NEET Physics: forces between multiple charges superposition principle Practice Questions
14 free multiple-choice questions on forces between multiple charges superposition principle (Electrostatics) for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.
Practice thousands more NEET questions in the app →Q1. Three charges q₁ = +5 μC, q₂ = -5 μC, and q₃ = +10 μC are placed such that q₁ and q₂ are separated by 1 cm and q₃ is placed outside the region between them. If q₁ and q₂ attract, and q₃ repels both, what is the net force on q₃?
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Correct answer: B — 2 × 10⁻⁹ N (repulsive)
q₁ and q₂ attract each other, and q₃ (positive) repels q₁ and q₂ (which are separated by q₃). Since q₃ is placed outside and repels the system, the net force acting on q₃ is repulsive, directed away from the charges.
Q2. Three charges, q₁ = +5 μC, q₂ = -2 μC, and q₃ = +3 μC, are arranged linearly. If q₁ is in the middle, and q₂ and q₃ are on opposite sides, which of the following statements is true regarding the forces?
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Correct answer: D — The forces exerted by q₂ and q₃ on q₁ are in opposite directions.
Since q₂ is negative and q₃ is positive, they exert forces on q₁ in opposite directions. Therefore, the net force is the difference between these two forces (superposition of forces in opposite directions).
Q3. Consider three charges q₁, q₂, q₃ placed in a line. If the force between q₁ and q₂ is attractive, and the force between q₂ and q₃ is repulsive, what must be true about the force between q₁ and q₃ for the net force to be zero?
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Correct answer: B — q₁ and q₃ must have opposite signs
For the net force to be zero (equilibrium), the forces must balance. If q₁ and q₃ have opposite signs, they will exert forces in opposite directions, allowing for a cancellation if the magnitudes are appropriately related.
Q4. Two point charges, q₁ = +3μC and q₂ = -2μC, are separated by a distance r. The magnitude of the electrostatic force between them is given by Coulomb's Law. If a third charge q₃ = +1μC is placed at the midpoint between q₁ and q₂, what is the net force experienced by q₃ due to q₁ and q₂?
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Correct answer: A — F₁ + F₂
According to the principle of superposition, the net force on q₃ is the vector sum of the forces exerted by q₁ and q₂. Since q₁ and q₂ have opposite signs, the forces will act in opposite directions, and the net force calculation depends on the specific geometry, but fundamentally involves summing the individual forces calculated by Coulomb's law.
Q5. The principle of superposition is applicable to electrostatic forces because:
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Correct answer: D — Electrostatic forces are vector quantities that can be added.
Electrostatic forces are vector quantities (forces) and can be added together mathematically, making the principle of superposition valid.
Q6. According to the principle of superposition for electrostatic forces, what is the net force experienced by a charge due to multiple point charges?
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Correct answer: A — The force is the algebraic sum of the individual forces acting on the charge.
The principle of superposition states that the net force acting on a charge due to a system of other charges is the vector sum (algebraic sum) of the individual forces exerted by each charge.
Q7. Three charges q₁ = +2μC, q₂ = -1μC, and q₃ = +3μC are placed along the x-axis at positions x=0, x=1 m, and x=2 m respectively. What is the net electrostatic force acting on q₂?
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Correct answer: C — 2μC/m
The net force on q₂ is the vector sum of the forces due to q₁ and q₃. Since q₁ (positive) repels q₂ (negative) and q₃ (positive) attracts q₂ (negative), the forces will have opposing directions, and the net force is the sum of these individual forces.
Q8. If N identical charges are placed at the same point, the total electrostatic force experienced by a test charge placed at that point is proportional to:
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Correct answer: C — The sum of the charges
Since the force is the superposition of individual forces (Coulomb's Law), if N identical charges are present, the total force is the sum of the forces, which is proportional to the sum of the charges present.
Q9. If a system of charges q₁ = +1 μC and q₂ = -1 μC are separated by a distance d, and a third charge q₃ = +1 μC is placed such that the forces between the pairs cancel out, what must be the relationship between the distances if the charges are collinear?
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Correct answer: D — d = x
For the forces to cancel (superposition principle), the forces must balance. If q₁, q₂, q₃ are collinear, the equilibrium condition requires F₁₃ = F₂₃, which implies q₁/r₁² = q₂/r₂² or q₁/r₁² = |q₃|/r₃² depending on the specific setup. For the simplest case where q₃ is between q₁ and q₂ and forces cancel, r₁ = r₂. If the setup implies simple cancellation of forces along a line, distances are proportional to charge magnitudes.
Q10. If the electric field at a point is the superposition of the fields produced by individual charges, what is the electric field due to a system of charges Q₁, Q₂, … at a point P?
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Correct answer: C — The vector sum of individual electric fields
The electric field is a vector quantity. According to the principle of superposition, the net electric field at any point is the vector sum of the electric fields produced by all individual charges.
Q11. Two charges, Q_A and Q_B, are separated by a distance d. A third charge Q_C is placed exactly midway between them. If Q_C is neutral, what is the net force exerted by Q_A and Q_B on Q_C (assuming they are collinear)?
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Correct answer: B — F_A - F_B
If Q_C is neutral, the forces exerted by Q_A and Q_B on it must balance and cancel out if they are equal in magnitude and opposite in direction, or the net force is zero if the configuration is symmetric. If Q_A and Q_B are opposite signs, the forces cancel.
Q12. A charge q is situated at a point O. If this charge is subjected to electric field E⃗₁ due to charge Q₁ and E⃗₂ due to charge Q₂, the total electric field E⃗ at point O is given by:
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Correct answer: C — E⃗₁ + E⃗₂
The principle of superposition for electric fields states that the net electric field at a point is the vector sum of the electric fields produced by all the individual sources.
Q13. Two point charges, +Q₁ and +Q₂, are placed in a vacuum. If they are separated by a distance r, the force between them is:
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Correct answer: D — Repulsive and proportional to Q₁Q₂/r².
Since both charges are positive, they exert a repulsive force on each other, which is given by Coulomb's Law, F = kQ₁Q₂/r².
Q14. Three point charges, q₁, q₂, and q₃, are placed on a line. If q₁ and q₂ repel each other, and q₂ and q₃ repel each other, what is the nature of the force between q₁ and q₃ if they are arranged in a straight line?
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Correct answer: C — Always repulsive.
If q₁ and q₂ repel, and q₂ and q₃ repel, the resulting force between q₁ and q₃ depends entirely on the signs and distances. If they are arranged q₁-q₂-q₃, the forces might oppose or reinforce depending on the charge values.
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