Question

The number of smallest units of charge in a charge of 1C is
A. $625\times {{10}^{10}}$
B. $625\times {{10}^{16}}$
C. $25\times {{10}^{12}}$
D. $265\times {{10}^{16}}$

Answer 1

As a very first step, one could read the question well and hence understand what is actually meant by smallest units of charge. Then you could also recall what one coulomb is and its significance. Then you could relate two of them and hence find the answer.

Complete step by step solution:
In the question we are asked to find the number of smallest units of charges that is found in a charge of 1 coulomb. As a very first step, one should understand what is meant by ‘smallest units of charge’. While defining charge we consider the smallest unit as the charge of an electron. So in the question, we are actually asked to find the number of electronic charge found in one coulomb.
One coulomb which is normally represented by C is the SI unit of charge. One may recall that one electronic charge is given by,
$e=1.6\times {{10}^{-19}}C$
So, in one coulomb we will have $\dfrac{1}{1.6\times {{10}^{-19}}}$electronic charges, that is $625\times {{10}^{16}}$electronic charges.
Hence, option B is found to be the correct answer.

Note: We could define one coulomb as the charge that is being transported by one ampere per second of current. So we could say that when the current is found to be one ampere, the number of electrons that is passing through the unit area of cross section in 1 second would be $625\times {{10}^{16}}$.