F = k q1q2/ r2

Mathematical-Form

where k is proportionality constant and equals 1/4 π ε. Here, ε is the epsilon naught and it represents the permittivity of a vacuum. The value of k comes 9 × 109 Nm2/ C2 when we take the S.I unit of value of ε is 8.854 × 10-12 C2 N-1 m-2.

According to this theory, like charges repel each other and unlike charges attract each other. This suggests charges of the same sign will push each other with repulsive forces while charges with opposite signs will pull each other with attractive force.

Coulomb’s law equation gives a precise description of the force between two objects whenever the things act as point charges. A charged performing sphere connects with other charged things as though all of its charges lay at its center. While the charge is uniformly spread out throughout the surface of the sphere, the center of charge can be considered to be the center of the sphere.

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The sphere acts as a point charge with its excess charge found at its center. Because Coulomb’s law applies to point charges, the distance r in the formula is the distance between the centers of charge for both objects (not the distance in between their closest surfaces).

Application of Coulomb’s Law
  • To determine the distance and force between the two charges.
  • To determine the force on one point due to the presence of several points.
Limitations of the Law

The law applies just for the point charges at rest.

  • Coulomb’s Law can be just applied in those cases where the inverse square law is complied with.
  • It is challenging to execute Coulomb’s law where charges remain in approximate shape since in such cases, we can not identify the distance in between the charges.
  • The law can’t be utilized directly to determine the charge on the big planets or objects.

MCQs:

  • 1. What is Coulomb’s Law primarily concerned with?
    • A) Gravitational forces between celestial bodies
    • B) Magnetic interactions between particles
    • C) Electrically charged particles at rest
    • D) Kinetic energy of moving charges
    • Answer: C) Electrically charged particles at rest
  • 2. Who is credited with discovering Coulomb’s Law?
    • A) Albert Einstein
    • B) Isaac Newton
    • C) Charles-Augustin de Coulomb
    • D) Michael Faraday
    • Answer: C) Charles-Augustin de Coulomb
  • 3. Which of the following statements best describes Coulomb’s Law?
    • A) The force of attraction between two magnetic poles is inversely proportional to the distance between them.
    • B) The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
    • C) The force experienced by a moving charge in a magnetic field is proportional to the velocity of the charge.
    • D) The force between two charges is directly proportional to the square of the distance between them.
    • Answer: B) The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
  • 4. What does ‘r’ represent in the mathematical formulation of Coulomb’s Law?
    • A) Speed of light
    • B) Permittivity of vacuum
    • C) Distance between charges
    • D) Charge of the particles
    • Answer: C) Distance between charges
  • 5. Which statement correctly describes the behavior of charges according to Coulomb’s Law?
    • A) Charges of the same sign attract each other.
    • B) Charges of opposite signs repel each other.
    • C) Charges of the same sign repel each other.
    • D) Charges of opposite signs neither attract nor repel.
    • Answer: C) Charges of the same sign repel each other.
  • 7. Coulomb’s Law applies to:
    • A) Moving charges only
    • B) Point charges at rest only
    • C) Moving and stationary charges
    • D) Charged particles in motion with constant velocity
    • Answer: B) Point charges at rest only
  • 8. In what scenario can Coulomb’s Law not be directly applied?
    • A) When dealing with stationary charges
    • B) When the inverse square law is not followed
    • C) When the charges are in motion
    • D) When dealing with charged spheres
    • Answer: B) When the inverse square law is not followed
  • 9. What is the primary limitation of Coulomb’s Law?
    • A) It does not account for the motion of charges.
    • B) It only applies to non-metallic materials.
    • C) It is not applicable to charges in motion.
    • D) It only applies to point charges at rest.
    • Answer: D) It only applies to point charges at rest.
  • 10. Coulomb’s Law can be utilized to determine:
    • A) The energy stored in a capacitor
    • B) The magnetic flux through a solenoid
    • C) The force between two charges
    • D) The induced current in a conductor
    • Answer: C) The force between two charges
  • 11. The force between two charges according to Coulomb’s Law is stronger when:
    • A) The charges have opposite signs
    • B) The charges have the same sign
    • C) The distance between the charges increases
    • D) The charges are metallic
    • Answer: A) The charges have opposite signs
  • 12. What is the S.I. unit of the proportionality constant ‘k’ in Coulomb’s Law?
    • A) N/C
    • B) C
    • C) Nm²/C²
    • D) Nm/C
    • Answer: C) Nm²/C²
  • 13. Coulomb’s Law primarily deals with:
    • A) Gravitational interactions
    • B) Magnetic interactions
    • C) Electrostatic interactions
    • D) Nuclear interactions
    • Answer: C) Electrostatic interactions
  • 14. The force between two charges is maximum when:
    • A) The charges are of the same sign and far apart
    • B) The charges are of opposite signs and close together
    • C) The charges are of opposite signs and far apart
    • D) The charges are of the same sign and close together
    • Answer: B) The charges are of opposite signs and close together
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Summary:

Coulomb’s Law, also known as Coulomb’s inverse-square law, governs the force between stationary, electrically charged particles. Discovered by Charles-Augustin de Coulomb in 1785, the law states that the force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Mathematically, this is represented as , where is the proportionality constant. Like charges repel each other, while unlike charges attract. Coulomb’s law applies to point charges, treating charged objects as though all of their charges were concentrated at their centers.

It finds applications in determining the distance and force between charges and understanding the force on a point due to the presence of multiple charges. However, the law has limitations—it applies only to point charges at rest and requires compliance with the inverse square law.

Additionally, it is challenging to apply when charges are not point-like or when determining charges on large objects like planets.

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