Two point charges $ + 3\,\mu C$ and $ + 8\,\mu C$ repel each other with a force of $40\,N$. If a charge of $ - 5\,\mu C$ is added to each of them, then the force between them will become....$N$

Check that the ratio $ke ^{2} / G m _{ e } m _{ p }$ is dimensionless. Look up a Table of Physical Constants and determine the value of this ratio. What does the ratio signify?

Explain vector form of Coulomb’s law and its importance. Write some important points for vector form of Coulomb’s law.

Four charges are placed at the circumference of the dial of a clock as shown in figure. If the clock has only hour hand, then the resultant force on a positive charge $q_0$ placed at the centre, points in the direction which shows the time as 

A negatively charged particle $p$ is placed, initially at rest, in $a$ constant, uniform gravitational field and $a$ constant, uniform electric field as shown in the diagram. What qualitatively, is the shape of the trajectory of the electron?

A simple pendulum of period $T$ has a metal bob which is negatively charged. If it is allowed to oscillate above a positively charged metal plate, its period will