Question

A body has $80\mu \text{C}$ of negative charge. The number of excess electrons in the body will be:

• A. $5\times {10}^{14}$
• B. $1.28\times {10}^{-17}$
• C. $80\times {10}^{-17}$
• D. $8\times {10}^{-5}$

Answer 1

The correct option is A $5\times {10}^{14}$

Given:
$q=-80\mu \text{C}=-80\times {10}^{-6}\text{C}$

On applying, $q=ne$

Here $e=-1.6\times {10}^{-19}\text{C}$

$\Rightarrow -80\times {10}^{-6}=\left(n\right)(-1.6\times {10}^{-19})$

$\Rightarrow n=\frac{80\times {10}^{-6}}{1.6\times {10}^{-19}}$

$\therefore n=5\times {10}^{14}$

Hence, option $\left(c\right)$ is the correct answer.
$\begin{array}{c}\text{Why this question ?}\\ \text{Tip: The charge}q\text{can take only}\\ \text{specific discrete values, which is an}\\ \text{integral multiple of charge of an}\\ \text{electron,}e=1.6\times {10}^{-19}\text{C}\\ \text{means}q=ne,n=0,1,2\dots \text{(both}\\ \text{positive and negative integers)}\end{array}$