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| Non-Rationalised Science NCERT Notes and Solutions (Class 12th) | ||||||||||||||
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Class 12th Physics NCERT Notes and Solutions (Non-Rationalised)
1. Electric Charges And Fields
This chapter introduces electrostatics, the study of charges at rest. It covers the fundamental properties of electric charge, including its quantisation (charge exists in discrete units of 'e') and conservation. The force between two point charges is quantitatively described by Coulomb's Law ($\textsf{F} = \frac{1}{4\pi\varepsilon_0} \frac{\textsf{q}_1\textsf{q}_2}{\textsf{r}^2}$). The concept of an Electric Field ($\vec{\textsf{E}}$) is introduced as the space around a charge where its influence can be felt, defined as the force per unit positive charge. A more powerful tool for calculating the electric field for symmetric charge distributions is Gauss's Law, which states that the total electric flux through a closed surface is equal to the net charge enclosed divided by the permittivity of free space ($\varepsilon_0$). Applications to find the field due to an infinite line charge, a uniformly charged infinite plane sheet, and a spherical shell are also discussed.
2. Electrostatic Potential And Capacitance
This chapter explores the energy aspects of electrostatics. It defines Electrostatic Potential ($\textsf{V}$) at a point as the work done in bringing a unit positive charge from infinity to that point. The relationship between electric field and potential ($\textsf{E} = -\frac{\textsf{dV}}{\textsf{dr}}$) is established, and the concept of equipotential surfaces is introduced. The second part of the chapter introduces Capacitance ($\textsf{C} = \frac{\textsf{Q}}{\textsf{V}}$), which is a measure of a conductor's ability to store electric charge and energy. It discusses the principle of a capacitor, its series and parallel combinations, and the energy stored in it ($\textsf{U} = \frac{1}{2}\textsf{CV}^2$). The effect of inserting a dielectric material between the plates of a capacitor, which increases its capacitance, is also explained in detail.
3. Current Electricity
This chapter shifts from static charges to charges in motion, defining electric current. The microscopic model of current is explained through the concept of drift velocity of electrons. The fundamental law governing current flow is Ohm's Law ($\textsf{V = IR}$). The chapter details the concept of electrical resistance ($\textsf{R}$) and its dependence on material (resistivity, $\rho$) and dimensions. To analyze complex circuits, Kirchhoff's laws—the Junction Rule (conservation of charge) and the Loop Rule (conservation of energy)—are introduced. The chapter also covers the internal resistance of a cell, combinations of resistors and cells, the heating effect of current, and electrical power.
4. Moving Charges And Magnetism
This chapter reveals the profound connection between electricity and magnetism: moving charges create magnetic fields. The Biot-Savart Law and Ampere's Circuital Law are introduced as fundamental tools for calculating the magnetic field produced by current-carrying elements and symmetric current distributions (like a straight wire, circular loop, solenoid, and toroid). The chapter then discusses the force on a moving charge in a magnetic field, described by the Lorentz force ($\vec{\textsf{F}} = \textsf{q}(\vec{\textsf{v}} \times \vec{\textsf{B}})$). This leads to the analysis of the force on a current-carrying wire and the torque on a current loop in a magnetic field, which forms the working principle of a moving coil galvanometer.
5. Magnetism And Matter
This chapter explores the magnetic behaviour of materials and the Earth's magnetic field. It begins with the concept of a bar magnet as an equivalent solenoid and discusses its magnetic field lines. It then delves into the Earth's magnetism and its components. The core of the chapter lies in the classification of magnetic materials into diamagnetic (feebly repelled), paramagnetic (feebly attracted), and ferromagnetic (strongly attracted) based on their response to an external magnetic field. The microscopic origin of this behaviour is explained. The concept of the hysteresis loop for ferromagnetic materials is introduced to explain properties like retentivity and coercivity, which are crucial for making permanent magnets and electromagnets.
6. Electromagnetic Induction
This chapter introduces the phenomenon of Electromagnetic Induction (EMI), where a changing magnetic field produces an electric current. This discovery is formalized by Faraday's laws of induction, which state that the magnitude of the induced electromotive force (emf) is proportional to the rate of change of magnetic flux. The direction of the induced current is given by Lenz's Law, which embodies the principle of conservation of energy. The chapter explains motional emf, eddy currents, and the concepts of self-inductance and mutual inductance. The working principle of the AC generator, a device that converts mechanical energy into electrical energy based on EMI, is also covered.
