Question

A charged particle of mass $5\times {10}^{-6}$ kg is held stationary in space by placing it in an electric field of strength ${10}^{6}N{C}^{-1}$ directed vertically downwards. The charge of the particle is $(g=10m{s}^{-2})$ :

• A. $-20\times {10}^{-4}\mu C$
• B. $-5\times {10}^{-5}\mu C$
• C. $5\times {10}^{-11}\mu C$
• D. $20\times {10}^{-5}\mu C$

Answer 1

Answer: (B)

$-5\times {10}^{-5}\mu C$

Gravitational force is acting downwards so, for equilibrium electric force should be upward as electric field is downward the charge should be negative and magnitude can be found out by equating gravitational force with electric force.

So, $mg=qE$

$q=\frac{mg}{E}$

$=\frac{5\times {10}^{-6}\times 10}{{10}^6}$

$=5\times {10}^{-11}C$

$=5\times {10}^{-5}\times {10}^{-6}C$

$=5\times {10}^{-5}\mu C$.

So, Charge will be $-5\times {10}^{-5}\mu C$.