What is the Electrostatic Force?
The word Electo in electrostatic is for electric charges and static means at rest. So, the study of force between two like or alike charges is called electrostatic force.
Any stable atom always contains the electrostatic force of attraction. An electrostatic force is also known as the Coulombic force. It is the force of attraction between two opposing charges, i.e., protons and electrons. Here, the strong electrostatic force of attraction between them stabilizes the atomic particle.
On this page, we will define electrostatic force and discuss the real-life applications of electrostatic force in detail.
Define Electrostatic Force
An electrostatic force or the Coulombic force is defined as the force of attraction or repulsion between two like and unlike charges, respectively. The two charges bear equal magnitude but opposite charges and are separated by some distance.
An imaginary line exists between these two charges to mark their distance from each other. Also, the charges have the square of the distance between them.
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Now, we will learn to find the electrostatic force between the two charges, viz: q1 & q2 in the following context:
Electrostatic Force
Take a balloon and a piece of wool. Now, rub the balloon with this piece of wool, a heat generated on the balloon’s surface.
Bring a few pieces of paper near to this balloon, you see that pieces of paper get attracted to the balloon. It is because an electrostatic force of attraction builds between the balloon and the pieces of paper.
Coulomb’s Law
We can quantify the electrostatic force between two charged particles by using Coulomb’s law. Coulomb’s law usually applies to point charges and gives a relationship between the electrostatic force, the magnitude of the charges, and the distance between them. According to this law, the force between the two particles is stated in the following manner:
Electrostatic force varies proportionally with the product of the magnitude of the charges
Varies inversely with the square of the distance between the two equal and opposite charges.
Coulombic Force
A Coulombic force can be explained by the following equation:
\[F \alpha \frac{q_{1}q_{2}}{r^{2}}\]
Here,
q1 = a positive/negative charge or vice versa
q2 = a negative/positive charge or vice versa
r² = the distance between the two charges (both of equal and opposite magnitude)
Now, removing the sign of the proportionality constant, we rewrite the equation as;
\[F=K \frac{q_{1}q_{2}}{r^{2}}\]
Here, k is the constant and it is known as the electrostatic constant or the force constant.
Define Coulomb Constant
The Coulomb constant was named after the French physicist named Charles-Augustin de Coulomb who introduced Coulomb's law.
The value of ‘k’ is approximately equal to 8.987 5517923 (14) x 109 kg.m3.s-2.C-2
According to the above equation (2), F disappears when r approaches infinity. Thus, at infinity or a large distance, the electrostatic force reaches zero. Scientifically, the range of F is infinite.
The work done W by the force F on a particle is the product of the force and the displacement d. The equation is as follows:
W= F x d
The work done in moving the charged particle from one position to another is independent of the path taken. Hence, the electrostatic force is conservative in nature.
Examples of Electrostatic Force
The rubbing of clouds produces electrostatic charges. These charges get neutralized by passing through the atmosphere until they reach the neutral ground. We perceive this phenomenon as lightning.
After combing your hair, if you bring the wet comb close to a piece of paper, an electrostatic force of attraction between the comb and trace of the paper develops, and the paper sticks with the comb.
A silk shirt sticks to the body because of charged particles on the shirt. The same phenomenon applies to a woollen pullover when taking off.
Getting out of a vehicle on a warm, dry day and touching its door gives us charges.
Grains of sugar get attracted to the inside surface of a container due to electrostatic forces.
The surface of the truck carries a lot many charges and when any vehicle passes the truck, the electrostatic force generates between the charged particles on the truck’s surface and the charges present in the air.
Point to Note:
Electrostatic forces are present at places where charged particles interact through a polar medium. Hence, electrostatic forces are particularly crucial for ceramic materials in polar media viz: water and ethanol. The electrostatic forces are usually stronger and have a longer range than all other surface forces.
