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Capacitance Problems

This section provides 100 problems to test your understanding of capacitance, including calculations of capacitance for various geometries, series and parallel combinations, energy stored in capacitors, and the effects of dielectrics. Inspired by JEE Main, JEE Advanced, and NEET exam patterns, these problems are tailored for exam preparation, offering a mix of numerical, conceptual, and derivation-based challenges. NEET-style problems (66–100) are formatted as multiple-choice questions (MCQs) to match the exam’s objective format. Problems are organized by type to support progressive learning and build confidence in mastering electrostatics, a key topic for JEE/NEET success.

Numerical Problems

  1. A parallel plate capacitor has plates of area A=0.02m2 and separation d=0.002m in vacuum (ϵ0=8.85×1012C2/N·m2). Calculate the capacitance.

    • (a) 8.84×1011F
    • (b) 8.85×1011F
    • (c) 8.86×1011F
    • (d) 8.87×1011F
  2. A capacitor with capacitance C=15μF is charged to a potential difference V=100V. Calculate the charge stored on the capacitor.

    • (a) 1.49×103C
    • (b) 1.50×103C
    • (c) 1.51×103C
    • (d) 1.52×103C
  3. A spherical capacitor has inner radius a=0.1m and outer radius b=0.2m. Calculate the capacitance (ϵ0=8.85×1012C2/N·m2).

    • (a) 2.21×1011F
    • (b) 2.22×1011F
    • (c) 2.23×1011F
    • (d) 2.24×1011F
  4. A cylindrical capacitor has inner radius a=0.01m, outer radius b=0.02m, and length L=0.5m. Calculate the capacitance.

    • (a) 4.01×1011F
    • (b) 4.02×1011F
    • (c) 4.03×1011F
    • (d) 4.04×1011F
  5. Two capacitors C1=3μF and C2=6μF are connected in series. Calculate the equivalent capacitance.

    • (a) 1.99μF
    • (b) 2.00μF
    • (c) 2.01μF
    • (d) 2.02μF
  6. Three capacitors C1=2μF, C2=4μF, and C3=8μF are connected in parallel. Calculate the equivalent capacitance.

    • (a) 13.9μF
    • (b) 14.0μF
    • (c) 14.1μF
    • (d) 14.2μF
  7. Two capacitors C1=5μF and C2=10μF are in series, connected to a potential difference of 150V. Calculate the potential difference across C1.

    • (a) 99.9V
    • (b) 100.0V
    • (c) 100.1V
    • (d) 100.2V
  8. A capacitor C=25μF is charged to V=60V. Calculate the energy stored in the capacitor.

    • (a) 4.49×102J
    • (b) 4.50×102J
    • (c) 4.51×102J
    • (d) 4.52×102J
  9. A parallel plate capacitor has A=0.03m2, d=0.001m, and an electric field E=4000N/C between the plates. Calculate the energy density.

    • (a) 7.07×102J/m3
    • (b) 7.08×102J/m3
    • (c) 7.09×102J/m3
    • (d) 7.10×102J/m3
  10. A parallel plate capacitor has C=10μF. A dielectric with κ=2 is inserted while keeping the charge constant at Q=20μC. Calculate the new potential difference across the capacitor.

    • (a) 0.999V
    • (b) 1.000V
    • (c) 1.001V
    • (d) 1.002V
  11. A parallel plate capacitor has C=8μF, connected to a battery with V=50V. A dielectric with κ=3 is inserted while maintaining constant V. Calculate the new capacitance.

    • (a) 23.9μF
    • (b) 24.0μF
    • (c) 24.1μF
    • (d) 24.2μF
  12. A parallel plate capacitor has A=0.05m2, d=0.003m. Calculate the capacitance in vacuum.

    • (a) 1.47×1010F
    • (b) 1.48×1010F
    • (c) 1.49×1010F
    • (d) 1.50×1010F
  13. A capacitor C=12μF is charged to V=80V. Calculate the charge stored on the capacitor.

