physics : class12 Field of Three Point Charges : Superposition Principle : Electrostatics MCQ Questions and Answers
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Field of Three Point Charges
MCQ questions and answers.
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MCQ Questions
1. The electric field at a point due to three point charges is found by:
A.
Adding the electric fields due to all three charges vectorially
B.
Adding only the magnitudes of the three charges
C.
Multiplying the three individual electric fields
D.
Using the electric field of only the nearest charge
Correct Answer:
Adding the electric fields due to all three charges vectorially
Explanation:
According to the superposition principle, the net electric field due to three point charges is the vector sum of the electric fields produced by each charge separately.
2. Three point charges produce electric fields of 2 N/C, 3 N/C, and 4 N/C at a point, all in the same direction. What is the net electric field at that point?
A.
1 N/C
B.
5 N/C
C.
9 N/C
D.
24 N/C
Correct Answer:
9 N/C
Explanation:
Since all three electric fields act in the same direction, their magnitudes are added: 2 + 3 + 4 = 9 N/C.
3. Three point charges produce electric fields of 6 N/C east, 2 N/C west, and 4 N/C east at a point. What is the net electric field?
A.
8 N/C east
B.
12 N/C east
C.
4 N/C west
D.
0 N/C
Correct Answer:
8 N/C east
Explanation:
The eastward fields add to 10 N/C, while the westward field subtracts 2 N/C. Thus, the net field is 8 N/C east.
4. At a point, three charges produce electric fields of 5 N/C north, 5 N/C south, and 3 N/C east. What is the resultant electric field?
A.
3 N/C east
B.
10 N/C north
C.
5 N/C south
D.
13 N/C east
Correct Answer:
3 N/C east
Explanation:
The northward and southward fields cancel because they have equal magnitudes and opposite directions. The remaining field is 3 N/C east.
5. If the electric fields due to three point charges at a point are E1, E2, and E3, the net electric field is:
A.
E1 + E2 + E3 as a scalar in every case
B.
E1E2E3
C.
The vector sum of E1, E2, and E3
D.
E1 divided by E2 plus E3
Correct Answer:
The vector sum of E1, E2, and E3
Explanation:
Electric field has both magnitude and direction, so the fields due to three charges must be combined using vector addition.
6. Three identical positive point charges are placed symmetrically around a point. If their electric fields at the point are directed symmetrically and their vector sum is zero, the net electric field is:
A.
Equal to the field of one charge
B.
Zero
C.
Three times the field of one charge
D.
Always directed toward the nearest charge
Correct Answer:
Zero
Explanation:
By symmetry, the three equal electric-field vectors cancel vectorially at the point, giving a net electric field of zero.
7. A point is 1 m from each of three identical point charges. If the electric field due to each charge alone is 4 N/C in the same direction at that point, what is the net electric field?
A.
4 N/C
B.
8 N/C
C.
12 N/C
D.
16 N/C
Correct Answer:
12 N/C
Explanation:
Because the three individual electric fields have the same direction, the net field is 4 + 4 + 4 = 12 N/C.
8. When calculating the field due to three point charges, the electric field produced by one charge is calculated as if:
A.
The other two charges were absent
B.
The other two charges had twice their values
C.
All three charges were combined into one charge
D.
Only the signs of the other charges mattered
Correct Answer:
The other two charges were absent
Explanation:
The superposition principle requires finding the field due to each charge independently, as though the other charges were absent, and then adding the three fields vectorially.
9. Three point charges create electric fields of 7 N/C east, 7 N/C west, and 2 N/C north at a point. What is the net electric field?
A.
14 N/C east
B.
2 N/C north
C.
2 N/C south
D.
0 N/C
Correct Answer:
2 N/C north
Explanation:
The 7 N/C east and 7 N/C west fields cancel. Therefore, the remaining net electric field is 2 N/C north.
10. Three point charges produce electric fields of 3 N/C east, 4 N/C north, and 0 N/C at a point. What is the magnitude of the resultant electric field?
A.
1 N/C
B.
5 N/C
C.
7 N/C
D.
12 N/C
Correct Answer:
5 N/C
Explanation:
The eastward and northward fields are perpendicular. Their resultant magnitude is √(3² + 4²) = 5 N/C; the third charge contributes zero field at the point.
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