An atom contains electron and protons and as a result, there is an electric charge on it due to the balance or unbalance of these particles. Electron contains negative charges and protons contain a positive charge. Like charges repel each other and unlike charges attract each other. These particles create an electric field around then which exerts a force called Coulomb force. Those partials radiate the electric field in an outward direction. The strength of the field decreases in the proportion of square of the distance from the source if they move away from the nucleus.
Since protons are usually bound to nuclei; trapped inside atoms, they are not free to move as electrons are. So, an electric charge means the deficiency or surplus of electrons. When charges become unbalanced, electrons start flowing and an electric current is developed.
Early research on Electric charge
Benjamin Franklin originated the concept of the positive and negative value of charges in 1742. He collected charges from clouds containing thunderstorms through wet strings with the help of a kite. Franklin supported the model of single fluid of electric charge according to which an object has one charge it has an excess of fluid whereas an object has opposite charges if it has a deficit of charges. This way the positive and negative terms of electric charges were associated with excess and deficit of such charges.
The unit to measure electric charge “Coulombs” is named after a French scientist “Charles Augustin Coulomb”. The law states that like charges repel each other whereas unlike charges attract each other. Coulombs are defined as “the amount of electric charge taken by a current of 1 ampere in one second”.
Q = ne
n=number of electrons
e= charge on 1 electron (1.6 × 10-19C)
Properties of Electric Charge
An electric charge exhibits some basic properties that define their nature. They are briefly explained below:
- Conserved Quantity
- Additive in nature
- Quantization of charge
Let’s take a detailed look at each of the properties.
An electric charge is conserved in nature which means that it can neither be created nor be destroyed but can be transformed from one form to another through different methods such as inductions and conductions. As charging involves the simple phenomenon of rubbing two or more surfaces, directly moved from one body to another. We cannot produce a charge in a body but, with some conventional methods, we can ultimately move it to another body.
The principle of conservation states that the system remains constant if the charges are distributed accordingly. For example, if the system has a net charge of 10 coulombs, then it can be distributed among the system as 2C, 3C, 1C, 4C or in any other possible combination, but their net charge will always remain 10C.
Let’s look at another example. A neutron sometimes decays in nature to produce one electron and one proton. The system’s net charge will be zero as electrons and protons hold the same magnitude and opposite signs.
Additive in Nature
An electric charge is scalar because it has magnitude but, no direction. Charges are additive in nature which means that they are scalar and can be added directly into each other. We will explain this with the help of an example.
Consider a system comprising of two charges, namely q1 and q2. Now if you want to find the total charge of the system. It will be the algebraic sum of the number of charges i.e qn=q1 +q2. The same phenomena apply for any number of charges of the system.
qt= q1 + q2 + q3 + q4 + ………………………. + qn
Quantization of Charge
The property of quantization of charge signifies that electric charge is a quantized property and it can be expressed as the integral multiple of the charge(electron). Mathematically,
Q= charge on the body
n=number of charges
e=charge carried by electron or proton
The English scientist Faraday was the first to suggest the idea of the quantization of charge. He did this when he set forth his electrolysis experimental rules. Millikan actually demonstrated this principle in 1912 and proved it.
1 Ampere of Coulomb = 6 × 1018 electrons.
The quantization method can be used for measuring the total amount of charge present in an object and also for estimating the number of electrons or protons in an object.