Question

A polythene piece rubbed with wool is found to have a negative charge of $3\times {10}^{-7}\text{C}$. The number of electrons transferred between the materials is:

• A. $3\times {10}^{-7}$ electrons from wool to polythene
• B. It is not possible to have $3\times {10}^{-7}\text{C}$ charges
• C. $1.875\times {10}^{12}$ electrons from wool to polyethene
• D. $3\times {10}^{-7}$ electrons from polythene to wool

Answer 1

The correct option is C $1.875\times {10}^{12}$ electrons from wool to polyethene

Given:
$|q|=3\times {10}^{-7}\text{C}$

From quantization principle,
$q=ne$
$\Rightarrow -3\times {10}^{-7}=\left(n\right)(-1.6\times {10}^{-19})$

$\Rightarrow n=\frac{3\times {10}^{-7}}{1.6\times {10}^{-19}}$

$\therefore n=1.875\times {10}^{12}$

Since the number of electrons transferred $\left(n\right)$ is an integer. So, $1.875\times {10}^{12}$ electrons transferred from wool to polythene.

$\begin{array}{c}\text{Why this question ?}\\ \text{Caution: Net charge on a body must be integral multiple of}e\text{.}\\ \text{Thus be attentive for the value of}n.\\ n=\frac{q}{e}\end{array}$