Four charges are placed at the circumference of a dial clock as shown in the figure. If the clock has only an hour hand,then the resultant force on a charge $q_0$ placed at the center points in the direction which shows the time as (in $:30$)

Two point charges $+q_1$ and $+q_2$ repel each other with a force of $100 \ N$. $q_1$ is increased by $10 \%$ and $q_2$ is decreased by $10 \%$. If they are kept at their original positions, the change in the force of repulsion between them is:

Three identical charged balls,each of charge $2 \, C$,are suspended from a common point $P$ by silk threads of $2 \, m$ each (as shown in the figure). They form an equilateral triangle of side $1 \, m$. The ratio of the net electrostatic force on one charged ball to the force between any two charged balls is ...........

$N$ point charges are distributed into two groups and separated by a fixed distance. Then the ratio of maximum to minimum forces between the two groups is ($N$ is even and greater than $2$).

Three equal charges $+q$ are placed at the three vertices of an equilateral triangle centered at the origin. They are held in equilibrium by a restoring force of magnitude $F(r) = k r$ directed towards the origin,where $k$ is a constant. What is the distance of the three charges from the origin?

Three charges of each magnitude $100 \mu C$ are placed at the corners $A, B$ and $C$ of an equilateral triangle of side $4 \text{ m}$. If the charges at points $A$ and $C$ are positive and the charge at point $B$ is negative,then the magnitude of the total force acting on the charge at $C$ and the angle made by it with $AC$ are: