# Chapter 6 – Light

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

Introduction

Light is a form of energy that causes a sensation of vision in the eyes and allows us to see things. Have you ever wondered how we can see various beautiful objects around us?

You must have studied about eyes in chapter ‘Human body,’ but do you know what creates a vision in our eyes? Yes, it is light.

ICSE Class 9th Physics chapter ‘Light’ covers all the vital topics related to light, like a reflection of light and spherical mirrors. It is also used in successive chapters of class 9th physics, so a clear understanding of light will help better understand other scientific concepts.

Chapter ‘Light’ covers the following topics:

• Introduction to light
• Reflection of light
• Laws of reflection
• Uses of concave and convex mirrors
• Properties of mirrors
• Images formed by a pair of parallel and perpendicular plane mirrors
• Characteristics of images formed in a pair of mirrors
• Location of images formed in mirrors

#### Introduction to Light

As already stated, light is a form of energy that causes a sensation of vision in the eyes and allows us to see things. The study of light in physics is known as Optics, and it is an essential concept for advanced physics. Light causes a sensation of vision in the eyes. For example, light from a torch and motorcycles causes a sensation of sight in the eyes. Light always travels in a straight line unless the direction of light is changed using reflection and refraction concepts.

#### Reflection of Light

Reflection is a phenomenon when the light bounces back to the emitting medium after striking a surface. Different surfaces react differently when the light strikes:

• Opaque surface: In the case of opaque surfaces, the whole light beam gets reflected. So, opaque surfaces help in the reflection process.
• Translucent surface: In fine characters, a portion of the light beam is reflected while the rest is transmitted through the surface. So, translucent surfaces partially help in the reflection process.
• Transparent surface: In the case of transparent surfaces, the whole light beam gets transmitted through the surface, and reflection does not take place. So, transparent surfaces do not help in the reflection process of light.

#### Laws of Reflection

• This law states that when a light beam is reflected upon a smooth opaque surface, the angle formed by the reflected ray is equal to the angle formed by the incident ray with respect to the perpendicular formed from the point of contact on the surface.
• It also states that the incidence ray, the perpendicular, and the reflected ray lie in the surface’s same plane.

Formula: Angle of reflection = Angle of incidence

#### Properties of Mirror Images formed by a Pair of Parallel And Perpendicular Plane Mirrors

Following are the properties of images formed by the mirrors:

• The image formed is virtually erect.
• The size of the source and the image formed is precisely the same.
• The distance between the images formed and the mirror is the same as the distance between the source and the mirror.
• The image formed in the mirror is inverted.

#### Types of Mirrors

There are two broad types of mirrors:

• Plane mirrors
• Spherical mirrors
• Concave mirror
• Convex mirror

#### Uses of Spherical Mirrors

Spherical mirrors are of 2 types:

• Convex mirror
• Concave mirror

Concave Mirror and Uses
Spherical mirrors with a reflected surface curved inwards are known as concave mirrors. They are also referred to as converging mirrors.
Uses of Concave Mirror:

• It is used as shaving mirrors in salons.
• Dentists use it to focus light on teeth by diagnosis.
• They are used as headlights of cars to create a powerful source of light.
• It is used in satellite dishes to concentrate weaker signals together.

Convex Mirror and Uses
Spherical mirrors with a reflected surface curved outwards are known as concave mirrors. They are also referred to as diverging mirrors.
Uses of Convex Mirror:

• Convex mirrors are used as rear view mirrors in cars, which helps drivers look at the vehicles coming from behind.
• It is even used as security mirrors in ATMs, allowing the customer to see their image behind them.

#### Characteristics of Images Formed in a Pair of Mirrors

The object’s image is formed in both the mirrors as the image in the first mirror becomes the object for the second mirror. The following are the characteristics of images included in a pair of mirrors:

• All the images are virtually erect.
• The size of the source object and the images formed are the same.
• The distance between the images formed and the mirror is the same as the distance between the source and the mirror.
• The image formed in mirror 1 is inverted, while the image formed in mirror 2 is similar to the object.

#### Location of Images Formed in the Plane Mirror

According to the law of reflection, the angle of reflection is equal to the angle of incidence, which means that the distance between the mirrors and the object is the same as the distance between the mirrors and the image formed. Using this concept, the image’s location created in the plane mirror can be calculated as the distance is the same but in opposite directions.

#### Images Formed By a Pair of Parallel and Perpendicular Plane Mirrors

A total of three images are formed when an object is placed between two perpendicular plane mirrors.

When an object is placed between a pair of parallel plane mirrors, an infinite number of images are formed.

#### Conclusion

Light is a straight line electromagnetic radiation of any wavelength visible to human eyes that can be deviated using reflection and refraction concepts. The chapter ‘Light’ is not only an essential topic for class 9th physics, but it is also a necessary concept for advanced physics. This chapter’s thorough knowledge will smoothen your journey through the upcoming physics and science chapters.

#### FAQs

1. What is the angle of reflection?
The angle of reflection is the angle formed between the reflected ray and the perpendicular at the reflection point.
2. What is the angle of incidence?
The angle of incidence is the angle formed between the incident ray and the perpendicular at the reflection point.
3. How many images are formed when an object is placed between a pair of parallel mirrors?
When an object is placed between a pair of parallel plane mirrors, an infinite number of images are formed.
4. How many images are formed when an object is placed between mutually perpendicular mirrors?
When an object is placed between a pair of parallel plane mirrors, an infinite number of images are formed.

‘Light’ is an essential chapter of physics. So, the visual representation of this chapter is necessary. MSVgo offers a large base of learning videos and interactive learning methods like quizzes, interactive games, and more. MSVgo is a smartphone application available on both android and IOS that explains every concept with interactive visual representations. Check out the MSVgo application to know more and get access to more than 6000 science and mathematics videos.

### 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