physics : class12 Electric Dipoles in Insulators : Insulators : Electrostatics MCQ Questions and Answers
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Electric Dipoles in Insulators
MCQ questions and answers.
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MCQ Questions
1. An electric dipole consists of
A.
Two equal and opposite charges separated by a small distance
B.
Two equal positive charges separated by a distance
C.
A single positive charge only
D.
Two unequal negative charges at the same point
Correct Answer:
Two equal and opposite charges separated by a small distance
Explanation:
An electric dipole is formed by two equal and opposite charges separated by a small distance.
2. The electric dipole moment is directed from
A.
Positive charge to negative charge
B.
Negative charge to positive charge
C.
The midpoint toward the negative charge only
D.
The midpoint in a direction perpendicular to the charges
Correct Answer:
Negative charge to positive charge
Explanation:
By convention, the electric dipole moment points from the negative charge toward the positive charge.
3. The SI unit of electric dipole moment is
A.
Coulomb per metre
B.
Coulomb metre
C.
Newton per coulomb
D.
Volt per metre
Correct Answer:
Coulomb metre
Explanation:
Electric dipole moment is given by p = qd, so its SI unit is coulomb metre.
4. The magnitude of the electric dipole moment of charges +q and -q separated by distance d is
A.
q divided by d
B.
qd
C.
q plus d
D.
d divided by q
Correct Answer:
qd
Explanation:
The magnitude of dipole moment is the product of either charge and the separation between the charges: p = qd.
5. When an electric dipole is placed in a uniform electric field, the net force on it is
A.
Always equal to qE
B.
Always equal to 2qE
C.
Zero
D.
Always directed along the dipole moment
Correct Answer:
Zero
Explanation:
In a uniform electric field, equal and opposite forces act on the two charges of the dipole, giving zero net force.
6. The torque on an electric dipole of moment p in a uniform electric field E is
A.
pE sin theta
B.
pE cos theta
C.
p divided by E
D.
E divided by p
Correct Answer:
pE sin theta
Explanation:
The magnitude of torque on a dipole in a uniform electric field is tau = pE sin theta, where theta is the angle between p and E.
7. An electric dipole is in stable equilibrium in a uniform electric field when its dipole moment is
A.
Perpendicular to the electric field
B.
Opposite to the electric field
C.
Parallel to the electric field
D.
At an angle of 45 degrees to the electric field
Correct Answer:
Parallel to the electric field
Explanation:
The dipole is in stable equilibrium when its dipole moment is parallel to the electric field, because the torque is then zero and the potential energy is minimum.
8. The torque on an electric dipole is maximum when the angle between its dipole moment and the electric field is
A.
0 degrees
B.
30 degrees
C.
90 degrees
D.
180 degrees
Correct Answer:
90 degrees
Explanation:
Since tau = pE sin theta, the torque is maximum when sin theta equals 1, which occurs at 90 degrees.
9. The electric potential energy of a dipole in a uniform electric field is minimum when the dipole moment is
A.
Parallel to the electric field
B.
Perpendicular to the electric field
C.
Opposite to the electric field
D.
At 45 degrees to the electric field
Correct Answer:
Parallel to the electric field
Explanation:
The potential energy of a dipole is U = -pE cos theta, which is minimum when theta is zero and the dipole moment is parallel to the field.
10. An electric dipole placed in a non-uniform electric field can experience
A.
Only zero force
B.
Only torque and never force
C.
A net force as well as torque
D.
Neither force nor torque
Correct Answer:
A net force as well as torque
Explanation:
In a non-uniform electric field, the forces on the two charges may not cancel, so the dipole can experience both a net force and a torque.
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