physics : class12 Torque magnitude formula : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Torque magnitude formula
MCQ questions and answers.
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MCQ Questions
1. What is the magnitude of the torque acting on an electric dipole of dipole moment p placed in a uniform electric field E at an angle θ?
A.
pE sin θ
B.
pE cos θ
C.
pE tan θ
D.
pE
Correct Answer:
pE sin θ
Explanation:
The magnitude of torque on an electric dipole in a uniform electric field is given by τ = pE sin θ, where θ is the angle between the dipole moment and the electric field.
2. An electric dipole is placed parallel to a uniform electric field. What is the magnitude of the torque on it?
A.
pE
B.
pE sin 45°
C.
0
D.
2pE
Correct Answer:
0
Explanation:
For a parallel dipole, θ = 0°. Using τ = pE sin θ, τ = pE sin 0° = 0.
3. An electric dipole is placed perpendicular to a uniform electric field. What is the magnitude of the torque?
A.
0
B.
pE
C.
pE/2
D.
2pE
Correct Answer:
pE
Explanation:
For a perpendicular dipole, θ = 90°. Therefore, τ = pE sin 90° = pE.
4. If the dipole moment is 2 C m and the electric field is 3 N/C, what is the maximum torque on the dipole?
A.
1.5 N m
B.
5 N m
C.
6 N m
D.
9 N m
Correct Answer:
6 N m
Explanation:
Maximum torque occurs when θ = 90°, so τmax = pE = 2 × 3 = 6 N m.
5. A dipole of moment 4 C m is placed in an electric field of 5 N/C at an angle of 30°. What is the torque magnitude?
A.
5 N m
B.
10 N m
C.
20 N m
D.
40 N m
Correct Answer:
10 N m
Explanation:
Using τ = pE sin θ, τ = 4 × 5 × sin 30° = 20 × 0.5 = 10 N m.
6. At what angle between the dipole moment and the electric field is the torque magnitude maximum?
A.
0°
B.
30°
C.
60°
D.
90°
Correct Answer:
90°
Explanation:
The torque is τ = pE sin θ. Since sin θ is maximum and equal to 1 at 90°, the torque is maximum at θ = 90°.
7. If the angle between an electric dipole and a uniform electric field changes from 90° to 30°, how does the torque magnitude change?
A.
It becomes half its maximum value
B.
It becomes equal to its maximum value
C.
It becomes zero
D.
It becomes twice its maximum value
Correct Answer:
It becomes half its maximum value
Explanation:
At 90°, τmax = pE. At 30°, τ = pE sin 30° = pE/2, so the torque becomes half its maximum value.
8. An electric dipole experiences a torque of 8 N m in a field of 4 N/C when placed at 90°. What is its dipole moment?
A.
0.5 C m
B.
2 C m
C.
4 C m
D.
32 C m
Correct Answer:
2 C m
Explanation:
At 90°, τ = pE. Hence p = τ/E = 8/4 = 2 C m.
9. If the dipole moment is doubled while the electric field and angle remain unchanged, what happens to the torque magnitude?
A.
It becomes half
B.
It remains unchanged
C.
It becomes doubled
D.
It becomes four times
Correct Answer:
It becomes doubled
Explanation:
From τ = pE sin θ, torque is directly proportional to the dipole moment p when E and θ are constant.
10. If the electric field is doubled while the dipole moment and angle remain unchanged, what happens to the torque magnitude?
A.
It becomes half
B.
It remains unchanged
C.
It becomes doubled
D.
It becomes four times
Correct Answer:
It becomes doubled
Explanation:
From τ = pE sin θ, torque is directly proportional to the electric field E when p and θ are constant.
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