7. Alternating Current
This chapter focuses on Alternating Current (AC), where the current and voltage vary sinusoidally with time. Using the concept of phasors, it analyzes the response of circuits containing a resistor (R), an inductor (L), and a capacitor (C) to an AC source. It introduces the concepts of reactance (opposition offered by L and C) and impedance (total opposition in an LCR circuit). A key phenomenon discussed is resonance in a series LCR circuit, where the current becomes maximum at a specific frequency. The chapter also covers the concept of power in AC circuits and explains the working principle of a transformer, a crucial device for stepping up or stepping down AC voltages.
8. Electromagnetic Waves
This chapter unifies the concepts of electricity and magnetism by introducing Electromagnetic (EM) Waves. Based on Maxwell's equations and the concept of displacement current, it establishes that accelerating charges produce EM waves. These waves are transverse in nature, consisting of oscillating electric and magnetic fields perpendicular to each other and to the direction of wave propagation. The chapter highlights that all EM waves travel at the speed of light (c) in a vacuum. It presents the full electromagnetic spectrum, ranging from radio waves to gamma rays, detailing the properties, sources, and applications of each type of wave.
9. Ray Optics And Optical Instruments
This chapter, also known as geometric optics, treats light as rays travelling in straight lines. It covers the phenomena of reflection and refraction at plane and spherical surfaces. The mirror formula and the lens maker's formula are derived and used to determine the properties of images formed by mirrors and thin lenses. Important phenomena like total internal reflection (the principle behind optical fibres) and dispersion of light through a prism are explained. The chapter concludes by applying these principles to understand the working of optical instruments like the human eye, simple and compound microscopes, and telescopes, focusing on their magnifying power.
10. Wave Optics
This chapter explores phenomena that reveal the wave nature of light. It introduces Huygens' principle to explain the propagation of wavefronts and derive the laws of reflection and refraction. The principle of superposition is used to explain the phenomenon of interference, which is demonstrated through Young's double-slit experiment, resulting in a characteristic pattern of bright and dark fringes. The chapter also discusses diffraction, the bending of light waves around the edges of obstacles, and polarization, a property that confirms the transverse nature of light waves. Brewster's law and the use of polaroids are also covered.
11. Dual Nature Of Radiation And Matter
This chapter marks a transition to modern physics, introducing the revolutionary concept of wave-particle duality. It discusses the photoelectric effect, where electrons are emitted from a metal surface when light shines on it. The failure of classical wave theory to explain this effect led to Einstein's quantum theory, which proposed that light consists of discrete energy packets called photons ($\textsf{E = h}\nu$). Extending this duality, de Broglie's hypothesis proposed that matter particles (like electrons) also exhibit wave-like properties, with a wavelength given by $\lambda = \frac{\textsf{h}}{\textsf{p}}$. This was experimentally confirmed by the Davisson-Germer experiment, establishing the universal nature of this duality.
12. Atoms
This chapter delves into the structure of the atom. It begins with early models and focuses on Rutherford's nuclear model, which established the existence of a dense, positive nucleus. To overcome the shortcomings of Rutherford's model (atomic instability and inability to explain line spectra), the chapter introduces Bohr's model for the hydrogen atom. Bohr's three postulates—quantized stationary orbits, quantization of angular momentum, and the frequency condition for radiation—successfully explained the stability of the atom and the discrete spectral lines of hydrogen. The chapter derives expressions for the radius and energy of electron orbits based on this model.
13. Nuclei
This chapter focuses on the heart of the atom: the nucleus. It discusses the composition of the nucleus (protons and neutrons, collectively called nucleons) and its properties like size and density. The concepts of mass defect and nuclear binding energy ($\textsf{E}_\text{b} = \Delta \textsf{mc}^2$) are introduced, with the binding energy per nucleon curve explaining the stability of different nuclei. The chapter covers radioactivity, the spontaneous decay of unstable nuclei through the emission of alpha ($\alpha$), beta ($\beta$), and gamma ($\gamma$) radiation, governed by the law of radioactive decay. Finally, it explores nuclear energy released through nuclear fission (splitting a heavy nucleus) and nuclear fusion (fusing light nuclei).
14. Semiconductor Electronics: Materials, Devices And Simple Circuits
This chapter introduces the materials that form the backbone of modern electronics. It uses the energy band theory to classify materials into conductors, insulators, and semiconductors. It discusses intrinsic and extrinsic semiconductors, created by a process called doping to form p-type and n-type materials. The central device is the p-n junction, and its behaviour under forward and reverse bias is explained, leading to its application as a rectifier. Other key devices discussed include the photodiode, LED, and the bipolar junction transistor, whose use as an amplifier and switch is detailed. The chapter concludes with an introduction to digital electronics through logic gates (AND, OR, NOT).