Charge is measured in coulombs and doubling the distance between two charges cuts the force to one fourth, so this Class 12 electrostatics sheet anchors on the unit and the inverse-square law. The key records N/C as the field unit and a no-field answer for inside a conductor.
Key Takeaways
The SI unit of charge is the coulomb (Q1).
Doubling the separation between charges quarters the force (Q2).
The key records N/C as the field unit.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.The SI unit of electric charge is the:
(a) coulomb(b) newton(c) volt(d) ampere
2.According to Coulomb's law, if the distance between two charges is doubled, the force between them becomes:
(a) double(b) one fourth(c) four times(d) the same
3.The electric field at a distance r from a point charge q is:
(a) kq/r(b) kq²/r²(c) kq/r²(d) kq/r³
4.The net electric flux through a closed surface depends only on the:
(a) charge outside the surface(b) shape of the surface(c) size of the surface(d) net charge enclosed by the surface
5.An electric dipole placed in a uniform electric field experiences:
(a) a torque only(b) a net force only(c) both a net force and a torque(d) neither a force nor a torque
6.The SI unit of electric field is:
(a) N/C(b) N·m(c) J/C(d) V·m
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.State Coulomb's law for the force between two point charges and write its vector form.
8.Define electric field at a point and give the SI unit of electric field.
9.State Gauss's law of electrostatics.
10.What is an electric dipole? Define its dipole moment and give its SI unit.
11.Define electric flux and give its SI unit.
12.Why is the net electric field inside a conductor zero in electrostatic equilibrium?
13.State three properties of electric field lines.
14.Write the expression for the electric field due to an infinite plane sheet of uniform surface charge density σ.
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.Two point charges +2 µC and +3 µC are separated by a distance of 0.5 m in air. Using F = kq₁q₂/r² with k = 9 × 10⁹ N·m²/C², find the force between them.
16.A charge of 5 µC is placed at a point where the electric field is 200 N/C. Using F = qE, find the force acting on the charge.
17.Using E = kq/r² with k = 9 × 10⁹ N·m²/C², find the electric field at a distance of 0.1 m from a point charge of 2 µC.
18.Using the fact that charge is quantised as q = ne with e = 1.6 × 10⁻¹⁹ C, find the number of electrons in a charge of 1 µC.
19.An electric dipole of dipole moment 2 × 10⁻⁶ C·m is placed in a uniform electric field of 10⁵ N/C. Using τ = pE, find the maximum torque that the field can exert on the dipole.
20.An infinite plane sheet carries a uniform surface charge density of 8.85 × 10⁻⁹ C/m². Using E = σ/2ε₀ and taking 1/(4πε₀) = 9 × 10⁹ N·m²/C², find the electric field near the sheet.
Answer Key
1. a) coulomb
2. b) one fourth
3. c) kq/r²
4. d) net charge enclosed by the surface
5. a) a torque only
6. a) N/C
7. Refer to solution guide.
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End of Worksheet
People Also Ask
What is the SI unit of electric charge?
The coulomb, option (a) in this worksheet (Q1).
What does doubling the distance between two charges do to the force?
It becomes one fourth, option (b) in this worksheet (Q2).
What is the unit of electric field?
N/C, from the answer key on this page.
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