Positive point charges are placed at the vertices of a star shape as shown in the figure. The direction of the electrostatic force on a negative point charge at the centre $O$ of the star is

Two small balls,each having a negative charge $Q$,are suspended from a fixed point by two identical insulating strings of length $L$. This entire arrangement is placed inside a satellite in a region where there is no gravity (weightless condition). The angle between the strings is ......... and the tension in each string is ......... Newtons.

The electrical force between two point charges is $200 \ N$. If we increase $10 \ \%$ charge on one of the charges and decrease $10 \ \%$ charge on the other,then the electrical force between them for the same distance becomes . . . . . . . . . . (in $N$)

When air is replaced by a dielectric medium of constant $K$,the maximum force of attraction between two charges separated by distance '$d$' is . . . . . . .

Two identical spheres are charged with equal charges and the force between them is $F$. If $50\%$ of the charge from one sphere is transferred to the other sphere,then the new force will be ........ $F$.

Three identical charges are placed on three vertices of a square. If the force acting between $q_1$ and $q_2$ is $F_{12}$ and between $q_1$ and $q_3$ is $F_{13}$,then $\frac{F_{13}}{F_{12}} = $ . . . . . . .