physics : class12 Uniform electric field : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Uniform electric field
MCQ questions and answers.
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MCQ Questions
1. An electric dipole of dipole moment p is placed in a uniform electric field E at an angle theta to the field. What is the magnitude of the torque on the dipole?
A.
pE cos(theta)
B.
pE sin(theta)
C.
pE tan(theta)
D.
pE
Correct Answer:
pE sin(theta)
Explanation:
The torque on an electric dipole in a uniform electric field is given by tau = pE sin(theta), where theta is the angle between the dipole moment and the field.
2. What is the torque on an electric dipole when its dipole moment is parallel to a uniform electric field?
A.
pE
B.
pE/2
C.
0
D.
2pE
Correct Answer:
0
Explanation:
For a parallel dipole, theta = 0 degrees, so tau = pE sin(0 degrees) = 0.
3. At what angle with a uniform electric field is the torque on an electric dipole maximum?
A.
0 degrees
B.
30 degrees
C.
90 degrees
D.
180 degrees
Correct Answer:
90 degrees
Explanation:
The torque is pE sin(theta), which is maximum when sin(theta) = 1. This occurs at theta = 90 degrees.
4. An electric dipole is placed perpendicular to a uniform electric field. If its dipole moment is p and the field is E, what is the torque magnitude?
A.
0
B.
pE
C.
p/E
D.
E/p
Correct Answer:
pE
Explanation:
For a perpendicular dipole, theta = 90 degrees. Therefore, tau = pE sin(90 degrees) = pE.
5. If the angle between an electric dipole and a uniform electric field is 30 degrees, the torque magnitude is:
A.
pE
B.
pE/2
C.
sqrt(3)pE/2
D.
0
Correct Answer:
pE/2
Explanation:
Using tau = pE sin(theta) and sin(30 degrees) = 1/2, the torque is pE/2.
6. The torque acting on an electric dipole in a uniform electric field tends to make the dipole moment:
A.
Perpendicular to the field
B.
Opposite to the field
C.
Parallel to the field
D.
Zero in magnitude
Correct Answer:
Parallel to the field
Explanation:
The torque tends to rotate the dipole so that its dipole moment aligns parallel to the uniform electric field.
7. If the electric field strength is doubled while the dipole moment and angle remain unchanged, the torque on the dipole becomes:
A.
Half
B.
Unchanged
C.
Twice
D.
Four times
Correct Answer:
Twice
Explanation:
Since tau = pE sin(theta), torque is directly proportional to the electric field strength. Doubling E doubles the torque.
8. If the dipole moment of an electric dipole is doubled in the same uniform electric field and at the same angle, its torque becomes:
A.
Half
B.
Unchanged
C.
Twice
D.
Four times
Correct Answer:
Twice
Explanation:
The torque is directly proportional to the dipole moment because tau = pE sin(theta). Therefore, doubling p doubles the torque.
9. An electric dipole placed in a uniform electric field experiences zero torque when the angle between its dipole moment and the field is:
A.
45 degrees
B.
60 degrees
C.
90 degrees
D.
0 degrees
Correct Answer:
0 degrees
Explanation:
The torque is zero when sin(theta) = 0. For the listed angles, theta = 0 degrees gives zero torque.
10. An electric dipole of moment 2 C m is placed in a uniform electric field of 3 N/C at 90 degrees. What is the 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:
Using tau = pE sin(theta), tau = 2 x 3 x sin(90 degrees) = 6 N m.
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