physics : class12 Field of Two Point Charges : Superposition Principle : Electrostatics MCQ Questions and Answers
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Field of Two Point Charges
MCQ questions and answers.
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MCQ Questions
1. Two point charges +q and −q are separated by a distance d. What is the magnitude of the electric field at the midpoint between them?
A.
0
B.
4kq/d²
C.
8kq/d²
D.
2kq/d²
Correct Answer:
8kq/d²
Explanation:
At the midpoint, each charge is at a distance d/2. The fields due to +q and −q are in the same direction, and each has magnitude kq/(d/2)² = 4kq/d². Therefore, the net field is 8kq/d².
2. Two equal positive charges +q are placed at equal distances from a point midway between them. What is the net electric field at the midpoint?
A.
0
B.
kq/d²
C.
2kq/d²
D.
4kq/d²
Correct Answer:
0
Explanation:
The two charges produce electric fields of equal magnitude at the midpoint, but in opposite directions. By the superposition principle, the fields cancel, giving a net field of zero.
3. At a point, two electric fields due to two point charges are equal in magnitude and perpendicular to each other. If each field is E, what is the resultant electric field?
A.
E/2
B.
E
C.
2E
D.
√2E
Correct Answer:
√2E
Explanation:
For two perpendicular fields, the resultant magnitude is √(E² + E²) = √2E.
4. Two point charges produce electric fields of 3 N/C and 4 N/C at a point, in the same direction. What is the net electric field at that point?
A.
1 N/C
B.
5 N/C
C.
7 N/C
D.
12 N/C
Correct Answer:
7 N/C
Explanation:
Since the two electric fields act in the same direction, their magnitudes add according to the superposition principle: 3 N/C + 4 N/C = 7 N/C.
5. Two point charges produce electric fields of 6 N/C and 2 N/C at a point in opposite directions. What is the magnitude of the resultant electric field?
A.
4 N/C
B.
8 N/C
C.
12 N/C
D.
3 N/C
Correct Answer:
4 N/C
Explanation:
For fields in opposite directions, the resultant magnitude is the difference of their magnitudes: 6 N/C − 2 N/C = 4 N/C.
6. Two equal positive charges are placed symmetrically on either side of a point on their perpendicular bisector. In which direction is the net electric field at that point?
A.
Along the perpendicular bisector, away from the charges
B.
Along the line joining the charges
C.
Toward the nearer charge
D.
The net field is always zero
Correct Answer:
Along the perpendicular bisector, away from the charges
Explanation:
The field components along the line joining the charges cancel by symmetry, while the components along the perpendicular bisector add. For positive charges, the net field points away from the charges along the perpendicular bisector.
7. Two point charges +q and +q are separated by a distance d. What is the direction of the net electric field at a point midway between them?
A.
Toward the left charge
B.
Toward the right charge
C.
Perpendicular to the line joining the charges
D.
There is no net electric field
Correct Answer:
There is no net electric field
Explanation:
At the midpoint, the two equal charges produce electric fields of equal magnitude in opposite directions. Hence, their vector sum is zero.
8. At a point, the electric field due to charge q₁ is E₁ and due to charge q₂ is E₂. According to the superposition principle, the net electric field is
A.
E₁ − E₂ only
B.
E₁ + E₂ as a vector sum
C.
E₁E₂
D.
E₁/E₂
Correct Answer:
E₁ + E₂ as a vector sum
Explanation:
The electric field due to two point charges is obtained by adding their individual electric field vectors. Their directions must therefore be considered.
9. Two point charges produce electric fields of 5 N/C and 5 N/C at a point in opposite directions. What is the resultant electric field?
A.
0 N/C
B.
5 N/C
C.
10 N/C
D.
25 N/C
Correct Answer:
0 N/C
Explanation:
Equal electric fields acting in opposite directions cancel each other under vector addition, so the net field is zero.
10. A point is equidistant from two equal positive charges. The electric field due to each charge at that point has magnitude E. If the fields are in the same direction, what is the net field?
A.
E/2
B.
E
C.
2E
D.
E²
Correct Answer:
2E
Explanation:
When the two equal electric fields point in the same direction, the net field is their sum: E + E = 2E.
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