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Chapter 6 – Modern Physics

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:


Modern physics is a subset of physics that deals with post-Newtonian concepts in the field of physics. It is focused on the two great breakthroughs of the 20th century—relativity and quantum mechanics.

Modern physics also requires an advanced explanation of existence by modern ideas that are separate from classical descriptions, including aspects of quantum mechanics and Einsteinian relativity. For example, quantum effects usually include distances relative to atoms. On the other hand, relativistic effects usually entail velocity relative to the speed of light.

The mechanism by which free electrons are released from the surface of metal while additional heat energy is used is known as thermionic emission. Thermionic emission happens in metals that are heated to a high temperature. In other words, it happens when a sufficient amount of additional energy in the form of heat is provided to free electrons in metals.

As a negligible amount of heat energy is given to the metal, the valence electrons accumulate sufficient energy and sever the bond with the parent atom. The valence electron, which splits the bond with the parent atom, gets freed. This electron, which splits the bond with the parent atom, is considered a free electron.

Due to nuclear instability, the nucleus of the atom exhibits the phenomenon of radioactivity. Energy is lost due to radiation released by the unstable nucleus of the atom. Two forces, namely the electrostatic repulsion force and the strong attraction forces of the nucleus, hold the nucleus together. These two powers are thought to be highly powerful in the natural world. The risk of witnessing instability increases as the nucleus’s size increases since the nucleus’ mass becomes even denser. That is why the atoms in plutonium, uranium are highly unstable and undergo the phenomena of radioactivity.

Nuclear structure studies the characteristics of the nucleus in isolation, such as nuclear mass, characteristic energy levels and modes of radioactive decay.

The overall number of protons in the atom’s nucleus gives us the atomic number of the atom. It is represented by the letter ‘Z’. The atoms of a given element have the same number of protons and thus the same atomic number. Atoms with different components have different atomic numbers. For example, all carbon atoms have an atomic number of 6, and all oxygen atoms have 8 protons in their nucleus.

The sum of protons and neutrons together givesnucleus’s us the mass of the atom. It is represented by the letter ‘A’. As both protons and neutrons are found in the nucleus of the atom, they are called nucleons. For example, the carbon atom has 6 protons and 6 neutrons, and therefore, its mass number is 12. Although the number of protons remains the same in all the atoms of the element, the number of neutrons can differ. As a result, atoms of the same element can have different mass numbers, and these are called isotopes. The electron’s weight is almost negligible. Thus, the atomic mass of an atom is exactly the same as its mass number.

Radioactivity is exhibited naturally by certain kinds of radiation-emitting matter and subatomic particles. It is, in fact, the attribute of a single atomic nucleus.

An unstable nucleus will decompose spontaneously or decay into a more stable state, but only in a few particular ways by releasing certain particles or certain sources of electromagnetic radiation. Radioactive decay is the property of a number of naturally occurring elements and chemically formed isotopes of the elements. The rate at which the radioactive element decays is calculated in terms of its half-life—the time taken for one-half of some given amount of the isotope to decay.

Some uses of radioactivity are listed below. These properties depict the phenomenon of radioactivity and changes in the nucleus as well.

  • Americium-241 is an alpha emitter used by domestic smoke alarms in the United States.
  • The alpha particles produced by the Americium sample ionise the air in the smoke detector chamber, contributing to a slight current in the chamber.
  • When smoke reaches the chamber, a decrease in the current causes the alarm to go off. While Alpha particles have a very short range, they are lethal when in near contact with each other.
  • Alpha emitters, when ingested, come in direct contact with tissue and are lethal in certain situations and are often used in assassination attempts via radiation poisoning.

This chapter shed light on the concept of modern physics, where we learnt about some concepts like radioactivity, thermionic emission, nuclear structure, atomic number and mass number.

  1. tate the difference between an isotope and a radioactive isotope?
    Isotopes are atoms of the same element with different neutron numbers but the same number of protons and electrons. Radioactive (unstable) isotopes have nuclei that decay randomly over time to form other isotopes.
  2. What does the half-life of an isotope mean?
    Half the life of an isotope is the total time it takes for half of the atoms to decay.
  3. Give some uses of radioactivity.
    Used for indoor smoke detectors.
    B. Used to sterilise surgical devices.
    C. Used to detect and cure illness.
    D. Used to generate electrical power.
  4. Who found the atomic number?
    The number of protons (positive charges) in an atom’s nucleus is determined by its atomic number. Henry Gwyn-Jefferies Moseley first introduced the concept.
  5. Define mass number.
    The total number of protons and neutrons in the nucleus of the atom. For example, nitrogen has seven protons in its nucleus and seven neutrons to provide 14 masses.

