Question

A polythene piece rubbed with wool is found to have negative charge of $3.6 \times 10^{-7} C$. If an electron has a mass $9.1 \times 10^{-31} kg$, find the mass transferred to polythene.

• A. $2.25 \times 10^{10} kg$
• B. $6.25 \times 10^{-18} kg$
• C. $2.05 \times 10^{-18} kg$
• D. $4.15 \times 10^{-18} kg$

Answer 1

Answer: (C)

$n=\frac{q}{e}=\frac{3.6 \times 10^{-7} C }{1.6 \times 10^{-19} C }=2.25 \times 10^{12}$
Therefore, mass transferred from wool to polythene,
$ M=n \times m_{e} =2.25 \times 10^{12} \times 9.1 \times 10^{-31}$
$=2.05 \times 10^{-18} kg$