Question

A polythene piece rubbed with wood is found to have negative charge of $3.2 \times {10^{ - 7}}C$.
Estimate the number of electrons transferred from wood to polythene.
A. $2 \times {10^{12}}$
B. $3 \times {10^{12}}$
C. $4 \times {10^{12}}$
D. $5 \times {10^{12}}$

Answer 1

Hint-
Total charge will be the product of the number of electrons and the charge of a single electron.
That is,
$q = n \times e$
Where, $q$ is the total charge, $n$ is the number of electrons and $e$ is the charge of a single electron. charge of electron is $- 1.6 \times {10^{ - 19}}\,C$

Complete step-by-step answer:
Given,
Charge of polythene
$q = - 3.2 \times {10^{ - 7}}C$
Electrons are transferred from wood to polythene that is why polythene now has negative charge.
Let the no. of electrons transferred be n.
Then, total charge will be the product of the number of electrons and the charge of a single electron.
That is,
$q = n \times e$
Where, $q$ is the total charge, $n$ is the number of electrons and $e$ is the charge of a single electron.
We know that charge of electron is $- 1.6 \times {10^{ - 19}}\,C$
Therefore,
$n = \dfrac{q}{e} = \dfrac{{ - 3.2 \times {{10}^{ - 7}}}}{{ - 1.6 \times {{10}^{ - 19}}}} = 2 \times {10^{12}}$
This is the number of electrons transferred from wood to polythene.

So, the correct answer is option A.

Note:
Formula to remember-
$q = n \times e$
Where, $q$ is the total charge ,$n$ is the number of electrons and $e$ is the charge of a single electron.
charge of electron $e = - 1.6 \times {10^{ - 19}}\,C$.