Coulomb’s law gives the electric force acting between two point charges. A point charge is a pointlike object with a nonzero electric charge. Coulomb’s law says that the force between two charges having magnitudes q1 and q2 separated by a distance r is F = ( k q1 q2) / r2 where k is a constant equal to about 8.99 × 109 N⋅m2/C2. The direction of the force on each charge is toward the other one if the charges have opposite signs (opposite charges attract each other). And the direction of the force on each charge is away from each other if the signs of the charges are the same (like charges repel each other).
With SI units, the charges are in coulombs (C) and the distance in meters (m), so the force comes out in newtons (N).
The force in Coulomb’s Law Equation (equation 1 above) is called the electric force, or the Coulomb force. This is also known as electrostatic force (“static” because the force is present whether or not the charges are moving).
Equation of Coulomb’s Law | Formula
Electrostatic force = F = ( k q1 q2) / r2 ………. (1) where k is a constant equal to about 8.99 × 109 N⋅m2/C2. This force acts between two charges having magnitudes q1 and q2 separated by a distance r.
Direction of Electric Force
The direction of the electric force exerted on one point charge due to another point charge is always along the line that joins the two point charges.
Remember that, unlike the gravitational force, the electric force can either be attractive or repulsive, depending on the signs of the charges.
The direction of the force on each charge is toward the other one if the charges have opposite signs (opposite charges attract each other). And the direction of the force on each charge is away from each other if the signs of the charges are the same (like charges repel each other).
The similarity between electric force formula and gravity formula
There are some similarities between the electric force formula and the gravity formula. These are as follows:
1] Like gravity, the electric force is an inverse square law force. such that The force is proportional to the inverse square of the separation r between the two point charges (F ∝ 1/r^2). That means the strength of the force decreases as the separation increases.
2] The strength of the force is also proportional to the magnitude of each of the two charges (∣q1∣ and ∣q2∣) just as the gravitational force is proportional to the mass of each of two interacting objects.
Sample Numerical problem solved using Coulomb’s Law
1 ] What is the force of attraction between the electron and proton in a hydrogen atom?
The negative sign here refers that it’s a force of attraction between electron and proton.
Summary | Take away | Suggested Reading
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Anupam M is a Graduate Engineer (Electronics & Communication Engineering, National Institute of Technology -NIT Graduate) who has 2 decades of hardcore experience in Information Technology and Engineering. He is an avid Blogger who writes a couple of blogs of different niches. He loves to teach High School Physics and utilizes his knowledge to write informative blog posts on related topics. Anupam M is the founder and author of PhysicsTeacher.in Blog.