# Chapter 4 – Light Energy

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

Introduction

Light is an energy that plays an important role in our lives. Light is important to be studied because if we did not have like we could not interpret the world around us. The natural source of light is the sun, and there are also other sources that emit light like candles, electric bulbs, torch, etc.

People took some time to realise that the speed of light is measurable and finite. The presently accepted value of the speed of light in a vacuum is c = 3 x 108 m/s. Did you know? The speed of light in a vacuum is the highest speed attainable in nature.

#### Light Energy

When the vibrations of electrically charged particles produce energy it is called light energy. Light energy is Electromagnetic radiation. The only form of energy that is visible to the human eye is the light energy. For example: Have you ever noticed the light in the oven used to cook the food? It is a form of light energy.

#### Use of light energy

Light energy is used for various reasons, a few of them are as follows:

• Growth of the human body
• Food formation
• Sight and vision
• Regulation of  physiology
• Drying and evaporation
• Heat and temperature
• For speed regulation
•  Signalling system

#### Interesting fact

A human eye has the ability to distinguish between 6000 different shades of a particular colour and it is possible only because of light. Light has a different electromagnetic spectrum, and each spectrum has seven colours, namely  violet, Indigo, blue, green, yellow, orange, red (VIBGYOR). When light falls on an object, the object absorbs light of some wavelength whereas reflects others. To understand this better, let us now learn what reflection of light is.

#### Reflection

The process in which the light rays are sent back after falling on a surface of an object is called reflection of light. The easiest example of reflection would be the image you see of yourself in the mirror or the smooth pool of water.

Let us now understand the different terms related to reflection:

1. Normal plane: A normal plane is a plane that contains the normal vector of the surface at a particular point.
2. Point of incidence: The point on the surface on which the incident ray strikes the surface is called the point of incidence.
3. Normal: The line perpendicular to the point of incidence at the surface is the normal.
4. Angle of incidence: It is the angle between the normal and the incident ray on a surface.
5. Angle of reflection: It is the angle between the reflected ray and the normal that is drawn at the point of incidence on the reflecting surface.

#### Law of reflection

The law of reflection is defined as “The principal when the light rays fall on the smooth surface,  the angle of reflection is equal to the angle of incidence. Also, the normal to the surface, the incident ray, and the reflected ray, all lie in the same plane.”

#### Plane Mirror

The only type of mirror for which a real object always produces an image that is erect, virtual, and of the same size as the object is called the plane mirror.

Virtual and real image:

Virtual Image: An image formed when the outgoing rays from an object move apart (diverge) it is called a virtual image. a virtual image is formed on a plane mirror when positioned behind the mirror.

Real Image: An image formed by the actual intersection of rays of light is called a real image.

The rays of light actually meet in real image after reflection while in a virtual image it appears to meet but it does not actually meet. We can obtain a real image on the screen but a virtual image cannot be.

Lateral Inversion

The phenomenon in which the left appears to be right and vice versa is called lateral inversion.  This happens due to the direction that light follows when it strikes a reflecting surface, generally on a  mirror. In a plane mirror,  the image is as far behind the mirror as the object is in front of it, and that the front of the image and the front of the object face each other, and hence lateral inversion occurs. For example, the letter “d” when laterally inverted would look like the letter “b” (more or less).

Uses of a plane mirror

• Plane mirrors are used as looking glass.
• Solar cookers.
• In Kaleidoscope.
• In scientific instruments.

#### Conclusion

Light is a form of energy that plays a vital role in our lives. Light from an object can move through space and it reaches the human eye which enables us to see the things around, be it seeing the screen of the computer or your face in the mirror. We have learnt all the important concepts of light energy.

#### FAQs

1. What are the different types of light energy?
A:  UV light, Visible light, X-rays, Infrared light.
2. Is light energy kinetic energy?
A: Yes, light energy is kinetic energy. The speed of light is measured to be approximately equal to 3 x 108 m/s.
3. What kind of image does a plane mirror form?
A:  A plane mirror always forms a virtual image (behind the mirror).
4. What are the characteristics of a plane mirror?
A:  Characteristics of the plane mirror are as follows:
a). It always forms a virtual and erect image.
b). The image size is always equal to the size of the object.
c). The image that is formed is equally behind the mirror as the object is in front of it.
d). The images are laterally inverted.
5. What is an example of reflection?
A: On the surface of a smooth pool of water,  when the incident light is reflected in an orderly manner such that a clear image of the scenery around the pool is seen in it.

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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
• 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
• 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
• Geometry – Circles
• Geometry – Conic Sections
• Geometry – Constructions
• 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