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

Answer: (C)

An electric dipole is an arrangement of two equal an 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 field and direction of dipole moment.
$\therefore \theta =0^{\circ }$
Hence, $U=-pE\cos 0^{\circ }=-pE$ (minimum)