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Electrostatics

Class 12 · Physics · 6 questions

Name: ____________________   Date: ____________

  1. Two point charges of 2 microcoulomb and 3 microcoulomb are 3 m apart in air. The force between them is about: (k = 9 x 10^9 N m2/C2)

    • A 6 x 10^-3 N
    • B 1.8 x 10^-2 N
    • C 2 x 10^-3 N
    • D 6 x 10^-6 N

  2. The electric field inside a charged conductor in equilibrium is:

    • A Infinite
    • B Maximum
    • C Equal to the surface field
    • D Zero

  3. The SI unit of electric field is:

    • A C/N
    • B J/C only
    • C N/C
    • D N m

  4. Two plates of a capacitor are 2 mm apart with a potential difference of 100 V. The field between them is:

    • A 5 x 10^4 V/m
    • B 2 x 10^5 V/m
    • C 200 V/m
    • D 5 x 10^2 V/m

  5. Capacitors in parallel have a combined capacitance equal to:

    • A The reciprocal of the sum
    • B The product
    • C The smallest one
    • D The sum of the capacitances

  6. Gauss's law relates the electric flux through a closed surface to the:

    • A Charge enclosed
    • B Outside charge
    • C Surface area only
    • D Mass

Answer key

1. A, 2. D, 3. C, 4. A, 5. D, 6. A

  1. F = k q1 q2 / r2 = 9 x 10^9 x 6 x 10^-12 / 9 = 6 x 10^-3 N.

  2. Free charges rearrange until the field inside is zero.

  3. Field is force per unit charge, newton per coulomb (or volt per metre).

  4. E = V / d = 100 / 0.002 = 5 x 10^4 V/m.

  5. For parallel capacitors C = C1 + C2 + ...

  6. Flux = enclosed charge / epsilon zero.