    • (a) 9.59×104C
    • (b) 9.60×104C
    • (c) 9.61×104C
    • (d) 9.62×104C
  14. A spherical capacitor has a=0.05m, b=0.1m. Calculate the capacitance.

    • (a) 1.11×1011F
    • (b) 1.12×1011F
    • (c) 1.13×1011F
    • (d) 1.14×1011F
  15. Two capacitors C1=4μF and C2=8μF are in series. Calculate the equivalent capacitance.

    • (a) 2.66μF
    • (b) 2.67μF
    • (c) 2.68μF
    • (d) 2.69μF
  16. Three capacitors C1=1μF, C2=2μF, C3=3μF are in parallel, connected to V=60V. Calculate the total charge stored.

    • (a) 3.59×104C
    • (b) 3.60×104C
    • (c) 3.61×104C
    • (d) 3.62×104C
  17. Two capacitors C1=6μF and C2=12μF are in series, connected to V=120V. Calculate the potential difference across C2.

    • (a) 39.9V
    • (b) 40.0V
    • (c) 40.1V
    • (d) 40.2V
  18. A capacitor C=30μF is charged to V=40V. Calculate the energy stored.

    • (a) 2.39×102J
    • (b) 2.40×102J
    • (c) 2.41×102J
    • (d) 2.42×102J
  19. A parallel plate capacitor has A=0.04m2, d=0.002m, E=3000N/C. Calculate the energy density.

    • (a) 3.97×102J/m3
    • (b) 3.98×102J/m3
    • (c) 3.99×102J/m3
    • (d) 4.00×102J/m3
  20. A capacitor C=5μF has Q=15μC. A dielectric with κ=2 is inserted (constant Q). Calculate the new potential difference.

    • (a) 1.499V
    • (b) 1.500V
    • (c) 1.501V
    • (d) 1.502V
  21. A capacitor C=4μF is connected to V=200V. A dielectric with κ=5 is inserted (constant V). Calculate the new energy stored.

    • (a) 0.799J
    • (b) 0.800J
    • (c) 0.801J
    • (d) 0.802J
  22. A parallel plate capacitor has A=0.1m2, d=0.005m. Calculate the capacitance in vacuum.

    • (a) 1.76×1010F
    • (b) 1.77×1010F
    • (c) 1.78×1010F
    • (d) 1.79×1010F
  23. A capacitor C=18μF is charged to V=70V. Calculate the charge stored.

    • (a) 1.259×103C
    • (b) 1.260×103C
    • (c) 1.261×103C
    • (d) 1.262×103C
  24. A spherical capacitor has a=0.02m, b=0.04m. Calculate the capacitance.

    • (a) 4.42×1012F
    • (b) 4.43×1012F
    • (c) 4.44×1012F
    • (d) 4.45×1012F
  25. Two capacitors C1=1μF and C2=2μF are in series. Calculate the equivalent capacitance.

    • (a) 0.666μF
    • (b) 0.667μF
    • (c) 0.668μF
    • (d) 0.669μF
  26. Four capacitors C1=5μF, C2=10μF, C3=15μF, C4=20μF are in parallel, connected to V=30V. Calculate the total charge stored.

    • (a) 1.499×103C
    • (b) 1.500×103C
    • (c) 1.501×103C
    • (d) 1.502×103C
  27. Two capacitors C1=2μF and C2=3μF are in series, then in parallel with C3=5μF. Calculate the equivalent capacitance.

    • (a) 6.19μF
    • (b) 6.20μF
    • (c) 6.21μF
    • (d) 6.22μF
  28. A capacitor C=40μF is charged to V=25V. Calculate the energy stored.

    • (a) 1.249×102J
    • (b) 1.250×102J
    • (c) 1.251×102J
    • (d) 1.252×102J
  29. A parallel plate capacitor has A=0.02m2, d=0.004m, E=2000N/C. Calculate the energy density.

    • (a) 1.76×102J/m3
    • (b) 1.77×102J/m3
    • (c) 1.78×102J/m3
    • (d) 1.79×102J/m3
  30. A capacitor C=6μF has Q=12μC. A dielectric with κ=4 is inserted (constant Q). Calculate the new potential difference.

