An uncharged capacitor is connected in series with a 4.0 kΩ resistor to a 12 V battery. What is the current at the instant the switch is closed?
Correct answer D. 3.0 mA
Topic / 30 questions
Electrostatics MCQs
Electrostatics MCQs cover Coulomb's law and the effect of a medium, electric field and field lines, the field of a charged sheet, electric potential, and the charging and discharging of a capacitor through a resistor. They suit MDCAT, ECAT and FSc revision, and every question on MCQs360 shows its correct answer instantly.
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A capacitor holding 100 μC discharges through a resistor. Approximately what charge remains after a time equal to two time constants?
Correct answer D. 14 μC
A 5.0 μF capacitor is charged through a 2.0 MΩ resistor. What is the time constant of the circuit?
Correct answer A. 10 s
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In a circuit where a capacitor charges through a resistor, the time constant RC is the time taken for the capacitor to reach about ____ of its final charge.
Correct answer C. 63%
A potential difference of 250 V is applied across two parallel plates 5.0 mm apart. What is the electric field between them?
Correct answer C. 5.0 × 10⁴ V/m
Equal and opposite charges +q and −q are a short distance apart. At the midpoint between them, ____.
Correct answer C. the potential is zero but the field is not zero
An electron is accelerated from rest through a potential difference of 500 V. What kinetic energy does it gain (e = 1.6 × 10⁻¹⁹ C)?
Correct answer A. 8.0 × 10⁻¹⁷ J
How much work is needed to move a charge of 2.0 μC between two points whose potential difference is 150 V?
Correct answer D. 3.0 × 10⁻⁴ J
What is the electric potential at a distance of 0.30 m from a point charge of 6.0 nC (k = 9.0 × 10⁹ N m² C⁻²)?
Correct answer B. 180 V
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Electric potential at a point is the work done per unit positive charge in bringing a charge from infinity to that point. Its SI unit, the volt, is equivalent to ____.
Correct answer A. J C⁻¹
Two large parallel plates carry equal and opposite uniform charges. What is the electric field in the region outside the plates?
Correct answer D. Zero
Two large parallel plates carry equal and opposite charge densities of magnitude 8.85 × 10⁻⁸ C/m². What is the electric field between them (ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²)?
Correct answer B. 1.0 × 10⁴ N/C
A large plane sheet carries a uniform surface charge density of 1.77 × 10⁻⁸ C/m². What is the electric field near it (ε₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²)?
Correct answer B. 1.0 × 10³ N/C
What does a region where electric field lines are drawn closer together indicate?
Correct answer A. A stronger electric field
How does the electric field near a large (effectively infinite) uniformly charged plane sheet vary with distance from the sheet?
Correct answer C. It is independent of the distance
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Electric field lines due to a system of charges ____.
Correct answer A. start on positive charges and end on negative charges
Why can two electric field lines never cross each other?
Correct answer B. The field at the crossing point would have two directions
Point charges +1.0 μC and +4.0 μC are 0.30 m apart. At what distance from the +1.0 μC charge, on the line joining them, is the electric field zero?
Correct answer B. 0.10 m
Charges of +2.0 μC and −2.0 μC are 0.20 m apart in air. What is the electric field at the midpoint between them (k = 9.0 × 10⁹ N m² C⁻²)?
Correct answer C. 3.6 × 10⁶ N/C
Two equal positive point charges are separated by a distance d. What is the electric field at the midpoint between them?
Correct answer D. Zero
About Electrostatics MCQs
Coulomb's law questions ask how the force changes when charges or separation change and how a medium of relative permittivity εᵣ reduces it. Electric field questions cover point charges, the field at the midpoint between like and unlike charges, field lines and the uniform field of a large charged sheet. Potential questions deal with the definition and unit of the volt, the potential of a point charge and the energy an electron gains when accelerated through a potential difference. The final group covers RC circuits: the time constant and how charge grows or decays during charging and discharging.
Key facts to remember
- Coulomb's law: F = kq₁q₂/r², with k = 1/4πε₀ ≈ 9.0 × 10⁹ N m² C⁻²; in a medium the force is reduced by a factor εᵣ.
- Electric field E = F/q₀; for a point charge E = kq/r².
- Near a large uniformly charged sheet, E = σ/2ε₀, independent of distance from the sheet.
- Electric potential of a point charge: V = kq/r; 1 volt = 1 joule per coulomb.
- A charge q accelerated through potential difference V gains kinetic energy qV; 1 eV = 1.6 × 10⁻¹⁹ J.
- Time constant τ = RC: a charging capacitor reaches about 63% of its final charge in one τ, and a discharging one falls to about 37%.
Exams that include Electrostatics MCQs
Pakistan
- MDCAT
- ECAT (UET)
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Electrostatics MCQs
- For ratio questions on Coulomb's law, write F ∝ q₁q₂/r² and change one factor at a time.
- Remember that at the midpoint between equal like charges the field is zero, while between equal unlike charges it is not.
- Learn that charge after n time constants of discharge is about Q₀ × (0.37)ⁿ, which answers many RC MCQs quickly.
- Keep electric field (a vector) and potential (a scalar) clearly separate when adding contributions from two charges.
Frequently asked questions
Which exams ask Electrostatics MCQs?
Electrostatics is part of the FSc physics syllabus, so its MCQs appear in MDCAT, ECAT (UET), NUMS and AKU entry tests and in FSc board papers. Students in India meet the same ideas in NEET and JEE Main, and Bangladeshi students in HSC and the medical admission test.
What is the time constant of an RC circuit?
The time constant τ = RC is the time for a charging capacitor to reach about 63% of its maximum charge, or for a discharging capacitor to fall to about 37% of its initial charge. A larger resistance or capacitance makes charging and discharging slower.
Last reviewed October 2026