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 $+6 \mu C$ and $+10 \mu C$ kept at a certain distance repel each other with a force of $30 \ N$. If each charge is given an additional charge of $-8 \mu C$,the two charges:

Four charges of magnitude $-Q$ are placed at the four corners of a square,and a charge $q$ is placed at the center. If the system is in equilibrium,the value of $q$ is ......

Two identical conducting spheres having unequal positive charges $q_1$ and $q_2$ are separated by a distance $r$. If they are made to touch each other and then separated again to the same distance $r$,the electrostatic force between the spheres in this case will be (neglect induction of charges):

$A$ charge $Q$ is distributed over a line of length $L$. Another point charge $q$ is placed at a distance $r$ from the centre of the line distribution. Then the force experienced by $q$ is

Three point charges are placed at the corners of an equilateral triangle with sides of $10 \ cm$ as shown in the figure. The resultant force on the charge at $B$ will be: