An electric dipole,when placed in a uniform electric field $E$,will have minimum potential energy when the angle made by the dipole moment with the field $E$ is

Charges $-q$ and $+q$ located at $A$ and $B$,respectively,constitute an electric dipole. Distance $AB = 2a$,$O$ is the midpoint of the dipole and $OP$ is perpendicular to $AB$. $A$ charge $Q$ is placed at $P$ where $OP = y$ and $y >> 2a$. The charge $Q$ experiences an electrostatic force $F$. If $Q$ is now moved along the equatorial line to $P'$ such that $OP' = \frac{y}{3}$,the force on $Q$ will be close to: $\left( \frac{y}{3} >> 2a \right)$

$A$ dipole with an electric moment $\vec{p}$ is located at a distance $r$ from a long thread charged uniformly with a linear charge density $\lambda$. Find the force $F$ acting on the dipole if the vector $\vec{p}$ is oriented along the thread.

$A$ system of three charges is placed as shown in the figure. If $D >> d$,the potential energy of the system is best given by:

Four charges are placed at a distance $a$ from the origin as shown in the figure. The dipole moment of the configuration is:

The force on a charge situated on the axis of a dipole is $F$. If the charge is shifted to double the distance,the new force will be