A glass rod is rubbed with fur. After rubbing, the glass becomes slightly heavy. True or false.

The distance between electron and proton in a hydrogen atom is $0.53 {\mathrm{A}}^0$. Find the speed and frequency of revolution of electron round the proton.

$\left({\mathrm{m}}_{\mathrm{e}}=9.1\times {10}^{-31}\mathrm{kg}\right)$

Spherical conductor having a charge of $100 \mathrm{\mu C}$ is brought near another metallic sphere $\left(\text{of mass} 36 \mathrm{kg}\right)$ resting on earth's surface. What minimum distance of separation should be maintained so as to lift up the metallic sphere with uniform speed. What happens if the separation is more or less than the calculated value.

$\left(\text{assume} g=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$

Two identical charges are placed at a separation of $1.0m$. What should be the magnitude of each charge; so that each one repels the other with a force of $36kg wt.$

$\left(g=10m{S}^{-2}\right)$.