Question

A body has a charge of one coulomb. The number of excess (or lesser) electrons on it from its normal state will be:
A. $\infty $
B. $1.6\times {{10}^{-19}}$
C. $1.6\times {{10}^{19}}$
D. $6.25\times {{10}^{18}}$

Answer 1

Hint: First we will discuss why it's generally the transfer of electrons that gives rise to a charge on a body. Then we will mention the amount of charge on an electron and then we will find how many electrons will be needed to give one coulomb of charge. That will be the number of extra electrons on the body with one coulomb of charge.

Complete step by step answer:
Electrons and protons are the two basic units of charge. Both have the charge of same magnitude, but the charge on the electron is taken as negative and on proton as positive. In an atom, protons are tightly bound inside the nucleus and very high energy is needed for them to break free. Whereas energy needed by electrons to break free of their bond to the atom is very less. Therefore, electrons break free and are generally the cause of charge transfer. The charge on one electron is given as $1.6\times {{10}^{-19}}$coulomb. For one coulomb number of electrons needed are $\dfrac{1}{1.6\times {{10}^{-19}}}=6.25\times {{10}^{18}}$.
So, this will be the number of excess electrons on the body for one coulomb of negative charge or lesser number of electrons on the body for one coulomb of positive charge.

Hence, the correct option is D.

Note:
There can be calculation mistakes made by the students in this question due to the very extreme nature of quantities in the question. Sometimes electrons exist freely inside a material such as conductors which makes them very suitable for current transfer. But they require some driving force to move them out of the conductor.