    • (a) 0.499V
    • (b) 0.500V
    • (c) 0.501V
    • (d) 0.502V
  31. In a spacecraft power system, a capacitor has C=20μF, V=150V. A dielectric with κ=3 is inserted (constant V). Calculate the new capacitance.

    • (a) 59.9μF
    • (b) 60.0μF
    • (c) 60.1μF
    • (d) 60.2μF
  32. A parallel plate capacitor has A=0.08m2, d=0.004m. Calculate the capacitance in vacuum.

    • (a) 1.76×1010F
    • (b) 1.77×1010F
    • (c) 1.78×1010F
    • (d) 1.79×1010F
  33. A capacitor C=50μF is charged to V=20V. Calculate the charge stored.

    • (a) 9.99×104C
    • (b) 1.00×103C
    • (c) 1.01×103C
    • (d) 1.02×103C
  34. Two capacitors C1=7μF and C2=14μF are in series, connected to V=180V. Calculate the potential difference across C1.

    • (a) 119.9V
    • (b) 120.0V
    • (c) 120.1V
    • (d) 120.2V
  35. A capacitor C=10μF is charged to V=300V. A dielectric with κ=2 is inserted (constant V). Calculate the new energy stored.

    • (a) 0.899J
    • (b) 0.900J
    • (c) 0.901J
    • (d) 0.902J

Conceptual Problems

  1. What does capacitance measure?
  • (a) Charge stored per unit area
  • (b) Charge stored per unit potential difference
  • (c) Energy stored per unit charge
  • (d) Potential difference per unit energy
  1. What happens to the capacitance of a parallel plate capacitor if the separation between plates doubles?
  • (a) Doubles
  • (b) Halves
  • (c) Quadruples
  • (d) Quarters
  1. What is the key difference between capacitors in series and parallel?
  • (a) Series: same charge, parallel: same voltage
  • (b) Series: same voltage, parallel: same charge
  • (c) Series: same energy, parallel: same capacitance
  • (d) Series: same capacitance, parallel: same energy
  1. What happens to the energy stored in a capacitor if a dielectric is inserted while keeping the charge constant?
  • (a) Increases
  • (b) Decreases
  • (c) Remains the same
  • (d) Becomes zero
  1. What is the unit of capacitance in SI units?
  • (a) Farad
  • (b) Volt
  • (c) Joule
  • (d) Ohm
  1. What does a zero electric field inside a conductor imply for a capacitor?
  • (a) No charge on plates
  • (b) Uniform potential on plates
  • (c) Non-uniform potential on plates
  • (d) No field lines
  1. What is the physical significance of 12ϵ0E2?
  • (a) Energy stored in a capacitor
  • (b) Energy density in an electric field
  • (c) Capacitance of a capacitor
  • (d) Charge on a capacitor
  1. What does a dielectric do to the electric field inside a capacitor?
  • (a) Increases it
  • (b) Decreases it
  • (c) No effect
  • (d) Makes it zero
  1. What happens to the potential difference across a capacitor when a dielectric is inserted while keeping the voltage constant?
  • (a) Increases
  • (b) Decreases
  • (c) Remains the same
  • (d) Becomes zero
  1. What is the dimension of capacitance?
  • (a) [M1L2T4A2]
  • (b) [MLT1]
  • (c) [LT2]
  • (d) [ML2T1]
  1. What does a high capacitance indicate?
  • (a) High charge storage for a given voltage
  • (b) Low charge storage
  • (c) High voltage for a given charge
  • (d) No charge storage
  1. What is the significance of ϵ0Ad?
  • (a) Capacitance of a spherical capacitor
  • (b) Capacitance of a parallel plate capacitor
  • (c) Energy stored in a capacitor
  • (d) Charge on a capacitor
  1. What happens to the total charge in a series combination of capacitors?
  • (a) Same on each capacitor
  • (b) Different on each capacitor
  • (c) Zero on each capacitor
  • (d) Infinite on each capacitor
  1. What does the energy density in a capacitor depend on?
  • (a) Charge on the plates
  • (b) Electric field between the plates
  • (c) Area of the plates
  • (d) Separation between plates
  1. How do capacitors in spacecraft power systems function?
  • (a) Reduce charge
  • (b) Store energy for ion propulsion
  • (c) Increase distance
  • (d) Decrease field

