The electric field at a point on equatorial plane at a distance r from the centre of a dipole having dipole moment

is given by,
(r≫ separation of two charges forming the dipole,

- permittivity of free space)

For an electric dipole in a non-uniform electric field with dipole moment parallel to direction of the field, the force F and torque τ on the dipole respectively are ___________.
Fill in the blank with the correct answer from the options given below.

Two charged particles, placed at a distance d apart in vacuum, exert a force F on each other. Now, each of the charges is doubled. To keep the force unchanged distance between the charges should be changed to _____________.
Fill in the blank with the correct answer from the options given below.

An electric dipole is placed at an angle of 30° with an electric field of intensity . It experiences a torque equal to 4 Nm. Calculate the magnitude of charge on the dipole, if the dipole length is 2 cm.