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| Classwise Science MCQ Questions with Solutions (Class 12th) | ||||||||||||||
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Class 12th Physics MCQ Questions
1. Electric Charges And Fields
This chapter introduces **electrostatics**, focusing on stationary electric charges and their interactions. It defines electric charge, its properties (quantisation, conservation), and the fundamental force between charges given by **Coulomb's Law** ($\textsf{F} = \textsf{k} \frac{\textsf{q}_1\textsf{q}_2}{\textsf{r}^2}$). The concept of **electric field** ($\vec{\textsf{E}}$) as the force per unit charge and its representation through field lines is explained. The electric dipole is discussed. **Gauss's Law** ($\oint \vec{\textsf{E}} \cdot \textsf{d}\vec{\textsf{A}} = \frac{\textsf{q}_\text{enclosed}}{\varepsilon_0}$) is introduced and applied to calculate electric fields for simple symmetric charge distributions, providing a powerful tool for analyzing electrostatic interactions.
2. Electrostatic Potential And Capacitance
Building upon the concept of electric fields, this chapter introduces **electrostatic potential** ($\textsf{V}$), defined as the potential energy per unit charge. The potential difference between points and its relation to the electric field ($\textsf{E} = -\frac{\textsf{dV}}{\textsf{dr}}$) are discussed. **Equipotential surfaces** are explained. The concept of **capacitance** ($\textsf{C} = \frac{\textsf{Q}}{\textsf{V}}$), the ability of a conductor to store charge, is central. **Capacitors**, devices for storing electrical energy, their combinations (series and parallel), and the **energy stored** ($\textsf{U} = \frac{1}{2}\textsf{CV}^2$) are covered, along with the effect of introducing **dielectric** materials between capacitor plates, enhancing charge storage capability.
3. Current Electricity
This chapter deals with the flow of electric charge, known as **electric current**. It defines current ($\textsf{I} = \frac{\textsf{dQ}}{\textsf{dt}}$) and the concept of **drift velocity**. **Ohm's Law** ($\textsf{V = IR}$), relating voltage, current, and resistance, is fundamental. Concepts like resistivity ($\rho$), conductivity ($\sigma = \frac{1}{\rho}$), and their temperature dependence are discussed. Series and parallel combinations of resistors, electromotive force (emf) and internal resistance of cells, and **Kirchhoff's laws** (junction and loop rules) are applied for analyzing complex electric circuits. The **heating effect of current** ($\textsf{H} = \textsf{I}^2\textsf{Rt}$) and **electric power** ($\textsf{P} = \textsf{VI}$) are also covered, quantifying energy transfer in circuits.
4. Moving Charges And Magnetism
This chapter establishes the crucial relationship between electricity and magnetism: **moving electric charges produce magnetic fields**. it introduces the magnetic field ($\vec{\textsf{B}}$) and the **Lorentz force** ($\vec{\textsf{F}} = \textsf{q}(\vec{\textsf{E}} + \vec{\textsf{v}} \times \vec{\textsf{B}})$) acting on a charge moving in electric and magnetic fields. Methods for calculating magnetic fields due to current distributions are introduced using the **Biot-Savart Law** and **Ampere's Circuital Law** (for straight wires, loops, solenoids). The magnetic force on a current-carrying conductor, torque on a current loop, and the working principle of a **moving coil galvanometer** are explained, foundational to electromagnetism.
5. Magnetism And Matter
This chapter explores the magnetic properties of different materials and **Earth's magnetism**. It discusses magnetic field lines, magnetic dipole moment, and the magnetic field produced by a bar magnet. **Earth's magnetic field** and its elements (magnetic declination, dip, horizontal intensity) are introduced. Different categories of **magnetic materials** – **diamagnetic**, **paramagnetic**, and **ferromagnetic** – are explained based on their behavior in external magnetic fields, relating macroscopic properties to microscopic structure and **Curie's Law**. The chapter also touches upon permanent magnets and electromagnets, highlighting how materials are chosen for specific magnetic applications.
6. Electromagnetic Induction
This chapter introduces the phenomenon of **electromagnetic induction**, where a changing magnetic field or magnetic flux induces an electromotive force (emf) and current in a circuit. **Faraday's laws of induction** quantify the magnitude of the induced emf, while **Lenz's Law** determines its direction, stating that the induced current opposes the cause producing it. Concepts like **motional emf** (induced by movement in a magnetic field) and **self and mutual inductance** are explained. The chapter covers **eddy currents** and their applications/disadvantages, and discusses the working principle of the **AC generator**, a device that converts mechanical energy into electrical energy based on electromagnetic induction.
7. Alternating Current
This chapter focuses on **Alternating Current (AC)** and voltage, which vary periodically in magnitude and direction, unlike direct current (DC). It introduces concepts like instantaneous, peak, and RMS values of AC. Analysis of AC circuits containing resistors (R), inductors (L), and capacitors (C), individually and in series (LCR circuit), is done using phasor diagrams and impedance. Concepts like reactance, impedance, phase difference, **resonance** (in LCR circuits), Q-factor, and **power in AC circuits** are discussed. The working principle of the **transformer**, a crucial device for stepping up or down AC voltages, vital for power transmission in India.
