Physics

The students will learn the following chapters in NCERT class 12 Physics. Physics numerical problems solutions are provided in detail and can be viewed by clicking on the links provided. This page gives you an overview of various chapters in the class 12 Physics syllabus. NCERT provides two books for class 12 physics. They are

1. Electric Charges and Fields: In this chapter, students will learn the fundamental concept of electric charge, including its types (positive and negative), and properties like additivity, conservation, and quantisation. They’ll understand the difference between conductors and insulators, and how charges behave on them. The chapter introduces Coulomb’s Law, explaining the force between two point charges and its vector nature. Students will also explore the concepts of electric field and electric field lines, and how to calculate the field due to multiple charges using the principle of superposition. Lastly, they’ll understand electric dipoles, electric flux, and Gauss’s law, laying the foundation for advanced electrostatics.

2. Electrostatic Potential And Capacitance: This chapter introduces the concept of electrostatic potential energy, explaining that it arises when a charge is moved in an electric field, particularly under conservative forces like the Coulomb force. It defines electrostatic potential as the work done per unit positive test charge to bring it from infinity to a point in the field, and elaborates on how potential is path-independent. The potential due to point charges, electric dipoles, and systems of charges is derived using superposition. The chapter also discusses equipotential surfaces, showing they are always perpendicular to electric field lines and no work is done moving charges along them. It explains the potential energy of a system of charges and extends this to configurations involving external electric fields, including the interaction energy of dipoles. Finally, the chapter introduces capacitors, their capacitance, and the behaviour of conductors and dielectrics in electrostatic fields, laying the groundwork for understanding electric energy storage.

3. Current Electricity: This chapter introduces the concept of electric current as the flow of charge through a conductor and explains how current is generated and maintained using sources like cells and batteries. It covers Ohm’s Law, which states that current through a conductor is directly proportional to the potential difference across it, and defines resistance and resistivity. The motion of electrons due to an applied electric field, called drift velocity, and its role in current generation is discussed in detail. The chapter also examines the temperature dependence of resistivity and distinguishes between conductors, insulators, and semiconductors based on their electrical properties. Fundamental circuit analysis techniques such as Kirchhoff’s rules, Wheatstone bridge, and power dissipation in resistors are presented. Overall, it builds the foundation for analyzing electric circuits and understanding the behaviour of materials under electric current.

4. Moving Charges and Magnetism: This chapter explores the intimate relationship between electricity and magnetism, beginning with Oersted’s discovery that an electric current produces a magnetic field. It introduces the concept of the Lorentz force, which acts on moving charges in electric and magnetic fields, and discusses how magnetic forces affect current-carrying conductors. The motion of charged particles in magnetic fields is examined, leading to applications like the cyclotron. The Biot-Savart law and Ampere’s circuital law are presented to calculate magnetic fields due to current elements and loops. The chapter also explains magnetic torque on current loops, magnetic dipoles, and the working of devices like the moving coil galvanometer, which measures electric current. Overall, it lays the foundation for understanding magnetic effects of current and their technological applications.

5. Magnetism and Matter: This chapter explores magnetism as a fundamental phenomenon, starting with the behaviour of bar magnets and the concept of magnetic field lines, which form continuous closed loops unlike electric field lines. It draws analogies between bar magnets and current-carrying solenoids, emphasizing the concept of magnetic dipoles and their behaviour in external magnetic fields, including torque and potential energy. Gauss’s law for magnetism is introduced, stating that the net magnetic flux through any closed surface is zero, reinforcing the non-existence of magnetic monopoles. The chapter also defines magnetisation (M), magnetic intensity (H), and susceptibility (χ), and introduces relationships among B, H, and M. Finally, it classifies materials as diamagnetic, paramagnetic, or ferromagnetic based on their response to magnetic fields, discussing unique behaviours like the Meissner effect in superconductors.

6. Electromagnetic Induction: Electromagnetic induction is the phenomenon where an electromotive force (emf) is generated in a circuit due to a changing magnetic flux. Faraday and Henry’s experiments showed that a relative motion between a magnet and a coil or between two coils can induce a current. Faraday’s law quantifies this effect, stating that the induced emf is equal to the negative rate of change of magnetic flux through the coil. Lenz’s law determines the direction of the induced emf, ensuring it opposes the change causing it, thus conserving energy. The chapter also introduces motional emf, mutual inductance, self-inductance, and the concept of energy stored in magnetic fields. Finally, it explains the working principle of an AC generator, where mechanical energy is converted into electrical energy through electromagnetic induction.

