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NEET 2026
Exam
NEET
Year
2026
Subject
Physics
Chapter
Chapter

NEET 2026 · Physics · Chapter

A short electric dipole is placed near a long, straight, uniformly...

A short electric dipole is placed near a long, straight, uniformly positively charged wire. The dipole moment vector p
A short electric dipole is placed near a long, straight, uniformly positively charged wire. The dipole moment vector p⃗\vec{p} points towards the wire, as shown in the figure. If the dipole is free to move, in which direction will it begin to move and how will its electrostatic potential energy change?

Options

  1. ATowards the wire, as its potential energy will decrease.
  2. BTowards the wire, as its potential energy will increase.
  3. CAway from the wire, as its potential energy will decrease.
  4. DAway from the wire, as its potential energy will increase.

Correct answer

C. Away from the wire, as its potential energy will decrease.

Step-by-step solution

The electric field E⃗\vec{E} due to the uniformly positively charged wire points radially outward (away from the wire).

The magnitude of this electric field at a distance rr is E=λ2πϵ0rE = \dfrac{\lambda}{2\pi\epsilon_0 r}, which decreases as rr increases.

The dipole moment p⃗\vec{p} points towards the wire. This implies that the positive charge of the dipole is closer to the wire, while the negative charge is farther away.

Since the electric field is stronger closer to the wire, the repulsive force on the positive charge is greater in magnitude than the attractive force on the negative charge.

Therefore, the net force on the dipole is directed away from the wire, causing it to move away.

The electrostatic potential energy of the dipole is given by U=−p⃗⋅E⃗U = -\vec{p} \cdot \vec{E}.

Since p⃗\vec{p} points towards the wire and E⃗\vec{E} points away from it, the angle between them is 180∘180^\circ. Thus, U=−pEcos⁡(180∘)=pEU = -pE \cos(180^\circ) = pE.

As the dipole moves away from the wire, the electric field EE decreases, which means its potential energy UU will decrease. This is also consistent with the fact that a system free to move will always move in a direction that lowers its potential energy.

Answer: Away from the wire, as its potential energy will decrease.
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