JEE Main Physics: Electrical potential energy of point charges and dipoles Practice Questions
12 free multiple-choice questions on Electrical potential energy of point charges and dipoles (Electricity and Magnetism) for JEE Main 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 JEE Main questions in the app →Q1. The energy stored in an electric dipole of magnitude p oriented at an angle θ with respect to an external electric field E is:
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Correct answer: D — p E cos θ
The potential energy stored in a dipole in an external field is U = -p⃗ · E⃗ = -pE cos θ. This energy is minimized when θ=0 (parallel) and maximized when θ=180° (anti-parallel).
Q2. The potential energy associated with a system of electric dipoles is generally dependent on the angle between the dipoles and the external field. This dependence is governed by which physical principle?
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Correct answer: C — Principle of superposition
The interaction energy of dipoles depends on the geometry defined by the relative orientation of the dipoles and the external field, which is a direct consequence of the Principle of Superposition applied to the energy expressions.
Q3. The potential energy of an electric dipole placed in a uniform electric field is given by:
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Correct answer: B — -p E cos θ
The potential energy (U) of an electric dipole with dipole moment p in a uniform electric field E is U = -p⃗ · E⃗ = -pE cos θ, where θ is the angle between the dipole moment vector and the field vector.
Q4. If two identical point charges +q are separated by a distance r, the potential energy of the system is:
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Correct answer: C — k q² / r
The potential energy of two point charges is U = k (q₁ q₂)/r. For two identical charges q₁=q₂=q, the potential energy is U = k q²/r.
Q5. The electric potential energy of a system of two charges is inversely proportional to:
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Correct answer: D — The product of the charges and the distance
The electric potential energy between two point charges is U = k q₁ q₂ / r. This energy is inversely proportional to the separation distance r and directly proportional to the product of the charges q₁ q₂.
Q6. For an electric dipole placed in a uniform external magnetic field B⃗, the potential energy of the dipole is given by the interaction between the magnetic dipole moment and the field. If the magnetic moment is parallel to the field, the potential energy is:
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Correct answer: C — Minimum (most negative)
The potential energy of a magnetic dipole m⃗ in a magnetic field B⃗ is U = -m⃗ · B⃗. If m⃗ is parallel to B⃗ (θ=0°), U = -mB (Minimum energy/most negative value).
Q7. The electric potential energy of two point charges, q₁ and q₂, separated by a distance r, is given by:
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Correct answer: A — k q₁ q₂ / r
The electric potential energy (U) between two point charges is defined by the formula U = k (q₁ q₂)/r, where k = 1/4πε₀.
Q8. If two identical charges are placed in an electric field, the change in their potential energy is related to the work done by the electric field. This change is directly proportional to the change in which physical quantity?
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Correct answer: C — The distance between the charges
The change in potential energy (ΔU) is related to the work done (W = qV). For static charges, potential energy depends on the configuration (distance), and potential difference depends on the field. The change in potential energy is dependent on the spatial configuration, specifically the separation distance.
Q9. If two identical point charges +q and -q are separated by a distance r, the magnitude of the potential energy of this configuration is:
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Correct answer: A — -k q² / r
For two opposite charges +q and -q, the potential energy is U = k ((+q)(-q))/r = -k q²/r.
Q10. Two point charges, q₁ and q₂, are separated by a distance r. If the potential energy of the system is U, and the charges are brought closer by a distance Δr, the change in potential energy (ΔU) is given by:
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Correct answer: B — 1/4πε₀ q₁q₂/r - 1/4πε₀ q₁q₂/Δr
The potential energy of two point charges is U = 1/4πε₀ q₁q₂/r. When the distance changes by Δr, the change in potential energy is ΔU = U(Δr) - U(r) = 1/4πε₀ q₁q₂ ( 1/Δr - 1/r ). Option 0 represents the difference in potential energy calculation.
Q11. Three point charges +q, -q, and +q are placed at the vertices of an equilateral triangle with side length a. The total potential energy stored in the system is proportional to:
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Correct answer: C — 2q²/a
The potential energy of a configuration is the sum of the potential energies of all pairwise interactions. For three charges, the total potential energy involves the sum of U₁₂ + U₁₃ + U₂₃. The resulting expression simplifies to 2q²/a in this symmetrical case.
Q12. The electric potential energy of a charge q placed at a point where the electric field is E⃗ is determined by the potential V at that point. If the work done against the electric field to move the charge from infinity to this point is W, then W is equal to:
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Correct answer: B — qE
The work done by an external agent to bring a charge q from infinity (where V=0) to a point with potential V is W = qV. Since E = -dV/dr, W = qV is the fundamental relationship derived from the potential concept.
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