The electric field due to a dipole at a distance $r$ on its axis is

Two point dipoles of dipole moments $\vec{p}_1$ and $\vec{p}_2$ are at a distance $x$ from each other,and $\vec{p}_1 \parallel \vec{p}_2$. The force between the dipoles is:

The electric field due to an electric dipole at a distance $r$ from its centre in the axial position is $E$. If the dipole is rotated through an angle of $90^{\circ}$ about its perpendicular axis,the electric field at the same point will be

Electric charges $q, q, -2q$ are placed at the corners of an equilateral triangle $ABC$ of side $l$. The magnitude of the electric dipole moment of the system is

An electric dipole is placed in a non-uniform electric field. Then,net

Two charged particles each of mass $9.8 \text{ g}$ and charges $+20 \mu\text{C}$ and $-20 \mu\text{C}$ are attached to the two ends of a massless and rigid uniform non-conducting rod of length $50 \text{ cm}$. This arrangement is held in a uniform electric field of $12.1 \text{ N/C}$,such that the rod makes a very small angle with the field direction. If the rod is set free,the minimum time needed for the rod to become parallel to the direction of the electric field is ................ seconds.