8. Electromagnetic Waves
This chapter introduces **electromagnetic waves**, non-mechanical waves that propagate through vacuum and media at the speed of light ($\textsf{c}$). They consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation, as described by **Maxwell's equations**. The chapter discusses their characteristics, including energy and momentum. The entire **electromagnetic spectrum**, from radio waves to gamma rays, is presented, highlighting the properties and diverse applications of different parts of the spectrum (communication, medical imaging, heating, etc.), showcasing the unified nature of light and electromagnetism.
9. Ray Optics And Optical Instruments
This chapter treats light as rays propagating in straight lines, forming the basis of **ray optics** or geometric optics. It covers **reflection** from plane and spherical mirrors (laws of reflection, mirror formula $\frac{1}{\textsf{v}} + \frac{1}{\textsf{u}} = \frac{1}{\textsf{f}}$) and **refraction** as light passes between media (laws of refraction, **Snell's Law** $\textsf{n}_1 \sin \theta_1 = \textsf{n}_2 \sin \theta_2$, refraction through prism and lens). **Total internal reflection** and its applications are discussed. Image formation by lenses (lens formula $\frac{1}{\textsf{v}} - \frac{1}{\textsf{u}} = \frac{1}{\textsf{f}}$, power of a lens) and the working of optical instruments like the **human eye**, microscope, and telescope are covered.
10. Wave Optics
Moving beyond the ray model, this chapter explains optical phenomena using the **wave nature of light**. **Huygens' principle** is introduced to describe wave propagation and explain reflection/refraction. **Interference**, the superposition of waves resulting in constructive or destructive effects, is detailed, with **Young's double-slit experiment** as a key demonstration of **wave interference** (fringe width $\beta = \frac{\lambda\textsf{D}}{\textsf{d}}$). **Diffraction**, the bending of waves around obstacles or through slits, is discussed (single slit diffraction). The chapter also introduces **polarization**, a property specific to transverse waves, and its methods and applications.
11. Dual Nature Of Radiation And Matter
This revolutionary chapter explores the concept of **wave-particle duality**, stating that both light (**radiation**) and **matter** (like electrons) exhibit properties of waves and particles. It discusses the **photoelectric effect**, which supports the particle nature of light (photons) and is explained by **Einstein's photoelectric equation** ($\textsf{h}\nu = \phi_0 + \textsf{KE}_\text{max}$). **De Broglie's hypothesis** ($\lambda = \frac{\textsf{h}}{\textsf{p}}$) proposes the wave nature of matter particles, experimentally confirmed by Davisson and Germer. This duality is a fundamental concept in quantum mechanics, fundamentally changing our view of the microscopic world.
12. Atoms
This chapter delves into the structure of the atom, focusing primarily on the **Bohr model** for the hydrogen atom. It discusses Rutherford's alpha scattering experiment leading to the nuclear model and its limitations. **Bohr's postulates** regarding quantized energy levels and angular momentum are explained. The chapter uses Bohr's theory to calculate the energy levels, radii, and velocities of electrons in hydrogen. The origin of atomic spectra, specifically the different **spectral series** (Lyman, Balmer, Paschen, Brackett, Pfund) of hydrogen, is explained based on electron transitions between energy levels, demonstrating the quantized nature of atomic energy.
13. Nuclei
This chapter focuses on the **atomic nucleus**, its composition (protons and neutrons), size, density, and mass. Concepts like **mass defect** ($\Delta \textsf{m}$) and **binding energy** ($\textsf{E}_\text{b} = \Delta \textsf{mc}^2$) are introduced to explain nuclear stability. **Radioactivity** – the spontaneous decay of unstable nuclei ($\alpha$, $\beta$, $\gamma$ emissions) – is discussed, along with the laws of radioactive decay ($N = N_0 e^{-\lambda t}$) and the concept of **half-life** ($T_{1/2}$). **Nuclear energy** released through **fission** (splitting heavy nuclei, used in nuclear reactors) and **fusion** (combining light nuclei, powering the sun) is explained, highlighting their immense energy potential and applications.
14. Semiconductor Electronics: Materials, Devices And Simple Circuits
This chapter introduces **semiconductors**, materials with conductivity between conductors and insulators, forming the basis of modern electronic devices. It discusses energy bands in solids and classifies materials based on conductivity. **Intrinsic and extrinsic semiconductors** (p-type and n-type), created by doping, are explained. The formation and properties of a **p-n junction** are detailed, including forward and reverse biasing and the depletion region. Basic **semiconductor devices** like the **p-n junction diode** (used as a rectifier to convert AC to DC) and the **transistor** (as an amplifier or switch) are covered. The chapter also introduces **logic gates** (AND, OR, NOT) as fundamental building blocks of digital circuits, crucial for the digital revolution impacting India and the world.