Question

There are n electrons of charge e on a drop of oil of density $\rho$. It is in equilibrium in an electric field E. Then radius of drop is

• A. ${\left[\frac{2neE}{4\pi \rho g}\right]}^{\frac{1}{2}}$
• B. ${\left[\frac{neE}{\rho g}\right]}^{\frac{1}{2}}$
• C. ${\left[\frac{3neE}{4\pi \rho g}\right]}^{\frac{1}{3}}$
• D. ${\left[\frac{2neE}{\pi \rho g}\right]}^{\frac{1}{3}}$

Answer 1

The correct option is C ${\left[\frac{3neE}{4\pi \rho g}\right]}^{\frac{1}{3}}$

W = F
Mg = Eq
$\frac{4}{3}\pi r^3\rho g=Ene$
$r={\left[\frac{3Ene}{4\pi \rho g}\right]}^{\frac{1}{3}}$