physics : class12 Antiparallel dipole orientation : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Antiparallel dipole orientation
MCQ questions and answers.
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MCQ Questions
1. An electric dipole is placed antiparallel to a uniform electric field. What is the angle between the dipole moment and the electric field?
A.
0°
B.
90°
C.
180°
D.
45°
Correct Answer:
180°
Explanation:
In the antiparallel orientation, the dipole moment points exactly opposite to the direction of the electric field, so the angle is 180°.
2. What is the torque on an electric dipole placed antiparallel to a uniform electric field?
A.
pE
B.
pE/2
C.
Zero
D.
2pE
Correct Answer:
Zero
Explanation:
The torque on a dipole is τ = pE sin θ. For antiparallel orientation, θ = 180°, and sin 180° = 0, so the torque is zero.
3. An electric dipole in a uniform electric field has its dipole moment directed opposite to the field. What is the value of sin θ in the torque formula?
A.
0
B.
1
C.
-1
D.
1/2
Correct Answer:
0
Explanation:
For an antiparallel dipole, θ = 180°. Therefore, sin θ = sin 180° = 0, making the torque zero.
4. The antiparallel orientation of an electric dipole in a uniform electric field is an example of which type of equilibrium?
A.
Stable equilibrium
B.
Unstable equilibrium
C.
Neutral equilibrium
D.
No equilibrium is possible
Correct Answer:
Unstable equilibrium
Explanation:
Although the torque is zero at 180°, a small rotation produces a torque that moves the dipole farther from the antiparallel position. Hence, the equilibrium is unstable.
5. For an electric dipole in the antiparallel orientation, what happens to the torque if the dipole is given a small angular displacement?
A.
It remains zero
B.
It tends to restore the dipole to the antiparallel position
C.
It tends to rotate the dipole away from the antiparallel position
D.
It becomes independent of the electric field
Correct Answer:
It tends to rotate the dipole away from the antiparallel position
Explanation:
The antiparallel position is unstable. A small displacement creates a torque that increases the displacement rather than restoring the dipole to its original position.
6. What is the potential energy of an electric dipole in a uniform electric field when it is antiparallel to the field?
A.
-pE
B.
0
C.
pE
D.
-pE/2
Correct Answer:
pE
Explanation:
The potential energy is U = -pE cos θ. For the antiparallel orientation, θ = 180° and cos 180° = -1, so U = pE.
7. Compared with the parallel orientation, the antiparallel orientation of an electric dipole has what kind of potential energy in a uniform electric field?
A.
Lower potential energy
B.
Equal potential energy
C.
Higher potential energy
D.
Zero potential energy in all cases
Correct Answer:
Higher potential energy
Explanation:
The parallel orientation has U = -pE, while the antiparallel orientation has U = +pE. Therefore, the antiparallel orientation has higher potential energy.
8. A dipole of moment p is placed exactly opposite to a uniform electric field of magnitude E. What is the magnitude of the torque on it?
A.
pE
B.
2pE
C.
pE/2
D.
0
Correct Answer:
0
Explanation:
Using τ = pE sin θ and θ = 180° for the antiparallel orientation, the torque magnitude is pE sin 180° = 0.
9. In the antiparallel orientation, which direction does the dipole moment have relative to the electric field?
A.
The same direction
B.
The opposite direction
C.
A direction perpendicular to the field
D.
A direction at 45° to the field
Correct Answer:
The opposite direction
Explanation:
Antiparallel means that the dipole moment vector and the electric field vector lie along the same line but point in opposite directions.
10. If the electric field is increased while an electric dipole remains exactly antiparallel to it, what happens to the torque?
A.
It becomes nonzero immediately
B.
It remains zero
C.
It becomes equal to pE
D.
It changes direction but not magnitude
Correct Answer:
It remains zero
Explanation:
For the exact antiparallel orientation, θ remains 180°. Since τ = pE sin 180° = 0, increasing the field does not produce torque as long as the orientation remains exactly antiparallel.
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