Physics · Electric Charges And Fields · NEET
Yes for 4.8 x 10^-19 C, no for 5 x 10^-19 C. Charge must be Q = ne. Check: 4.8 x 10^-19 / 1.6 x 10^-19 = 3, a whole number, so it is allowed (n = 3). But 5 x 10^-19 / 1.6 x 10^-19 = 3.125, not a whole number, so that value is impossible. Always divide the given charge by e and see if you get an integer.
n is the number of extra or missing electrons on the body. If the body has 3 extra electrons, n = -3 and Q = -3e. If it lost 3 electrons, n = +3 and Q = +3e. So n just counts electrons, and it must be a whole number because you cannot add or remove half an electron.
Charge is truly discrete (it jumps in steps of e). But e = 1.6 x 10^-19 C is so tiny that in everyday charges (like 1 microcoulomb = about 6 x 10^12 electrons) the steps look smooth. So for large-scale problems we treat charge as continuous, but at the fundamental level it is quantised.
Experiments (Millikan's oil-drop experiment) showed all free charges are whole multiples of e = 1.6 x 10^-19 C, the charge on one electron or proton. Nothing free has ever been measured with less. This experimental fact is what quantisation of charge means for NEET.
No. Quarks do carry fractional charges (+2e/3 or -e/3), but quarks are never found free or alone; they always combine so the total is a whole multiple of e. Since NEET deals with free, isolated charges, the rule Q = ne with integer n holds perfectly.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the fact that any charge is always a whole-number multiple of the basic charge e, written Q = ne, with n an integer and e = 1.6 x 10^-19 C.
e = 1.6 x 10^-19 coulomb. It is the magnitude of charge on one electron or one proton and is the smallest free charge that exists.
Yes. n = 0 means a neutral body (equal positive and negative charge). Negative n means excess electrons (net negative charge); positive n means missing electrons (net positive charge).
Use n = Q / e. For example, a charge of 1.6 x 10^-6 C means n = 1.6 x 10^-6 / 1.6 x 10^-19 = 10^13 electrons transferred.
NTA sets direct one-mark questions asking which charge value is possible or how many electrons were transferred. Knowing Q = ne lets you solve them in seconds by dividing by e.
