physics : class12 Torque components : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Torque components
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MCQ Questions
1. The torque on an electric dipole of dipole moment p placed in a uniform electric field E at an angle θ is given by:
A.
pE cos θ
B.
pE sin θ
C.
pE tan θ
D.
pE
Correct Answer:
pE sin θ
Explanation:
The magnitude of torque is the component of the electric force that tends to rotate the dipole, so τ = pE sin θ.
2. At what angle between the dipole moment and the electric field is the torque on an electric dipole maximum?
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
90°
Explanation:
Since τ = pE sin θ, the torque is maximum when sin θ = 1, which occurs at θ = 90°.
3. When an electric dipole is aligned parallel to a uniform electric field, its torque is:
A.
Maximum
B.
Zero
C.
pE
D.
pE/2
Correct Answer:
Zero
Explanation:
For θ = 0°, τ = pE sin 0° = 0. Therefore, no torque acts on the aligned dipole.
4. If the angle between an electric dipole and a uniform electric field is 30°, the torque magnitude is:
A.
pE
B.
pE/2
C.
√3pE/2
D.
2pE
Correct Answer:
pE/2
Explanation:
Using τ = pE sin θ and sin 30° = 1/2, the torque is τ = pE/2.
5. The torque vector on an electric dipole is directed:
A.
Along the dipole moment
B.
Along the electric field
C.
Perpendicular to both the dipole moment and electric field
D.
Opposite to the electric field only
Correct Answer:
Perpendicular to both the dipole moment and electric field
Explanation:
The torque is given by the vector product τ = p × E, so its direction is perpendicular to both p and E.
6. If the angle between the dipole moment and the electric field changes from 30° to 90°, the torque becomes:
A.
Half its previous value
B.
Twice its previous value
C.
Equal to zero
D.
Unchanged
Correct Answer:
Twice its previous value
Explanation:
At 30°, τ = pE/2, while at 90°, τ = pE. Thus, the torque becomes twice its value.
7. For an electric dipole in a uniform electric field, the component of the electric field perpendicular to the dipole moment is E sin θ. The torque is therefore:
A.
pE cos θ
B.
pE sin θ
C.
pE tan θ
D.
pE cot θ
Correct Answer:
pE sin θ
Explanation:
Only the component E sin θ perpendicular to the dipole produces torque, giving τ = p(E sin θ) = pE sin θ.
8. An electric dipole has dipole moment p and is placed perpendicular to a field E. Its torque magnitude is:
A.
Zero
B.
pE/2
C.
pE
D.
2pE
Correct Answer:
pE
Explanation:
For a perpendicular dipole, θ = 90°, so τ = pE sin 90° = pE.
9. If the dipole moment is reversed while the electric field remains unchanged, the direction of torque:
A.
Remains unchanged
B.
Reverses
C.
Becomes zero in every case
D.
Becomes parallel to the field
Correct Answer:
Reverses
Explanation:
Because τ = p × E, reversing the dipole moment reverses the direction of the torque vector.
10. For an electric dipole making an angle of 180° with a uniform electric field, the torque is:
A.
pE
B.
pE/2
C.
Zero
D.
2pE
Correct Answer:
Zero
Explanation:
At θ = 180°, τ = pE sin 180° = 0, so the torque is zero even though the dipole is oppositely aligned.
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