physics : class12 Right-hand rule : Torque on an Electric Dipole : Electrostatics MCQ Questions and Answers
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Right-hand rule
MCQ questions and answers.
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MCQ Questions
1. For an electric dipole in a uniform electric field, the torque is given by τ = p × E. According to the right-hand rule, in which direction does the torque point when p is along +x and E is along +y?
A.
+x direction
B.
+y direction
C.
+z direction
D.
-z direction
Correct Answer:
+z direction
Explanation:
Using the right-hand rule for p × E, point the fingers along +x and turn them toward +y; the thumb points along +z.
2. A dipole has its dipole moment p along +x, while the electric field E is along -y. What is the direction of the torque according to the right-hand rule?
A.
+z direction
B.
-z direction
C.
+x direction
D.
-y direction
Correct Answer:
-z direction
Explanation:
The torque is p × E. Curling the right-hand fingers from +x toward -y makes the thumb point in the -z direction.
3. In the xy-plane, the dipole moment points along +y and the electric field points along +x. What is the direction of the torque?
A.
+z direction
B.
-z direction
C.
+x direction
D.
+y direction
Correct Answer:
-z direction
Explanation:
For p × E = +y × +x, the right-hand rule gives the -z direction.
4. If the torque vector on an electric dipole points out of the plane of the page, in which direction does it point?
A.
Into the page
B.
Toward the top of the page
C.
Out of the page
D.
Toward the bottom of the page
Correct Answer:
Out of the page
Explanation:
By convention, a vector pointing out of the page is directed toward the observer. The right-hand thumb indicates this direction when the fingers curl counterclockwise on the page.
5. When the torque vector on a dipole is directed into the page, how do the fingers of the right hand curl when viewed from the front of the page?
A.
Counterclockwise
B.
Clockwise
C.
Straight upward
D.
Straight downward
Correct Answer:
Clockwise
Explanation:
Pointing the right-hand thumb into the page makes the curled fingers point clockwise as viewed from the front.
6. The dipole moment p points toward the right, and the electric field E points upward on the page. Using τ = p × E, where does the torque point?
A.
Into the page
B.
Out of the page
C.
Toward the right
D.
Upward on the page
Correct Answer:
Out of the page
Explanation:
The right-hand fingers move from the rightward direction of p toward the upward direction of E, so the thumb points out of the page.
7. A torque vector points along +z, which is out of the page. What is the direction of the rotational tendency represented by this torque when viewed from the front?
A.
Clockwise
B.
Counterclockwise
C.
No rotational tendency
D.
Only upward translation
Correct Answer:
Counterclockwise
Explanation:
With the right-hand thumb pointing out of the page, the curled fingers show counterclockwise rotation.
8. A torque vector points along -z, which is into the page. What rotational direction does the right-hand rule indicate when viewed from the front?
A.
Counterclockwise
B.
Clockwise
C.
Motion only to the right
D.
Motion only upward
Correct Answer:
Clockwise
Explanation:
Pointing the right-hand thumb into the page causes the fingers to curl clockwise, indicating the rotational direction.
9. If the dipole moment points along +z and the electric field points along +x, what is the direction of the torque p × E?
A.
+x direction
B.
+y direction
C.
-y direction
D.
-z direction
Correct Answer:
+y direction
Explanation:
Using the right-hand rule, +z × +x gives +y. The thumb points along +y when the fingers turn from +z toward +x.
10. For a dipole with p along +y and E along +z, the torque direction is determined by p × E. Which direction does the right-hand rule give?
A.
+x direction
B.
-x direction
C.
+z direction
D.
-y direction
Correct Answer:
+x direction
Explanation:
Curling the right-hand fingers from +y toward +z makes the thumb point along +x, so the torque is in the +x direction.
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