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High School Physics

  • Alternating Current
  • Atoms
  • Communication Systems
  • Current Electricity
  • Dual nature of Radiation and Matter
  • Electric Charges and Fields
  • Electricity
  • Electromagnetic Induction
  • Electromagnetic Waves
  • Electron Beams and Radioactivity
  • Electrons and Photons
  • Electrostatic Potential and Capacitance
  • Fluid Pressure
  • Force and Acceleration
  • Force And Laws Of Motion
  • Gravitation
  • Internal Energy
  • Kinetic Theory
  • Law of motion
  • Light – Reflection And Refraction
  • Magnetic Effects Of Electric Current
  • Magnetism and Matter
  • Management Of Natural Resources
  • Mechanical properties of Fluids
  • Mechanical properties of Solids
  • Motion
  • Motion in a plane
  • Motion in a straight line
  • Moving Charges and Magnetism
  • Nuclear Energy
  • Nuclei
  • Oscillations
  • Our Environment
  • Paths of Heat
  • Physical world
  • Ray optics and optical instruments
  • Semiconductor Devices
  • Semiconductor Electronics: Materials, Devices and Simple Circuits
  • Simple Machines
  • Sound
  • Sources Of Energy
  • Specific and Latent Heats
  • Spherical Mirrors
  • Static Electricity
  • Systems of Particles and Rotational motion
  • Thermal properties of matter
  • Thermodynamics
  • Units and Measurement
  • Vectors, Scalar Quantities and Elementary Calculus
  • Wave Optics
  • Waves
  • Work, Power and Energy

High School Chemistry

  • Acids, Bases and Salts
  • Alcohols, Phenols and Ethers
  • Aldehydes, Ketones and Carboxylic Acids
  • Aliphatic and Aromatic Hydrocarbons
  • Alkyl and Aryl Halides
  • Amines
  • Analytical Chemistry 
  • Atomic Structure
  • Atoms And Molecules
  • Basic concepts of Chemistry
  • Biomolecules
  • Carbon And Its Compounds
  • Carboxylic acids and Acid Derivatives
  • Chemical Bonding and Molecular Structures
  • Chemical Energetics
  • Chemical Equilibria
  • Chemical Kinetics
  • Chemical Reactions And Equations
  • Chemical Reactions and Their Mechanisms
  • Chemistry in Everyday Life
  • Chemistry of p-Block elements
  • Chemistry of Transition and Inner Transition
  • Classification of Elements
  • Coordination Compounds
  • Cyanide, Isocyanide, Nitro compounds and Amines
  • Electrochemistry
  • Electrolysis
  • Elements, Compounds and Mixtures
  • Environmental Chemistry
  • Equilibrium
  • Ethers and Carbonyl compounds
  • Haloalkanes and Haloarenes
  • Hydrocarbons
  • Hydrogen
  • Ideal solutions
  • Introduction to Organic Chemistry
  • Ionic equilibria
  • Matter
  • Matter Around Us
  • Matter In Our Surroundings
  • Metallurgy
  • Metals And Non-Metals
  • Mole Concept and Stoichiometry
  • Natural Resources
  • Organic Chemistry – Basic Principles
  • Periodic Classification of Elements
  • Physical and Chemical Changes
  • Physical and Chemical Properties of Water
  • Polymers
  • Preparation, Properties and Uses of Compounds
  • Principles and Processes of Isolation of Elements
  • Redox Reactions
  • Relative Molecular Mass and Mole
  • States of Matter
  • Structure Of The Atom
  • Study of Compounds
  • Study of Gas Laws
  • Study of Representative Elements
  • Surface Chemistry
  • The d-block and f-block elements
  • The Gaseous State
  • The p-Block Elements
  • The Periodic Table
  • The s-Block Elements
  • The Solid State
  • Thermodynamics

High School Biology

  • Absorption and Movement of Water in Plants
  • Adolescent Issues
  • Anatomy of Flowering Plants
  • Animal Kingdom
  • Bacteria and Fungi-Friends and Foe
  • Biodiversity and Conservation
  • Biofertilizers
  • Biological Classification
  • Biomedical Engineering
  • Biomolecules
  • Biotechnology and its Applications
  • Biotic Community
  • Body Fluids and Circulation
  • Breathing and Exchange of Gases
  • Cell – Unit of Life
  • Cell Cycle and Cell Division
  • Cell Division and Structure of Chromosomes
  • Cell Reproduction
  • Cellular Respiration
  • Chemical Coordination and Integration
  • Circulation
  • Control And Coordination
  • Crop Improvement
  • Digestion and Absorption
  • Diversity In Living Organisms
  • Ecosystem
  • Environmental Issues
  • Excretory Products and their Elimination
  • Flowering Plants
  • Genes and Chromosomes
  • Health and Diseases
  • Health and Its Significance
  • Heredity And Evolution
  • Heredity and Variation
  • How Do Organisms Reproduce?
  • Human Diseases
  • Human Eye And Colourful World
  • Human Health and Disease
  • Human Population
  • Human Reproduction
  • Hygiene
  • Improvement In Food Resources
  • Integumentary System- Skin
  • Kingdom Fungi
  • Kingdom Monera
  • Kingdom Protista
  • Life Processes
  • Locomotion and Movement
  • Microbes in Human Welfare
  • Mineral Nutrition
  • Molecular Basis of Inheritance
  • Morphology of Flowering Plants
  • Neural Control And Coordination
  • Nutrition in Human Beings
  • Organism and Population
  • Photosynthesis
  • Photosynthesis in Higher Plants
  • Plant Growth and Development
  • Plant Kingdom
  • Pollination and Fertilization
  • Pollution; Sources and its effects
  • Principles of Inheritance and Variation
  • Reproduction and Development in Angiosperms
  • Reproduction in Organisms
  • Reproductive Health
  • Respiration in Human Beings
  • Respiration in Plants
  • Respiratory System
  • Sexual Reproduction in Flowering Plants
  • Strategies for Enhancement in Food Production
  • Structural Organisation in Animals
  • Structural Organisation of the Cell
  • The Endocrine System
  • The Fundamental Unit Of Life
  • The Living World
  • The Nervous System and Sense Organs
  • Tissues
  • Transpiration
  • Transport in Plants

