Net Electrostatic Force: 3 Important Facts You Should Know

The net electrostatic force is the force existing when any charge or a particle goes against each other when each vector of each electric force of those respective charges is added together.

        The attractive or repulsive force between any two charged bodies due to the presence of electric charges brings the concept of electrostatic force into action.

          In classical physics, any material, when rubbed against each other, attracts particles that are lightweight, known as electrons. The force exerted by these particles is known as electrostatic and is mainly described by Coulomb’s law. In simple words, the electrostatic force is the one that exists between charges. Static is means that the charges are not moving fast.

Now that we have an idea about the electric force between these static charges let us go further in more detail about the phenomena. To start with, the electrostatic force is otherwise called as Coulomb force. This is the force exerted by one charge on another when separated by a distance.

net electrostatic force

The equation for this force is F = E/q, where E is the electric field. The total vector force is added together gives the net electrostatic force.

            For better understanding, we take few examples of daily life,

  1. While a piece of paper is rubbed over oily hair with the help of a comb, it produces electrostatic force.         
  • When one balloon is rubbed over another balloon in which one of the balloons is rubbed with hair, the electrostatic force is produced.

One point to remember is that the electrostatic force is basically a non-contact force; there exists zero contact with an object which is either pulled away or pushed against each other.

Net electrostatic formula

The net electrostatic force formula is   F = (k q1 q2 )/r2.


       k = proportionality constant

       q1, q2= charges in contact (charges can be either – + or +- or – – or + +)

       r = distance separating the charges

This is the basic formula to evaluate electrostatic force.

This formula gives the magnitude of the net electrostatic force.

The direction of the net electrostatic force is given by ϴ = tan-1 (Fx/Fy)

Here the net electrostatic force on the charges is calculated by adding the individual vector forces that exert the same force on the other charge, that is, the force exerted by q1 on q2 and force exerted by charge q2 on the q1.

Using the above formula, any kind of electrostatic force can be calculated, and when there are two or more charges, the formula will change accordingly.

For example, when there are three charges, the net electrostatic force is given as

       F12 = (k q1 q2 )/r12;    F13 = (k q1 q3)/ r13

Net electrostatic force problem

              Let a system consist of two charges, q1=20 μC; q2=-30 μC separated by distance. Now calculate the net electrostatic force.

F= (k q1 q2)/r2

F= (9 x 109 x 20 x 10-6 x 30 x 10-6) / (10 x10)

F= 54 x 10-3 N

Since we are dealing with two charges, the force exerted on each other will be the same, so the negative sign on charge q2 will be neglected.

  Calculate the magnitude of the net electrostatic force on charge q1 due to the charges q2 and q3.

The force exerted by q2 on q1 is F12; since the charge is positive, they attract each other. F13 is the force exerted by q3 on q1. This is also called an attractive force. Here the force points are in different directions, so we the vector components to calculate the net electrostatic force.

The magnitude of the net electrostatic force is as given:

 The force exerted on q1 due to q2:

F12= 9 x 109 x 3 x 10-6 x 5 x10-6 / (0.10 x 0.10)

F= 13.5 x 10 N

The force exerted on charge q1 due to q3:

             F13 = 9 x 109 x 3 x 10-6 x 2 x 10-6 / (15 x 15)

             F13 = 2.4 N

How to Calculate Net Electrostatic Force

Electrostatics is the part of physics that deals with the study of a phenomenon where the charges are present in static equilibrium, i.e. when the charges move extremely slow. The one main reason for charges to be in equilibrium is that they move rapidly because of the strong electric force present.

The basic phenomenon in static electricity is that the charges are transferred from one body to another. The object that loses charge an electron becomes positively charged, and the one that gains an electron becomes negatively charged.

Let’s say we have two charges, one negative and the other positive. These two charges are showed by q1 and q2 . r be the distance separating the charges.  Here we calculate the Coulomb force since the charges are unlike; they attract each other. The direction of the force is different, but the magnitude is the same. And this is due to the fact that the coulombs force is a vector quantity.

The force exerted by charge q1 is denoted by F1, and the charge denoted by charge by q2 is denoted by F2. But we consider it on the whole as the force of attraction.

Force of attraction acting on charge q1 due to q2, so the force is written as F12. Similarly, the force of attraction acting on charge q2 is written as F21.

Now considering the above-given explanation, we now derive the net electrostatic force as

                           F =       k q1 q2r X r      

where k is the proportionality constant having the value 9 x 109.

This is the basic formula to calculate electrostatic force, and based on the problems given; the formula takes a change likely to be the magnitude and the angle of the net electrostatic force.


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