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COMEDK Electrostatics — practice questions

Explore 55 free Electrostatics questions in COMEDK Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Electrostatics questions and exercises with answers

Showing questions 1–30 of 55.

What is the electric field at the centre of a hollow conducting sphere of radius $R$ carrying total charge $Q$?Read the answer and worked solution →The SI unit of electric charge is the:Read the answer and worked solution →Coulomb's law: force between two point charges is proportional to:Read the answer and worked solution →The value of k in Coulomb's law (in SI) is approximately:Read the answer and worked solution →Electric field strength at a point is defined as force per unit:Read the answer and worked solution →Total electric flux through a closed surface enclosing charge q (Gauss's law) is:Read the answer and worked solution →Electric field due to an INFINITE SHEET of charge with surface charge density σ:Read the answer and worked solution →The principle that charge can be neither created nor destroyed is:Read the answer and worked solution →Two point charges +2μC and -3μC are separated by 30 cm. The force on each (k = 9 × 10⁹):Read the answer and worked solution →Electric field due to a point charge q at distance r:Read the answer and worked solution →A charge of 1 C placed in an electric field of 100 N/C experiences force:Read the answer and worked solution →Electric potential V due to point charge q at distance r:Read the answer and worked solution →Potential difference between two points is 12 V. Work done to move 2 C between them:Read the answer and worked solution →Electric field INSIDE a conductor in electrostatic equilibrium is:Read the answer and worked solution →At an axial point of an electric dipole at distance r >> a (a = dipole half-length, p = qa·2 the dipole moment), E equals:Read the answer and worked solution →Number of charges that can be enclosed in a Gaussian surface in vacuum:Read the answer and worked solution →For a parallel plate capacitor with plate area A and separation d, the capacitance in vacuum:Read the answer and worked solution →Capacitance changes when DIELECTRIC of relative permittivity K is inserted:Read the answer and worked solution →Energy stored in a capacitor with charge Q and capacitance C:Read the answer and worked solution →Two charges +q and +q are placed at corners of an equilateral triangle. The third corner has potential:Read the answer and worked solution →For a spherical conductor of radius R carrying charge Q, the potential AT THE SURFACE equals:Read the answer and worked solution →Equipotential surfaces around a point charge are:Read the answer and worked solution →Two capacitors 2 µF and 4 µF connected in SERIES across 12 V. Charge on each:Read the answer and worked solution →3 capacitors of 6 µF each in PARALLEL: total capacitance:Read the answer and worked solution →Two charged spheres each of radius R, charge Q, separated by distance d >> R. Force F between them is:Read the answer and worked solution →Potential at center of square (side a) with charges +q, -q, +q, -q at corners (alternating):Read the answer and worked solution →Electric field inside a spherical cavity in a uniformly charged conductor is:Read the answer and worked solution →Find work done to bring a +2 µC charge from infinity to a point where V = 50 V:Read the answer and worked solution →A charged particle q is held at rest in vertical equilibrium in a uniform electric field E pointing upward. Charge-to-mass ratio q/m:Read the answer and worked solution →In a capacitor circuit, when a dielectric is inserted while voltage is HELD CONSTANT by battery, the CHARGE on capacitor:Read the answer and worked solution →

Worked practice questions

What is the electric field at the centre of a hollow conducting sphere of radius $R$ carrying total charge $Q$?

  1. $0$
  2. $\dfrac{kQ}{R^2}$
  3. $\dfrac{kQ}{R^3}$
  4. $\dfrac{kQ}{R}$
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Correct answer: A. $0$

Inside any closed conducting shell with all charge residing on its outer surface, Gauss's law applied to a sphere of radius $r < R$ encloses zero charge so $E = 0$ everywhere inside the cavity.

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The SI unit of electric charge is the:

  1. volt
  2. ampere
  3. coulomb
  4. ohm
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Correct answer: C. coulomb

Charge is measured in coulombs (C). 1 C = 1 A·s. The fundamental unit of charge is e = 1.6 × 10⁻¹⁹ C (proton/electron magnitude).

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Coulomb's law: force between two point charges is proportional to:

  1. 1/r
  2. 1/r² (inverse square)
  3. r²
  4. r
Show answer and solution

Correct answer: B. 1/r² (inverse square)

F = k q₁q₂/r². Inverse-square dependence on distance. Same mathematical form as Newton's gravity, but for charges.

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