Electric Charges and Fields Class 12 Important Questions

Electric Charges and Fields — Class 12 Physics
Exam-focused practice questions covering electric charge, Coulomb's law, superposition, electric field, electric dipole, electric flux, Gauss's theorem and its applications.

How to Use This Question Set

Attempt the questions without looking at your notes first. For numerical problems, write the given data, formula, substitution and final unit. For derivations, show the main logical steps rather than writing only the final expression.

1. Very Short Answer Questions

1 Mark Questions

1. What is meant by quantisation of electric charge?
2. State the SI unit of electric charge.
3. State Coulomb's law for two point charges.
4. What is the principle of superposition of electric forces?
5. Define electric field intensity at a point.
6. What is the direction of the electric field due to a positive point charge?
7. Can two electric field lines intersect? Give a reason.
8. Define electric dipole moment and state its SI unit.
9. What is electric flux?
10. State Gauss's theorem in electrostatics.

2. Short Answer Questions

2 Mark Questions

1. Explain the conservation and quantisation properties of electric charge.
2. Two point charges are separated by a distance r. State how the electrostatic force changes if the distance is doubled.
3. Why is the electrostatic force called a central force?
4. Distinguish between electric field and electric field intensity.
5. Why do electric field lines never form closed loops in electrostatics?
6. What happens to the net force on a charge placed at a point where the electric field is zero?
7. State two characteristics of electric field lines.
8. Why is the electric field inside a uniformly charged spherical shell zero?

3. Conceptual and Application Questions

3 Mark Questions

1. Using the principle of superposition, explain how the net electric field at a point due to several point charges is determined.
2. Derive the expression for the electric field due to a point charge.
3. Explain the physical meaning of electric flux and write its expression for a uniform electric field through a plane surface.
4. Explain the electric field pattern of an electric dipole. Mention how the field-line pattern differs from that of a single point charge.
5. Derive the expression for the torque acting on an electric dipole placed in a uniform electric field.
6. Explain why the electric field at the surface of a charged conductor is normal to the surface in electrostatic equilibrium.
7. Using Gauss's law, obtain the electric field due to an infinitely long uniformly charged straight wire.
8. Using Gauss's law, obtain the electric field due to an infinite uniformly charged plane sheet.

4. Long Answer and Derivation Questions

5 Mark Questions

1. State Gauss's theorem and use it to derive the electric field due to a uniformly charged thin spherical shell for points (a) outside the shell and (b) inside the shell.
2. Derive the expression for the electric field on the axial line of an electric dipole. State the result for a distant point where the separation of charges is small compared with the distance.
3. Derive the expression for the electric field on the equatorial line of an electric dipole. State its direction with respect to the dipole moment.
4. Explain Coulomb's law in vector form and discuss the role of the unit vector joining the two charges.
5. Describe the principle of superposition and apply it to determine the net electric field at a point due to multiple point charges.

5. Numerical Practice

Numerical 1 — Coulomb's Law

Two point charges of +2 μC and −3 μC are placed 0.30 m apart in vacuum. Calculate the magnitude of the electrostatic force between them and state whether the force is attractive or repulsive.

Numerical 2 — Electric Field

A point charge of 5 μC is placed in vacuum. Calculate the electric field at a point 0.20 m from the charge.

Numerical 3 — Superposition

Two equal positive charges are placed symmetrically about the origin on the x-axis. Determine the direction of the resultant electric field at the origin. Explain your answer using superposition.

Numerical 4 — Dipole Moment

An electric dipole consists of charges ±4 μC separated by 5 cm. Calculate its dipole moment.

Numerical 5 — Electric Flux

A uniform electric field of magnitude 3 × 10⁴ N/C passes normally through a plane surface of area 0.02 m². Calculate the electric flux through the surface.

Numerical 6 — Gauss's Law

A closed Gaussian surface encloses a charge of 6 μC. Calculate the total electric flux through the surface.

6. Assertion–Reason Practice

For each question, choose the appropriate option:

(A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

(C) Assertion is true, but Reason is false.

(D) Assertion is false, but Reason is true.

1. Assertion: Electric field lines never intersect one another.
   Reason: At a point, the electric field has a unique direction.
2. Assertion: The electric field inside a uniformly charged thin spherical shell is zero.
   Reason: A Gaussian surface inside the shell encloses zero net charge.
3. Assertion: Electric flux is a scalar quantity.
   Reason: Electric flux is obtained from the dot product of electric field and area vector.
4. Assertion: The net electric field at the midpoint of two identical positive charges is zero.
   Reason: The electric fields produced by the two charges at the midpoint have equal magnitudes and opposite directions.
5. Assertion: The torque on an electric dipole in a uniform electric field is zero when the dipole is parallel to the field.
   Reason: The torque magnitude is given by pE sin θ.

7. Competency-Based / Case-Based Practice

Case Study: Electric Field and Gauss's Law

A charged spherical conductor is considered in electrostatic equilibrium. The charge resides on its outer surface, and a Gaussian surface can be selected to study the electric field at different distances from the centre.

1. What is the electric field inside the conductor in electrostatic equilibrium?
2. Which law is most directly useful for finding the electric field of a spherically symmetric charge distribution?
3. For a point outside a uniformly charged spherical shell, on what does the magnitude of the electric field depend?
4. What is the electric field immediately inside the charged thin spherical shell?

8. Diagram-Based Practice

1. Draw electric field lines for two equal positive point charges placed a finite distance apart.
2. Draw the electric field-line pattern for an electric dipole.
3. Draw a suitable Gaussian surface for an infinitely long uniformly charged straight wire and indicate the direction of the electric field.
4. Draw a Gaussian surface for a uniformly charged spherical shell and mark the regions where the electric field is zero and non-zero.

9. Quick Answer Check

Topic	Key Result
Coulomb's law	F = (1/4πε₀)|q₁q₂|/r²
Electric field	E = F/q₀
Point charge field	E = (1/4πε₀)q/r²
Dipole moment	p = q × 2a
Dipole torque	τ = pE sin θ
Electric flux	Φ = EA cos θ
Gauss's law	Φ = qenclosed/ε₀

10. Exam Practice Checklist

• Revise Coulomb's law and its vector form.
• Practise superposition of electric fields.
• Learn the properties and interpretation of electric field lines.
• Practise electric dipole field and torque questions.
• Understand electric flux and the area vector.
• Practise selecting appropriate Gaussian surfaces.
• Revise the three standard Gauss-law applications in this chapter.
• Show units and directions clearly in numerical answers.

Curriculum basis: CBSE Class XII Physics 2026–27. Chapter 1, Electric Charges and Fields, is part of Unit I: Electrostatics. The official curriculum groups Chapters 1–2 under a 16-mark unit allocation; CBSE's 2026–27 Class XII sample-paper and marking-scheme resources are published separately on the Academic website.