Question

A charged particle is suspended in equilibrium in a uniform vertical electric field of intensity $20000\, V / m$. If mass of the particle is $9.6 \times 10^{-16} kg$, the charge on it and excess number of electrons on the-particle respectively are $\left( g =10\, m / s ^{2}\right)$

• A. $4.8 \times 10^{-19} C,\, 3$
• B. $5.8 \times 10^{-19} C,\, 4$
• C. $3.8 \times 10^{-19} C,\, 2$
• D. $2.8 \times 10^{-19} C,\, 1$

Answer 1

Answer: (A)

Charge on the particle is given by
$q E =m g$ or $q=\frac{m g}{E}$
$=\frac{9.6 \times 10^{-16} \times 10}{20000}=4.8 \times 10^{-19}$
When there is an excess of $n$ electrons on the particle, then
$q=n e$
So, $n=\frac{q}{e}=\frac{4.8 \times 10^{-19}}{1.6 \times 10^{-19}}=3$