In the Millikan's experiment,the distance between two horizontal plates is $2.5 \, cm$ and the potential difference applied is $250 \, V$. The electric field between the plates will be ....... $V/m$.

$A$ charged water drop of radius $0.1 \, \mu m$ is in equilibrium under an electric field. The charge on the drop is equivalent to the electronic charge. The intensity of the electric field is ........ $N/C$.

$A$ half ring of radius $R$ has a linear charge density of $\lambda$. The electric force on a $1\, C$ charge placed at the centre is

Four point positive charges of same magnitude $Q$ are placed at four corners of a rigid square frame in $xy$ plane as shown in the figure. The plane of the frame is perpendicular to the $z$-axis. If a negative point charge is placed at a distance $z$ away from the above frame $(z << L)$,then:

$A$ conducting sphere of radius $10 \; cm$ has an unknown charge. If the electric field $20 \; cm$ from the centre of the sphere is $1.5 \times 10^{3} \; N/C$ and points radially inward,what is the net charge (in $nC$) on the sphere?

$A$ charge of $1 \mu C$ each is placed on five corners of a regular hexagon of side $1 \ m$. The electric field at its centre is . . . . . . $N$/$C$.