# Chapter 15 – Light

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

Introduction

What happens when you enter a dark room? Is anything visible to you? Clearly, the answer is—no. However, when you light up the room, you can see the things in it.

So, what makes these things visible? The answer is light—a form of energy that allows us to see objects. In other words, it stimulates the sense of sight and makes the surrounding things visible to us.

#### Light Travels Along a Straight Line

If you switch on a torch in a dark room, you will see a straight beam of light. Similarly, when you view a candle using a straight pipe, it is visible. What happens when you try to observe a candle using a bent pipe? You cannot see the candle.

From the above instances, we can deduce that light travels along a straight line— this phenomenon is also known as the rectilinear propagation of light. If some object covers the source of light, its path gets blocked.

There are three categories of objects based on their interaction with light.

• Transparent objects – Light can completely pass through them; for example, glass.
• Translucent objects – Light can pass partially through them, for example, vegetable oil.
• Opaque objects – Light cannot pass through them. It is either absorbed or reflected by the object, for example, wood.

#### Reflection of Light

Why do you see the reflection of surrounding structures, like trees, in the water? It happens because the water surface acts as a mirror and changes the direction of light.

When some surfaces like a mirror, water, or other polished surfaces change the direction of light that falls on it, the phenomenon is known as a reflection of light

• An incident ray is a fine beam of light that falls on the reflecting surface.
• A reflected ray is a fine beam of light that is reflected.
• Normal is the perpendicular line on the reflecting surface at the point of incidence.
• The angle of incidence (i) is the angle between the normal and incident ray.
• The angle of reflection (r) is the angle between the normal and the reflected ray.

#### Laws of Reflection

• It states that the reflected, normal, and incident ray are all in the same plane.
• It states that both the angles of reflection and incidence are always equal.

#### Images

It is the point where light rays converge or appear to meet. Images can be of two types:

• A real image is formed when the light rays “actually meet” at some point after reflection. These images are always inverted, and you can view them on screen.
• The virtual image appears when the rays of light only seem to meet after reflection. These images are always erect, and you cannot view them on screen.

#### Plane Mirrors

• The image formed by a plane mirror is of the same size as the object. The distance of a substance and its image from the mirror is the same. It is virtual and erect.
• You can see a reflection on a plane mirror only when you are within its range of visibility.
• If you want to see your whole image, then the mirror should be at least half your height.

#### Right or Left Inversion

What happens when you stand in front of a plane mirror and lift your right hand? You see your image raising its left hand.

It happens because of right or left inversion, i.e., the right side of an object appears as the left in the image formed by a plane mirror. It is also the reason the word “AMBULANCE” is written backwards. When the driver ahead of the ambulance views in his mirror, the words appear in the correct order.

#### Spherical Mirrors

Spherical mirrors have curved reflecting surfaces, and they are made from a hollow sphere. There are two types of spherical mirrors:

• When the sphere’s inner surface reflects, it is called a concave mirror.
• When the sphere’s outer surface reflects, it is called a convex mirror.

#### Playing With Spherical Mirrors

When you see your image using the back of a spoon, it is erect and smaller in size.

But when you see your image on the spoon’s inner side, your image is larger and erect. When you move the spoon’s inner side further away from your face, your image is inverted.

The spoon’s back acts as a convex mirror, and the inner surface as a concave mirror. Therefore, we can conclude that:

• Concave mirrors form a real, magnified, and inverted image when the object is far off. When the material is close to the mirror surface, the image formed is virtual and erect.
• Convex mirrors form erect, virtual, and smaller images.

#### Images Formed By Lenses

A lens is a transparent glass piece bound by two spherical surfaces. There are two types of lenses — concave and convex.

• Convex lens, or converging lens, is thicker in the middle and thin at the edges.
• When the distance between the lens and the object is more, the image formed is real, inverted, and much smaller.
• When you move the object much closer to the lens, the image formed is virtual, erect, and magnified.
• A concave lens or diverging lens is thinner in the middle and thick at the edges.
• The image formed is always erect, virtual, and diminished (much smaller than the object).

#### Sunlight — White or Coloured

You may think that sunlight is white, but it actually comprises seven component colours. An example of this is rainbow formation.

When a sunbeam passes through raindrops,  a band of seven colours in the sky appears after the rain. The seven colours are Violet, Indigo, Blue, Green, Yellow, Orange, and Red, i.e., VIBGYOR.

The spectrum of seven colours can also be observed when light passes through a prism. This is known as dispersion.

#### Conclusion

This chapter deals with new concepts related to light and its properties, such as rectilinear propagation, reflection, and dispersion. We have also learned how light rays are emitted from an object and how they travel in a medium.

#### FAQs

1. What exactly is light?
Light is a form of energy that makes our surroundings visible to us.
2. What are the five main characteristics of light?
• Rectilinear propagation, i.e., light travels along a straight line.
• Reflection — When light strikes a surface, it bounces back.
• When light passes through an object by bending through it, it is called refraction.
• Light is composed of many colours.
• When light splits into a spectrum of seven colours based on their wavelength, it is called dispersion.
3. What is light called?
Light is a form of electromagnetic radiation visible by the human eye.
4. What are the seven properties of light?
Reflection, refraction, interference, diffraction, polarisation, scattering, and dispersion.
5. Why is light so important?
Whatever you can see around is because of light, thereby making it essential for us.

To explore more, download MSVgo – a video-based learning app designed to explain complex concepts through simple and explanatory visualisations.

### 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
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• Light – Reflection And Refraction
• Magnetic Effects Of Electric Current
• Magnetism and Matter
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• Physical world
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• Wave Optics
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### High School Chemistry

• Acids, Bases and Salts
• Alcohols, Phenols and Ethers
• Aldehydes, Ketones and Carboxylic Acids
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### High School Biology

• Absorption and Movement of Water in Plants
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• Diversity In Living Organisms
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• Health and Its Significance
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• How Do Organisms Reproduce?
• Human Diseases
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• Kingdom Fungi
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• Locomotion and Movement
• Microbes in Human Welfare
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• Molecular Basis of Inheritance
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• Neural Control And Coordination
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• Photosynthesis in Higher Plants
• Plant Growth and Development
• Plant Kingdom
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• Pollution; Sources and its effects
• Principles of Inheritance and Variation
• Reproduction and Development in Angiosperms
• Reproduction in Organisms
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• Strategies for Enhancement in Food Production
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• 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
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• Binomial Theorem
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• Permutations and Combinations
• Probability
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• Trignometry – Height and Distance
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### 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
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• 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
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• Reaching The Age Of Adolescence
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• Rocks and Minerals
• Separation Of Substances
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• Sound
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• Structure of Atom
• Synthetic Fibers And Plastics
• The Living Organisms And Their Surroundings
• Transfer of Heat
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• 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