An Overview of Ncert Books Class 12 Physics Chapter 1 Free Download
FAQs on Ncert Books Class 12 Physics Chapter 1 Free Download
1. What are the most important topics in Class 12 Physics Chapter 1, Electric Charges and Fields, for the CBSE 2025-26 board exams?
For the 2025-26 CBSE board exams, the high-priority topics from Electric Charges and Fields are:
Coulomb's Law and the Superposition Principle, especially for numerical problems involving multiple charges.
Electric field lines and their properties.
Derivations for the electric field of a dipole at axial and equatorial points.
Derivation for the torque on a dipole in a uniform electric field.
Gauss's Law and its applications to find the electric field for a uniformly charged infinite plane sheet, straight wire, and spherical shell.
2. What types of questions (1, 3, and 5 marks) are expected from Electric Charges and Fields?
Based on the CBSE pattern, the expected question distribution for this chapter is:
1-Mark Questions: These are typically MCQs or very short answer questions focusing on definitions like quantisation of charge, properties of electric field lines, or the SI unit of electric flux.
3-Mark Questions: These often include short derivations (like torque on a dipole), application-based numericals on Coulomb's law, or conceptual questions explaining 'why' a certain phenomenon occurs.
5-Mark Questions: These are usually reserved for long derivations, such as finding the electric field due to a dipole or the applications of Gauss's Law. They may also be a multi-part question combining a derivation with a numerical problem.
3. Which derivations from this chapter are frequently asked in board exams?
Students must thoroughly practise the following key derivations from Chapter 1, as they are frequently asked in exams:
Electric field intensity due to an electric dipole on its axial line.
Electric field intensity due to an electric dipole on its equatorial line.
Expression for the torque experienced by a dipole in a uniform external electric field.
Using Gauss's Law to derive the electric field for an infinitely long straight wire and a uniformly charged infinite plane sheet.
4. What kind of numericals are most important from Electric Charges and Fields?
The most important numericals are typically based on:
Coulomb's Law and Superposition Principle: Calculating the net force on a charge placed in a system of multiple charges, often arranged at the vertices of a square or triangle.
Electric Field: Finding the point on the line joining two charges where the net electric field is zero.
Electric Flux: Simple problems calculating the flux through a given surface using Gauss's Law.
Electric Dipole: Calculating torque or work done on a dipole in an external field.
5. How does the choice of a Gaussian surface affect the application of Gauss's Law in solving problems?
The choice of a Gaussian surface is critical because Gauss's Law is only useful for solving problems when the symmetry of the charge distribution allows for easy calculation of the electric field. An ideal Gaussian surface should have the following properties:
The electric field (E) should be normal to the surface and constant in magnitude at all points on it.
The electric field should be parallel to the surface, making the electric flux through that part of the surface zero.
A poor choice of surface makes the integral E.dS impossible to solve simply, defeating the purpose of using the law.
6. Why can't we use Coulomb's Law for a continuous charge distribution directly?
Coulomb's Law is defined for the force between two point charges. A continuous charge distribution (like a charged rod or sheet) consists of an infinite number of infinitesimal charges. To find the total force or field from such a distribution, we cannot simply use Coulomb's Law directly. Instead, we must use the principle of superposition combined with integration. We calculate the force due to a tiny element of charge (dq) and then integrate this expression over the entire distribution to find the net force.
7. Many students confuse electric flux and electric field. What is the key difference to remember for the exam?
The key difference lies in what they measure:
Electric Field (E) is a vector quantity that describes the force per unit charge at a specific point in space. It represents the strength and direction of the force a charge would experience at that point.
Electric Flux (Φ) is a scalar quantity that measures the total number of electric field lines passing through a given area. It represents the 'flow' of the electric field through a surface, not its strength at a single point.
For exams, remember that the field is about the cause (charge), while flux is about the effect over an area.
8. To score full marks, how should I present my answers for derivations in the board exam?
For derivations in the Class 12 Physics exam, a systematic presentation is crucial. Follow these steps for maximum marks:
Start with a clear, well-labelled diagram representing the problem.
State the aim or principle being used (e.g., "According to Gauss's Law...").
Show all mathematical steps clearly, explaining any assumptions or vector notations used.
Clearly state the final expression and put a box around it.
Mention any special cases or the direction of the final vector quantity if applicable.
9. Are the NCERT textbook questions sufficient for preparing the important questions from this chapter?
The NCERT textbook is the foundation for the CBSE curriculum and a significant number of board exam questions are based on its content. However, for comprehensive preparation, it is highly recommended to supplement your practice. You should solve:
All in-text solved examples and back exercises from the NCERT book.
Questions from the NCERT Exemplar, which contains higher-order thinking skills (HOTS) problems.
At least the last 5-7 years of previous year questions (PYQs) to understand the question patterns and marking trends.
