Question

(a) Explain the meaning of the statement ‘electric charge of a body is quantised’.
(b) Why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

Answer 1

Hint: In this question we will tell about how electron is the basic charge in nature and how the magnitude of charge on it is negligible as compared to the SI unit of charge i.e. Coulomb and other macroscopic charges that we are likely to encounter in real life.

Complete step by step answer:
Quantisation refers to there being a fixed minimum value and all quantities are integral multiples of that minimum value. Electric charge on a body can be acquired by addition or removal of electrons. Even addition or removal of protons can cause a charge on a body, but protons do not transfer over to cause charge on a body. So, almost always negative charge is caused by addition of electrons on a body and positive charge is caused by removal of electrons from the body. So, the charge on a body will always be an integral multiple of the charge of an electron. This is known as quantisation of charge.
The electric charge of an electron is very less and can be ignored for macroscopic charges which we will usually encounter, without any effect. Therefore, it can be assumed that electric charge is continuous for macroscopic charges. For reference the charge on an electron is 19 orders of magnitude lower than the SI unit of charge i.e. Coulomb. And even if we take up to 3 decimal places in coulomb, the charge can be considered continuous as the difference due to quantisation will be very low and would amount to nothing.

Note:
Knowledge of the magnitude of electric charge on an electron and electron being the basic charge in nature is important for this question. The student must also know that charges on macroscopic bodies usually arise due to transfer of electrons and very rarely due to transfer of protons.