Question

An electric dipole has the magnitude of its charge as `q` and its dipole moment is `p`. It is placed in a uniform electric field `E`. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively
A. `2qE` and minimum
B. `qE` and `pE`
C. zero and minimum
D. `qE` and maximum

Answer 1

Correct Answer - C
An electric dipole is an arrangment of two equal and opposite charges placed at a distance `2l`. The dipole is placed in electric field as such its dipole moment is in direction of electric field as shown in figure

Now force on the charge `q` is `F_(2) = qE` along the direction of `E` and force on charge `-q` is
`F_(1) = -qE` in the direction opposite to `E`
Since forces on the dipole are equal and opposite, so net force on the electric dipole is zero.

Now potential energy of the dipole,
`U = - pE cos theta`
where `theta` is the angle between direction of electric fieldand direction of dipole moment.
`theta = 0^(@)`
Hence, `U = -pE cos 0^(@) =-pE` (minimum)