Derivation Problems

  1. Derive the capacitance of a parallel plate capacitor C=ϵ0Ad.

  2. Derive the capacitance of a spherical capacitor C=4πϵ0abba.

  3. Derive the capacitance of a cylindrical capacitor C=2πϵ0Lln(b/a).

  4. Derive the equivalent capacitance for capacitors in series.

  5. Derive the equivalent capacitance for capacitors in parallel.

  6. Derive the energy stored in a capacitor U=12CV2.

  7. Derive the energy density in a capacitor u=12ϵ0E2.

  8. Derive the new capacitance of a capacitor with a dielectric C=κC0.

  9. Derive the effect of a dielectric on the electric field E=E0κ (constant Q).

  10. Derive the potential difference across a capacitor with a dielectric (constant V).

  11. Derive the total energy in a series combination of capacitors.

  12. Derive the total charge in a parallel combination of capacitors.

  13. Derive the potential difference across each capacitor in a series combination.

  14. Derive the energy stored in a capacitor with a dielectric (constant V).

  15. Derive the charge distribution in a parallel combination of capacitors.


NEET-style Conceptual Problems

  1. What is the unit of energy density in SI units?
  • (a) J/m3
  • (b) N/C
  • (c) J
  • (d) V
  1. What does a dielectric constant κ>1 indicate?
  • (a) Decreases capacitance
  • (b) Increases capacitance
  • (c) No effect on capacitance
  • (d) Reduces charge
  1. What happens to the total capacitance in a series combination?
  • (a) Greater than individual capacitances
  • (b) Less than the smallest capacitance
  • (c) Equal to the largest capacitance
  • (d) Zero
  1. What happens to the energy stored in a capacitor if the potential difference doubles?
  • (a) Doubles
  • (b) Halves
  • (c) Quadruples
  • (d) Quarters
  1. What is the dimension of energy density?
  • (a) [ML1T2]
  • (b) [MLT1]
  • (c) [LT2]
  • (d) [ML2T1]
  1. What does the area of the plates affect in a parallel plate capacitor?
  • (a) Electric field
  • (b) Capacitance
  • (c) Potential difference
  • (d) Energy density
  1. What is the role of a dielectric in a capacitor?
  • (a) Increases the electric field
  • (b) Decreases the electric field
  • (c) No effect on the field
  • (d) Reduces charge
  1. What happens to the charge on a capacitor in a parallel combination?
  • (a) Same on each capacitor
  • (b) Different, proportional to capacitance
  • (c) Zero on each capacitor
  • (d) Infinite on each capacitor
  1. Why does the energy density depend on the electric field?
  • (a) Due to u=12ϵ0E2
  • (b) Due to symmetry
  • (c) Due to field lines
  • (d) Due to charge quantization
  1. What is the unit of the dielectric constant κ?
  • (a) Unitless
  • (b) Farad
  • (c) Volt
  • (d) Joule
  1. What does a constant potential difference across a capacitor indicate?
  • (a) Variable charge
  • (b) Constant charge
  • (c) Variable field
  • (d) Zero field
  1. Which type of combination results in the same charge on each capacitor?
  • (a) Parallel combination
  • (b) Series combination
  • (c) Mixed combination
  • (d) No combination
  1. What is the direction of the electric field in a capacitor with a dielectric?
  • (a) Same as without dielectric, but reduced
  • (b) Opposite to the field
  • (c) Perpendicular to the plates
  • (d) Random
  1. What does a pseudo-force do in a non-inertial frame for capacitors?
  • (a) Affects perceived field
  • (b) Affects charge distribution
  • (c) Creates energy density
  • (d) Reduces capacitance
  1. What is the dimension of ϵ0?