7. Alternating Current: This chapter introduces alternating current (AC), which varies sinusoidally with time and is preferred over direct current (DC) due to its easy voltage transformation using transformers and efficient long-distance transmission. It explains the behaviour of AC in resistors, capacitors, and inductors, highlighting how current and voltage differ in phase in each case. Concepts like reactance, impedance, and phasor diagrams are used to understand voltage-current relationships in complex circuits like LCR series circuits. The phenomenon of resonance is discussed, where maximum current occurs at a specific frequency when inductive and capacitive reactances cancel each other. Power in AC circuits is examined through the power factor, emphasizing that only resistors consume power, while inductors and capacitors store and return energy. Finally, the chapter details how transformers work on the principle of mutual induction to step up or down voltage in AC systems.

8. Electromagnetic Waves: This chapter explains how James Clerk Maxwell introduced the concept of displacement current to correct inconsistencies in Ampere’s law, unifying electricity and magnetism. He predicted the existence of electromagnetic waves, which are self-sustaining oscillations of electric and magnetic fields that travel through space at the speed of light. These waves are produced by accelerated charges and consist of electric and magnetic fields perpendicular to each other and to the direction of wave propagation. The chapter also explains how electromagnetic waves span a broad spectrum—from gamma rays to radio waves—each with distinct sources, uses, and characteristics. Key applications include communication (radio, TV), medicine (X-rays, gamma rays), and daily technologies (microwaves, infrared sensors). The electromagnetic wave’s velocity in a medium depends on its permittivity and permeability, affecting how light travels through different materials.

1. Ray Optics and Optical Instruments:

2. Wave Optics: Wave optics explains light as a wave phenomenon, contrasting Newton’s corpuscular theory. Huygens’ principle, which treats each point on a wavefront as a source of secondary wavelets, successfully derives laws of reflection and refraction. Young’s double-slit experiment demonstrated the interference of light, supporting the wave theory and showing conditions for constructive and destructive interference. Diffraction, the bending of light around obstacles, and polarization, which confirms the transverse nature of light waves, further reinforce the wave model. Maxwell’s theory unified light with electromagnetic waves, showing that light can propagate through a vacuum due to varying electric and magnetic fields. These phenomena—interference, diffraction, and polarization—mark the key distinctions of wave optics from geometrical optics.

3. Dual Nature of Radiation and Matter: This chapter explains how experiments like cathode ray discharge and the photoelectric effect led to the discovery of electrons and established the particle nature of light. It discusses the photoelectric effect in detail, highlighting how it cannot be explained by classical wave theory but is well explained by Einstein’s quantum theory, where light consists of photons. The chapter introduces Einstein’s photoelectric equation and shows how it explains various observations such as threshold frequency and instantaneous emission. It also presents the concept of photons having both energy and momentum, introducing the idea of the dual nature of radiation. Finally, it extends this duality to matter, presenting de Broglie’s hypothesis that particles like electrons also exhibit wave-like behaviour, giving rise to the concept of matter waves.

4. Atoms: This chapter explores the evolution of atomic models, starting from J.J. Thomson’s “plum pudding” model to Rutherford’s nuclear model, which proposed that atoms have a dense, positively charged nucleus. Rutherford’s gold foil experiment demonstrated that most of the atom is empty space, leading to the conclusion that electrons revolve around a tiny nucleus. However, this model couldn’t explain the stability of atoms or their discrete line spectra. Niels Bohr improved the model by introducing quantized electron orbits and postulated that electrons emit or absorb energy only when transitioning between these fixed orbits. Bohr’s model successfully explained the hydrogen spectrum but had limitations for multi-electron atoms. De Broglie later provided a wave-based explanation for Bohr’s quantization using the concept of matter waves.

5. Nuclei: This chapter explores the structure and properties of atomic nuclei, emphasizing that a nucleus is extremely small and dense, containing over 99.9% of an atom’s mass. It introduces atomic mass units, isotopes, isobars, and isotones, and discusses how protons and neutrons (collectively called nucleons) make up the nucleus. The concept of binding energy is explained using Einstein’s mass-energy equivalence, showing how nuclear stability arises from the energy required to separate nucleons. The nuclear force, which is strong, short-ranged, and independent of charge, holds the nucleus together. The chapter also covers radioactivity, nuclear fission (used in reactors and bombs), and fusion (the Sun’s energy source), highlighting their immense energy release compared to chemical reactions.