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 are respectively $ (g=10\,m/s^2) $ :

• 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

The Correct Option is 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, $n=\frac{q}{e}=\frac{4.8 \times 10^{-19}}{1.6 \times 10^{-19}}=3$