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 ${10}^{6}N/C$ directed vertically downwards. The charge on the particle is: $(g=10m/s^2)$

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

Answer 1

The correct option is B $-5\times {10}^{-5}\mu C$

Force must be opposite to mg.
$\therefore$ Charge is negative.
As charge is stationary from free body diagram,
$\Rightarrow Eq=mg$
$\Rightarrow {10}^6\times q=5\times {10}^{-6}\times 10$
$\Rightarrow q=5\times {10}^{-11}C$
$\Rightarrow q=5\times {10}^{-5}\mu C.$
As force is in opposite direction of electric field q must be negative.
$q=-5\times {10}^{-5}\mu C.$