Applications of Electrostatic Force
The electrostatic force carries multiple real-life applications, and a few of these are discussed below:
Photocopying machines
Laser and ink-jet printers
Van der Graaff generator
Smoke precipitator, and
CCD (charged-couple device) camera
FAQs on Coulombic Force
1. What is Coulombic force, as defined by Coulomb's Law for the CBSE 2025-26 syllabus?
The Coulombic force, also known as electrostatic force, is the force of attraction or repulsion between two stationary point charges. According to Coulomb's Law, this force is directly proportional to the product of the magnitudes of the two charges and inversely proportional to the square of the distance between their centres. It acts along the straight line connecting the two charges.
2. How do you calculate the Coulombic force between two point charges?
To calculate the Coulombic force (F), you use the formula derived from Coulomb's Law: F = k * |q1*q2| / r². In this formula:
- F is the magnitude of the electrostatic force.
- k is the Coulomb constant, approximately 8.99 × 10⁹ N·m²/C².
- q1 and q2 are the magnitudes of the two point charges.
- r is the distance between the charges.
The direction of the force is attractive if the charges have opposite signs and repulsive if they have the same sign.
3. What are the key differences and similarities between Coulombic force and Gravitational force?
While both forces follow an inverse-square law, there are crucial distinctions:
- Nature of Force: Gravitational force is always attractive, whereas Coulombic force can be either attractive (between opposite charges) or repulsive (between like charges).
- Strength: The Coulombic force is significantly stronger than the gravitational force. For instance, the electrostatic force between an electron and a proton is about 10³⁹ times stronger than the gravitational force between them.
- Dependence on Medium: Gravitational force is independent of the medium between masses. In contrast, Coulombic force depends on the medium (characterised by its permittivity).
Their main similarity is that both are central forces that act along the line joining the interacting particles and obey the inverse-square law.
4. How does the medium between two charges, such as water or air, affect the Coulombic force?
The medium significantly affects the Coulombic force by reducing its magnitude. This effect is described by the permittivity (ε) of the medium. The force in a medium is given by F' = F / K, where F is the force in a vacuum and K is the dielectric constant of the medium. For example, water has a high dielectric constant (around 80), so it reduces the Coulombic force between two charges to about 1/80th of its value in a vacuum. This is why ionic compounds like salt dissolve in water.
5. What is the principle of superposition in the context of electrostatic forces?
The principle of superposition states that for a system of multiple point charges, the total Coulombic force on any given charge is the vector sum of the individual forces exerted on it by all other charges. Importantly, the force between any two charges is completely unaffected by the presence of other charges. This principle is fundamental for calculating the net force in complex charge distributions as per the NCERT syllabus.
6. What are some practical, real-world examples of Coulombic force in action?
Coulombic force is fundamental to many everyday phenomena:
- Static Cling: Clothes sticking together after being in a dryer is due to the electrostatic attraction between oppositely charged areas on the fabric.
- Photocopiers and Laser Printers: These devices use electrostatic forces to attract fine powder (toner) to specific areas on a charged drum, which is then transferred to paper to create an image.
- Vehicle Safety: Trucks carrying flammable materials often drag a metal chain on the ground. This provides a path for static charge, built up from air friction, to safely discharge to the Earth, preventing a spark that could ignite the fuel.
7. What are the main limitations of using Coulomb's Law?
While powerful, Coulomb's Law has specific limitations:
- It is strictly applicable only for stationary point charges. It does not hold true for charges in motion, as moving charges constitute currents and produce magnetic fields.
- It is difficult to apply for charges distributed over irregularly shaped bodies. For such cases, more advanced methods like Gauss's Law are used.
- The law assumes the charges are in a vacuum. When a medium is present, the formula must be modified using the medium's permittivity.
8. How is Coulombic force responsible for the structure and stability of an atom?
The Coulombic force is the primary force governing atomic structure. The strong electrostatic attraction between the positively charged nucleus (containing protons) and the negatively charged electrons holds the electrons in orbit around the nucleus. This force of attraction counteracts the electrons' kinetic energy, preventing them from flying away and thus ensuring the stability of the atom. It is the fundamental force that binds matter together at the atomic level.