High School Math

  • Algebra – Arithmatic Progressions
  • Algebra – Complex Numbers and Quadratic Equations
  • Algebra – Linear Inequalities
  • Algebra – Pair of Linear Equations in Two Variables
  • Algebra – Polynomials
  • Algebra – Principle of Mathematical Induction
  • Algebra – Quadratic Equations
  • Binomial Theorem
  • Calculus – Applications of Derivatives
  • Calculus – Applications of the Integrals
  • Calculus – Continuity and Differentiability
  • Calculus – Differential Equations
  • Calculus – Integrals
  • Geometry – Area
  • Geometry – Circles
  • Geometry – Conic Sections
  • Geometry – Constructions
  • Geometry – Introduction to Euclid’s Geometry
  • Geometry – Three-dimensional Geometry
  • Geometry – Lines and Angles
  • Geometry – Quadrilaterals
  • Geometry – Straight Lines
  • Geometry – Triangles
  • Linear Programming
  • Matrices and Determinants
  • Mensuration – Areas
  • Mensuration – Surface Areas and Volumes
  • Number Systems
  • Number Systems – Real Numbers
  • Permutations and Combinations
  • Probability
  • Sequence and Series
  • Sets and Functions
  • Statistics 
  • Trignometry – Height and Distance
  • Trignometry – Identities
  • Trignometry – Introduction

Middle School Science

  • Acids, Bases And Salts
  • Air and Its Constituents
  • Basic Biology
  • Body Movements
  • Carbon and Its Compounds
  • Cell – Structure And Functions
  • Changes Around Us
  • Chemical Effects Of Electric Current
  • Chemistry in Your Life
  • Coal And Petroleum
  • Combustion And Flame
  • Components Of Food
  • Conservation Of Plants And Animals
  • Crop Production And Management
  • Electric Current And Its Effects
  • Electricity And Circuits
  • Elements and Compounds
  • Fibre To Fabric
  • Food production and management
  • Force And Pressure
  • Forests: Our Lifeline
  • Friction
  • Fun With Magnets
  • Garbage In, Garbage Out
  • Getting To Know Plants
  • Health and Hygiene
  • Heat
  • Hydrogen
  • Life Processes: Nutrition in Animals and Plants
  • Light, Shadows And Reflections
  • Materials: Metals And Non-Metals
  • Matter and Its States
  • Metals and Non-metals
  • Micro Organisms: Friend And Foe
  • Motion And Measurement Of Distances
  • Motion And Time
  • Nutrition In Animals
  • Nutrition In Plants
  • Organization in Living Things
  • Our Environment
  • Physical And Chemical Changes
  • Pollution and conservation
  • Pollution Of Air And Water
  • Reaching The Age Of Adolescence
  • Reproduction In Animals
  • Reproduction In Plants
  • Respiration In Organisms
  • Rocks and Minerals
  • Separation Of Substances
  • Simple Machines
  • Soil
  • Some Natural Phenomena
  • Sorting Materials Into Groups
  • Sound
  • Stars And The Solar System
  • Structure of Atom
  • Synthetic Fibers And Plastics
  • The Living Organisms And Their Surroundings
  • Transfer of Heat
  • Transformation of Substances
  • Transportation In Animals And Plants
  • Universe
  • Waste-water Story
  • Water: A Precious Resource
  • Weather, Climate And Adaptations Of Animals To Climate
  • Winds, Storms And Cyclones

Middle School Math

  • Addition
  • Area and Its Boundary
  • Boxes and Sketches
  • Data Handling
  • Fun With Numbers
  • Heavy and Light
  • How Many
  • Long And Short
  • Mapping
  • Measurement
  • Money
  • Multiplication and Factors
  • Multiply and Divide
  • Numbers
  • Parts and Wholes
  • Pattern Recognition
  • Patterns
  • Play With Patterns
  • Rupees And Paise
  • Shapes And Angles
  • Shapes And Designs
  • Shapes and Space
  • Similarity
  • Smart Charts
  • Squares
  • Subtraction
  • Tables And Shares
  • Tenths and Hundredths
  • Time
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