physics : class12 Zero torque condition : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Zero torque condition
MCQ questions and answers.
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MCQ Questions
1. An electric dipole placed in a uniform electric field experiences zero torque when the angle between its dipole moment and the electric field is
A.
0°
B.
45°
C.
90°
D.
60°
Correct Answer:
0°
Explanation:
The torque on a dipole is τ = pE sin θ. For θ = 0°, sin θ = 0, so the torque is zero.
2. An electric dipole has zero torque in a uniform electric field when its dipole moment is
A.
Perpendicular to the field only
B.
Parallel or antiparallel to the field
C.
At 45° to the field only
D.
At 60° to the field only
Correct Answer:
Parallel or antiparallel to the field
Explanation:
Since τ = pE sin θ, torque is zero for θ = 0° or 180°. These correspond to parallel and antiparallel orientations.
3. If the dipole moment of an electric dipole is aligned in the same direction as a uniform electric field, the torque on the dipole is
A.
Maximum
B.
Zero
C.
Half of its maximum value
D.
Infinite
Correct Answer:
Zero
Explanation:
When the dipole moment and electric field are in the same direction, θ = 0°, so τ = pE sin 0° = 0.
4. For an electric dipole in a uniform electric field, the torque becomes zero at an angle of
A.
30° only
B.
90° only
C.
180° only
D.
0° or 180°
Correct Answer:
0° or 180°
Explanation:
The torque is τ = pE sin θ. It vanishes when sin θ = 0, which occurs at 0° and 180°.
5. A dipole is placed in a uniform electric field with its dipole moment opposite to the field direction. The torque on the dipole is
A.
Zero
B.
Maximum
C.
Equal to pE
D.
Equal to pE/2
Correct Answer:
Zero
Explanation:
Opposite directions correspond to θ = 180°. Therefore, τ = pE sin 180° = 0.
6. Which expression gives the condition for zero torque on an electric dipole in a uniform electric field?
A.
pE sin θ = 0
B.
pE cos θ = 1
C.
pE tan θ = 1
D.
pE sin θ = 1
Correct Answer:
pE sin θ = 0
Explanation:
The torque on an electric dipole is τ = pE sin θ. Hence, zero torque requires pE sin θ = 0.
7. An electric dipole is placed at an angle of 180° to a uniform electric field. What is the value of sin 180° used in calculating its torque?
A.
1
B.
−1
C.
0
D.
1/2
Correct Answer:
0
Explanation:
Since sin 180° = 0, the torque τ = pE sin 180° is zero.
8. If the angle between the dipole moment and the electric field is 0°, the electric dipole is in which orientation for torque calculation?
A.
Perpendicular orientation
B.
Parallel orientation
C.
Random orientation
D.
45° orientation
Correct Answer:
Parallel orientation
Explanation:
An angle of 0° means that the dipole moment and electric field point in the same direction. In this orientation, the torque is zero.
9. For a dipole of nonzero dipole moment in a nonzero uniform electric field, which angle produces zero torque?
A.
15°
B.
45°
C.
90°
D.
180°
Correct Answer:
180°
Explanation:
With nonzero p and E, zero torque requires sin θ = 0. Among the given angles, θ = 180° satisfies this condition.
10. A dipole experiences zero torque in a uniform electric field when the line joining its charges is
A.
Perpendicular to the electric field only
B.
Parallel or antiparallel to the electric field
C.
At 30° to the electric field only
D.
At 45° to the electric field only
Correct Answer:
Parallel or antiparallel to the electric field
Explanation:
The dipole moment lies along the line joining the charges. When this line is parallel or antiparallel to the field, θ is 0° or 180°, giving zero torque.
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Zero torque condition
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