# Chapter 8 – Electromagnetic Waves

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

Introduction

We have studied that a changing magnetic field creates an electric field. But the opposite is also true. An electric current or a time-varying electric field generates a magnetic field. This was suggested and proved by James Clerk Maxwell, who formulated a set of equations known as Maxwell’s equations. One of the most important predictions from these equations was the existence of electromagnetic waves. Electromagnetic waves are synchronised time-varying electric and magnetic fields that propagate in space. The speed of electromagnetic waves in free space is very close to the speed of light (3 x 108 m/s), which led to the conclusion that even light is an electromagnetic wave.

#### Applications of electromagnetic waves

All wireless communications, FM radio, X-ray machines, microwave oven etc. work using these waves.

#### Displacement Current

Displacement current is the current formed due to a changing electric field, and conduction current is the current carried by conductors due to flow of charges.

The Ampere-Maxwell law states that the total current passing through any surface of which the closed-loop is the perimeter is the sum of the conduction current and the displacement current. It is represented as

∮ Magnetic field * dl(very small length) = μ0 ic + μ0 ε0 dΦEdt

where B is the magnetic field, ic is the conduction current, and ΦE is the electric flux.

This proves that the laws of electricity and magnetism are more symmetrical. Faraday’s law of electromagnetic induction can be rephrased as a magnetic field changing with time gives rise to an electric field. Hence, time-dependent electric and magnetic fields give rise to each other.

#### Electromagnetic Waves

Sources of Electromagnetic Waves:

Stationary charges or steady currents cannot create electromagnetic waves; they only create electrostatic fields and magnetic fields, respectively. Only accelerated charges can create these waves. A charge oscillating with some frequency produces an oscillating electric field in space. This produces an oscillating magnetic field, which, in turn, creates an oscillating electric field and so on. Thus, the oscillating electric and magnetic fields are regenerating each other, and this electromagnetic wave propagates in space. The frequency of this wave is equal to the frequency of oscillation of the charge.

Nature of Electromagnetic Waves:

The electric and magnetic fields in these waves are perpendicular to each other as well as to the direction of propagation. In free space or vacuum, these waves are self-sustaining oscillations of their electric and magnetic fields. And there is no material medium involved in the vibrations of these fields. The velocity of these waves in free space or vacuum is constant. Electromagnetic waves are polarised and can be diffracted and refracted.

Total Energy of an Electromagnetic Wave:

Electromagnetic waves also carry energy and momentum like other waves when they move through space. The energy is shared through their magnetic and electric fields. When these waves strike the surface, along with total energy, the pressure is also exerted on it.

Electromagnetic Spectrum:

When electromagnetic waves were predicted to exist, the only known electromagnetic waves were light waves. Today we are aware of  X-rays, gamma rays, radio waves, microwaves, ultraviolet and infrared waves apart from light waves. The electromagnetic spectrum is the classification of electromagnetic waves based on frequency.

• Radio Waves: These waves are created by the accelerated motion of charges in wires and have applications in radio and television communication systems. The frequency range is from 500 kHz to 1000 MHz. TV waves range from 54 MHz to 890 MHz, while FM radio band range is from 88 MHz to 108 MHz. In contrast, radiowaves of the ultrahigh-frequency (UHF) band is used in cellular phones to transmit voice communication.
• Microwaves: These are short-wavelength radio waves that are created by special vacuum tubes and have frequencies in GHz range. These waves are used for radar systems in aircraft navigation and for speed guns used to time the speed of fastballs in games and of automobiles. Another popular application is for domestic use as microwave ovens to heat and cook food.
• Infrared Waves: This band lies next to the low-frequency or long-wavelength end of the visible spectrum, and hot bodies and molecules produce them. This radiation also helps in maintaining the earth’s temperature through the greenhouse effect. Infrared detectors are used in Earth satellites and electronic devices such as remote switches for TV sets, video recorders, etc.
• Visible Rays: These waves can be detected by the human eye and are within the frequency range from 4 x 104 Hz to 7 x 1014 Hz. Visible light reflected on surfaces makes various objects visible to us.
• Ultraviolet Rays: Special lamps and very hot bodies produce ultraviolet (UV) radiation. The sun is an important example of this. These rays cover the wavelength range from 4 x 10-7 m to 6 x 10-10 m. Excessive exposure to UV light is harmful to human beings, and thus the ozone layer in the atmosphere plays a vital role in absorbing most of it.
• X-Rays: These rays lie in the wavelength range from 10-8 m to 10-13 m and have popular applications in the medical field. It is used as a diagnostic tool and as a treatment for cancer. Overexposure can damage or destroy tissues and organisms, so its use should be monitored.
• Gamma Rays: They lie in the wavelength range from 10-10 m to about 10-14 m. These are high-frequency waves produced in nuclear reactions and by radioactive material. These rays are used in medicine to destroy cancer cells.

Our day-to-day life depends on using the internet on our phones and laptops, making calls, watching TV etc. This is only possible because of electromagnetic waves, which forms the foundation of modern-day technology. Maxwell’s equations were also used to form the basis of Electromagnetic wave equation, Maxwell’s wave equations and Helmholtz wave equation that have many other applications. Check out this concept visualized further more details in on the MSVgo app.

### 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
• 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
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• Mole Concept and Stoichiometry
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• Periodic Classification of Elements
• Physical and Chemical Changes
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• Preparation, Properties and Uses of Compounds
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• 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
• 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
• Binomial Theorem
• Calculus – Applications of Derivatives
• Calculus – Applications of the Integrals
• Calculus – Continuity and Differentiability
• Calculus – Differential Equations
• Calculus – Integrals
• Geometry – Area
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• Geometry – Introduction to Euclid’s Geometry
• Geometry – Three-dimensional Geometry
• Geometry – Lines and Angles
• 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
• 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
• 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

• 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