Question

An electric dipole having dipole moment $P = q \times 2\ell$ is placed in a uniform electric field 'E'. The dipole moment is along the direction of the field. The force acting on it and its potential energy are respectively

• A. qE and minimum
• B. qE and maximum
• C. 2qE and minimum
• D. zero and minimum

Hint:

In a uniform electric field, the net forces always cancel out completely ($F = 0$). Furthermore, aligning a dipole *with* the field lines ($\theta = 0^\circ$) is its most natural, relaxed orientation, meaning its potential energy is minimized in this stable equilibrium position!

Answer 1

The Correct Option is D

Step 1: Look at the force first.
A dipole has a $+q$ and a $-q$ charge. In a uniform field, one feels $+qE$ and the other feels $-qE$. These cancel, so the net force is zero.

Step 2: Recall the energy formula.
The potential energy is $U=-PE\cos\theta$, where $\theta$ is the angle between the dipole and the field.

Step 3: Use the given alignment.
Here the dipole points along the field, so $\theta=0$ and $\cos0=1$. That gives $U=-PE$, the lowest possible value.

Step 4: Conclusion.
Force is zero and energy is at its minimum. \[ \boxed{\text{zero and minimum}} \]