Electrostatic Force
All objects are made of atoms. Atoms are made up of electrons, protons, and neutrons. Electrons, protons, and neutrons have mass, but only the electron and the proton have charge. The proton has a positive charge and the electron has a negative charge.
If we place two electrons (both negatively charged) at an “r” distance, they will repel each other with a “F” force. This force depends on the “r” distance between the electrons and the charge of both. This “F” force is called the electrostatic force.
If instead of electrons we use protons, there is also a repulsion force because the charges are equal. (both positive). The force changes to attractive if instead of using two elements with equal charges, we use two elements with different charges. (an electron and a proton).
The electrostatic force is a force of attraction or repulsion, depending on the type of charges:
– Negative charge (e1) repels negative charge (e2).
– Positive charge (P1) repels positive charge (P2).
– Positive charge (P1) with negative charge (e2) attract each other.
– An electron (e) with a neutron (N) produces no force.
– A proton (P) with a neutron (N) produces no force.
Remember that the neutron (N) is “neutral”, it has no charge. In conclusion:
Charges of the same type repel each other,
different charges attract each other.
Note: Protons and electrons have equal but opposite charges, but the mass of the proton is nearly 2000 times the mass of the electron.
What is Coulomb’s Law?
The electrostatic force depends on the opposing electric charges and the distance separating them. The value of this electrostatic force is given by Coulomb’s law.
Where:
- F = electrostatic force acting on each charge Q1 and Q2.
- K = a constant that depends on the unit system and the environment in which the charges are located.
- r = distance between the charges.
In the MKS system and in vacuum:
Where
In the MKS system: k = 9 x 109 Newton-meter2/coulomb2
With this value of k, the charges are expressed in coulombs and the distance (R) is expressed in meters to give a resultant force in newtons.
- If the charges are opposite (+ and -), F will be negative, indicating attraction.
- If the charges are the same (+ and + or – and -), F will be positive, indicating repulsion.
Note: MKS system units: (meters, kilograms, seconds).