Question

A drop of oil of density $\rho$ and radius $r$ carries a charge $q$ when placed in an electric field $E$, it moves upwards with a velocity $v$. If ${\rho }_0$ is the density of air, $\eta$ be the viscosity of the air, then which of the following force is directed upwards?

• A. $qE$
• B. $6\pi \eta rv$
• C. $\frac{4}{3}\pi r^3(\rho -{\rho }_0)g$
• D. None of these

Answer 1

The correct option is A $qE$

As positive charge at rest initially, moves in a direction of electric field, thus $F=qE$ is directed upwards and gravitational and viscous force is directed downwards.