physics : class12 Perpendicular dipole orientation : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Perpendicular dipole orientation
MCQ questions and answers.
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MCQ Questions
1. An electric dipole is placed perpendicular to a uniform electric field. If its dipole moment is p and the field strength is E, what is the torque on the dipole?
A.
0
B.
pE
C.
p/E
D.
E/p
Correct Answer:
pE
Explanation:
The torque on an electric dipole is τ = pE sin θ. For a perpendicular orientation, θ = 90°, so sin 90° = 1 and τ = pE.
2. When an electric dipole is oriented at 90° to a uniform electric field, the torque on it is:
A.
Minimum
B.
Zero
C.
Maximum
D.
Equal to the electric field only
Correct Answer:
Maximum
Explanation:
Since τ = pE sin θ and sin 90° = 1, the torque has its maximum value when the dipole is perpendicular to the field.
3. A dipole with dipole moment 2 C m is placed perpendicular to an electric field of 3 N/C. What torque acts on it?
A.
0 N m
B.
1.5 N m
C.
5 N m
D.
6 N m
Correct Answer:
6 N m
Explanation:
For a perpendicular dipole, τ = pE = (2)(3) = 6 N m.
4. An electric dipole is perpendicular to a uniform electric field. If the dipole moment is doubled while the field remains unchanged, the torque becomes:
A.
Half
B.
Unchanged
C.
Double
D.
Four times
Correct Answer:
Double
Explanation:
For perpendicular orientation, τ = pE. Therefore, doubling p doubles the torque.
5. An electric dipole of moment 4 × 10^-8 C m is placed perpendicular to a field of 5 × 10^4 N/C. The torque on the dipole is:
A.
2 × 10^-3 N m
B.
2 × 10^-4 N m
C.
9 × 10^-4 N m
D.
2 × 10^-12 N m
Correct Answer:
2 × 10^-3 N m
Explanation:
At 90°, τ = pE = (4 × 10^-8)(5 × 10^4) = 20 × 10^-4 = 2 × 10^-3 N m.
6. For a dipole placed perpendicular to a uniform electric field, the torque acts to:
A.
Rotate the dipole so that it tends to align with the field
B.
Move the dipole directly along the field
C.
Reduce the dipole moment to zero
D.
Make the electric field zero
Correct Answer:
Rotate the dipole so that it tends to align with the field
Explanation:
The torque on a perpendicular dipole tends to rotate its dipole moment toward the direction of the electric field.
7. A dipole is placed perpendicular to an electric field of 10 N/C and experiences a torque of 0.5 N m. What is its dipole moment?
A.
0.05 C m
B.
0.5 C m
C.
5 C m
D.
50 C m
Correct Answer:
0.05 C m
Explanation:
For a perpendicular dipole, τ = pE. Thus p = τ/E = 0.5/10 = 0.05 C m.
8. If the dipole moment of a perpendicular electric dipole is kept constant and the electric field is tripled, the torque will:
A.
Become one-third
B.
Remain unchanged
C.
Become three times
D.
Become nine times
Correct Answer:
Become three times
Explanation:
For a perpendicular dipole, τ = pE. With p constant, tripling E triples the torque.
9. The angle between the dipole moment and the electric field is 90°. Which expression gives the torque correctly?
A.
τ = pE cos 90°
B.
τ = pE sin 90°
C.
τ = p/E
D.
τ = E/p
Correct Answer:
τ = pE sin 90°
Explanation:
The general torque formula is τ = pE sin θ. For perpendicular orientation, θ = 90°, so τ = pE sin 90° = pE.
10. A perpendicular electric dipole has a dipole moment of 0.2 C m and experiences a torque of 1 N m. What is the electric field strength?
A.
0.2 N/C
B.
1.2 N/C
C.
5 N/C
D.
10 N/C
Correct Answer:
5 N/C
Explanation:
For a perpendicular dipole, τ = pE. Therefore, E = τ/p = 1/0.2 = 5 N/C.
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