  • (a) [M1L3T4A2]
  • (b) [MLT1]
  • (c) [LT2]
  • (d) [ML2T1]
  1. What is the role of capacitors in spacecraft power systems?
  • (a) Reduce charge
  • (b) Store energy for ion propulsion
  • (c) Increase distance
  • (d) Decrease field
  1. What happens to the potential difference across a capacitor with a dielectric (constant Q)?
  • (a) Increases
  • (b) Decreases
  • (c) Remains the same
  • (d) Becomes zero
  1. Why does the capacitance of a parallel plate capacitor depend on the area of the plates?
  • (a) Due to CA
  • (b) Due to symmetry
  • (c) Due to field lines
  • (d) Due to charge quantization
  1. What is the significance of 12Q2C?
  • (a) Electric field in a capacitor
  • (b) Energy stored in a capacitor
  • (c) Capacitance of a capacitor
  • (d) Charge on a capacitor
  1. What is the unit of energy stored in a capacitor?
  • (a) Joule
  • (b) Volt
  • (c) Farad
  • (d) Watt
  1. What does a zero energy density in a capacitor indicate?
  • (a) No electric field
  • (b) Maximum field
  • (c) No charge on plates
  • (d) Infinite charge
  1. What is the physical significance of 4πϵ0abba?
  • (a) Capacitance of a parallel plate capacitor
  • (b) Capacitance of a spherical capacitor
  • (c) Energy stored in a capacitor
  • (d) Charge on a capacitor
  1. Why does the energy stored in a capacitor increase with a dielectric (constant V)?
  • (a) Due to increased capacitance
  • (b) Due to decreased field
  • (c) Due to field lines
  • (d) Due to charge quantization
  1. What is the dimension of 1C?
  • (a) [ML2T4A2]
  • (b) [MLT1]
  • (c) [LT2]
  • (d) [ML2T1]
  1. How do dielectrics help in spacecraft capacitors?
  • (a) Reduce charge
  • (b) Increase capacitance for energy storage
  • (c) Reduce field
  • (d) Increase distance
  1. What is the role of separation d in a parallel plate capacitor?
  • (a) Cd
  • (b) C1d
  • (c) No dependence
  • (d) Exponential dependence
  1. What does a high energy density in a capacitor indicate?
  • (a) Low electric field
  • (b) High electric field
  • (c) No field
  • (d) Constant field
  1. What is the physical significance of Vd in a parallel plate capacitor?
  • (a) Electric field between plates
  • (b) Capacitance
  • (c) Energy density
  • (d) Charge on plates
  1. What is the dimension of QV?
  • (a) [M1L2T4A2]
  • (b) [MLT1]
  • (c) [LT2]
  • (d) [ML2T1]
  1. Why does the charge on a capacitor in a series combination remain the same?
  • (a) Due to conservation of charge
  • (b) Due to symmetry
  • (c) Due to field lines
  • (d) Due to charge quantization

NEET-style Numerical Problems

  1. A parallel plate capacitor has A=0.06m2, d=0.003m. Calculate the capacitance in vacuum.
  • (a) 1.76×1010F
  • (b) 1.77×1010F
  • (c) 1.78×1010F
  • (d) 1.79×1010F
  1. Two capacitors C1=2μF and C2=4μF are in series. Calculate the equivalent capacitance.
  • (a) 1.33μF
  • (b) 1.34μF
  • (c) 1.35μF
  • (d) 1.36μF
  1. A capacitor C=5μF is charged to V=100V. Calculate the energy stored.
  • (a) 2.49×102J
  • (b) 2.50×102J
  • (c) 2.51×102J
  • (d) 2.52×102J
  1. A capacitor C=8μF has Q=16μC. A dielectric with κ=2 is inserted (constant Q). Calculate the new potential difference.
  • (a) 0.999V
  • (b) 1.000V
  • (c) 1.001V
  • (d) 1.002V
  1. A capacitor C=3μF is connected to V=50V. A dielectric with κ=3 is inserted (constant V). Calculate the new energy stored.
    - (a) 1.124×102J
    - (b) 1.125×102J
    - (c) 1.126×102J
    - (d) 1.127×102J

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