The intensity of the electric field required to keep a water drop of radius ${10^{ - 5}}\, cm$ just suspended in air when charged with one electron is approximately

Two point charges $a$ and $b$, whose magnitudes are same are positioned at a certain  distance from each other with a at origin. Graph is drawn between electric field strength at  points between $a$ and $b$ and distance $x$ from a $E$ is taken positive if it is along the line joining from to be. From the graph, it can be decided that 

In the given figure electric field at center $O$ due to section $AB$ of uniformly charged ring is $\overrightarrow E$. What will be electric field at $O$ due to section $ACB$ ?

The surface charge density of a thin charged disc of radius $R$ is $\sigma $. The value of the electric field at the centre of the disc is $\frac{\sigma }{{2\,{ \in _0}}}$. With respect to the field at the centre, the electric field along the axis at a distance $R$ from the centre of the disc

A positively charged ball hangs from a silk thread. We put a positive test charge ${q_0}$ at a point and measure $F/{q_0}$, then it can be predicted that the electric field strength $E$

A thin conducting ring of radius $R$ is given a charge $+Q.$ The electric field at the centre $O$ of the ring due to the charge on the part $AKB$ of the ring is $E.$ The electric field at the centre due to the charge on the part $ACDB$ of the ring is