Master RBSE Class 12 Physics Chapter 1 (Electric Charges and Fields) with our complete, step-by-step solutions, key derivations, and exam-focused questions. Score high with this ultimate study guide!
Introduction: Your Gateway to High Scores in Physics
Welcome, RBSE Class 12 Science students! Physics is a crucial subject, and Chapter 1: Electric Charges and Fields (विद्युत आवेश तथा क्षेत्र) is the foundational cornerstone of Electrostatics. A deep understanding of this chapter is essential for acing your board exams and preparing for competitive exams like JEE and NEET.
This comprehensive guide provides complete solutions to all exercises, important derivations, and numerical problems from your RBSE Class 12 Physics curriculum, focusing on the latest rationalized NCERT syllabus.
Chapter 1 Overview: Electric Charges and Fields
This chapter introduces you to the fundamental concepts of electric charge and the forces they exert. Here are the key topics you need to master:
- Electric Charge: Properties (Quantization, Conservation), Charging methods.
- Coulomb’s Law: Force between two point charges, principle of superposition.
- Electric Field: Electric field intensity due to a point charge, and system of charges.
- Electric Field Lines: Properties and graphical representation.
- Electric Dipole: Dipole moment, Electric field due to a dipole on axial and equatorial lines, Torque on a dipole in a uniform external field.
- Continuous Charge Distribution: Linear, Surface, and Volume charge densities.
- Electric Flux and Gauss’s Law: Statement and applications (Electric field due to an infinitely long straight charged wire, a uniformly charged infinite plane sheet, and a uniformly charged thin spherical shell).
Complete Solutions: RBSE Class 12 Physics Chapter 1
Below are the solutions and explanations for the most critical theoretical and numerical problems, structured for maximum clarity and exam readiness.
1. Coulomb’s Law and Superposition Principle (Numericals)
| Concept | Key Formula | Solution Example (Based on Textbook Problems) |
| Coulomb’s Law | $F = \frac{1}{4\pi\epsilon_0} \frac{ | q_1 q_2 |
| Dielectric Effect | Fmedium=KFvacuum | Theory: If the medium’s dielectric constant K is increased, the force between the charges decreases. |
2. Electric Field and Dipole (Derivations & Definitions)
| Topic | Important Derivation/Formula | RBSE Exam Focus |
| Electric Field Intensity | E=q0F (Force per unit test charge) | Define E |
| Electric Dipole Moment | p | Define p |
| E on Axial Line | E | Practice the full derivation and state the direction. (High-Scoring 3/4 Marks) |
| Torque on Dipole | τ | Define torque and state the condition for stable and unstable equilibrium (θ=0∘ and θ=180∘). |
3. Gauss’s Law and its Applications (Must-Do Derivations)
Gauss’s Law is the most frequently asked topic for long answer questions (4-5 marks).
| Topic | Statement/Formula | Key Application Derivation |
| Electric Flux | ΦE=∫E | The total flux through a closed surface depends only on the enclosed charge. |
| Gauss’s Law | ΦE=∮E | Derivation 1 (Electric Field due to an Infinitely Long Straight Wire): E=2πϵ0rλ |
| Applications | Derivation 2 (Electric Field due to a Uniformly Charged Infinite Plane Sheet): E=2ϵ0σ (Constant Field) | Derivation 3 (Electric Field Inside/Outside a Spherical Shell): Ein=0, Eout=4πϵ01r2Q |
🔥 High-Ranking Strategy for RBSE Physics Chapter 1
To ensure you score maximum marks, follow this proven strategy:
| Strategy Area | Actionable Tip for Chapter 1 |
| Conceptual Clarity | Understand the distinction between electric field and electric flux. Know the properties of electric field lines (never intersect, start on positive, end on negative). |
| Derivations Mastery | Practice the three applications of Gauss’s Law and the dipole field on the axial line at least 5 times. Write them down from memory. |
| Numerical Practice | Focus on problems involving: Superposition of forces/fields (Square/Triangle problems) and Gauss’s Law calculations (Φ=q/ϵ0). |
| Previous Year Questions (PYQs) | Solve all RBSE previous year questions from this chapter (available on various educational platforms). Pay attention to 1-mark definition questions like Dielectric Constant and Electric Dipole Moment. |
| Chapter 1 | (Open) (Download chapter 1 ) |
Conclusion: Your Success is Charged!
RBSE Class 12 Physics Chapter 1: Electric Charges and Fields is a high-scoring unit. By focusing on the core concepts, mastering the key derivations (especially Gauss’s Law applications), and diligently practising the numerical solutions provided here, you are well on your way to securing a top rank in your board exams.
Don’t just read—write, derive, and practice!