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?

The unit of electric permittivity is

Two point charges $Q$ each are placed at a distance $d$ apart. A third point charge $q$ is placed at a distance $x$ from mid-point on the perpendicular bisector. The value of $x$ at which charge $q$ will experience the maximum $Coulomb's force$ is ...............

Two free point charges $+q$ and $+4q$ are a distance $R$ apart. $A$ third charge is so  placed that the entire system is in equilibrium. Then the third charge is :-

In general, metallic ropes are suspended on the carriers which take inflammable material. The reason is

Two identical charges $+Q $ are kept fixed some distance apart. A small particle $P $ with charge $q$ is placed midway between them. If $P$  is given a small displacement $\Delta$ , it will undergo simple harmonic motion if