Electrical Energy of Two Point Charges and of a Dipole in an Electrostatic Field

A molecule with a dipole moment p is placed in an electric field of strength E. Initially the dipole is aligned parallel to the field. If the dipole is to be rotated to be anti-parallel to the field, find the work required to be done by an external agent. 

The angle at which maximum torque is exerted by the external uniform electric field on the electric dipole is ______.

A dipole is placed in a uniform electric field, its potential energy will be minimum when the angle between its axis and field is ______ 

The dipole moment of a water molecule is 6.3 x 10^-30 c·m. A sample of water contains 10²¹ molecules, whose dipole moments are all oriented in an electric field of strength 2.5 x 10⁵N/C. Calculate the work to be done to rotate the dipoles from their initial orientation θ₁ = 0° to one in which all the dipoles are perpendicular to the field, θ₂ = 90°.