Chapter 16: Light for Class 8

In chapter 16 of Class 8 NCERT Science book, we find the topic of ‘Light’. The chapter explains light, its properties and its uses. It is another enjoyable chapter that is informative as well. In this blog, we will read some of the important notes on Class 8 Light.

Also Read: Class 8 Science

Download the Full Class 8 Light Chapter PDF Here

Laws of Reflection

• The angle of incidence is always equal to the angle of reflection. It is the law of reflection.
• The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane. This is another law of reflection.
• On striking a mirror or any other object light generally is reflected in another direction. The light ray which strikes any surface is called the incident ray. The ray that comes back from the surface after the reflection is known as the reflected ray.
•  The line making an angle of 90º to the line representing the mirror or surface of the object at the point where the incident ray strikes the mirror is known as the normal to the reflecting surface at that point.
• The angle between the normal and the incident ray is called the angle of incidence (∠i). The angle between normal and the reflected ray is known as the angle of reflection (∠r).

Lateral Inversion

The image formed by a mirror where the left of the object appears on the right and the right appears on the left is known as lateral inversion.

Types of Reflection

When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as diffused or irregular reflection. The diffused reflection is caused by the irregularities in the reflecting surface not due to the failure of the Law of reflection.

Reflection from a smooth surface like that of a mirror is called regular reflection. Images are formed by regular reflections.

Light PPT For Class 7 & 8 CBSE from Jay Butani

NCERT Class 8 Maths Syllabus

Types of Objects

Illuminated Objects

The objects which shine in the light of other objects are called illuminated objects.

Luminous Objects

The objects which give their own light such as the sun, fire, flame of a candle and an electric lamp are known as luminous objects.

Color of Sunlight

Sunlight is referred to as white light. It consists of 7 colours. These are the same 7 colours as that of the rainbow. The splitting of light into its colours is known as dispersion of light. Rainbow is a natural phenomenon showing dispersion and if sunlight is dispersed using a prism it shows these 7 colours on dispersion.

Also Read: Science Projects for Class 8

The Human Eye

The eye is roughly structured in a spherical shape. The outer coat of the eye is white. It is tough so that it can protect the interior of the eye from accidents. It also is covered by the eyelid so that it can block out the excess light when needed. The eye has many parts which are described below –

Cornea

Its transparent front part is called cornea

Iris

Behind the cornea is a dark muscular structure called the iris. The size of the pupil is controlled by the iris. The iris controls the amount of light entering the eye.  Iris gives the eye its distinctive colour. For example – blue eyes, green eyes, brown eyes etc.

Pupil

In the iris is a small opening called the Pupil

Retina

The lens focuses light on a layer on the back of the eye called the retina. The retina contains several nerve cells.

Optic Nerve

Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve. There are 2 kinds of cells– cones – which are sensitive to bright light and sense colour. Rods are sensitive to dim light.

Blind Spot

The junction of the optic nerve and the retina has no sensory cells so no vision is possible at that spot. Therefore it is called the blind spot.

Sometimes, particularly in old age eyesight becomes foggy due to the eye lens becoming cloudy. When this happens the person is said to have a cataract. There is a loss of vision but it is possible to treat this defect. The opaque lens is removed and a new artificial lens is inserted through technology. You may also be aware of eye problems like myopia and hypermetropia which are problems in seeing farther objects and the closer ones respectively.

Care of the Eyes

Eyes are very important sense organs and therefore it is necessary that you take proper care of your eyes. Given below are some tips on how to take care of your eyes –

• Have a regular checkup. If there is a problem with your eyes you should go to an eye specialist.
• If advised use suitable spectacles.
• Too little or too much light is bad for the eyes. Insufficient light causes strain in the eyes and headaches. Too much light, like that of the sun, a powerful lamp or a laser torch can injure the retina. Therefore do not look at the sun or a powerful light directly.
• Never rub your eyes. If particles of dust go into your eyes wash them gently with clean water. If there is no improvement go to a doctor.
• Wash your eyes with clean water frequently.
• Always read at the normal distance. Do not read by bringing the book too close to your face or keeping it too far.
• Eat a balanced diet. Lack of vitamin A in food is responsible for many eye troubles like night blindness. One should include food like raw carrots, broccoli and green vegetables (such as spinach) and cod liver oil are rich in vitamin A in the diet. Eggs, milk, curd, cheese, butter and fruits such as papaya and mango are also a rich source of vitamin A.

Visually challenged people can also learn to read and write through a special language and other helpful resources. Braille is the most popular language and resources for visually challenged people. It was invented by Louis Braille who was visually challenged himself and published in 1821. The present system was adopted in 1932. There is Braille code for common languages, mathematics and scientific notation and even many Indian languages can be read using this system.

Class 8 Light NCERT Solutions

Q1. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room?

Answer: When we’re in a dark room, we can’t see what’s around us. We can see the objects outside the room because the light is accessible outside the room and rays of light can reach our eyes after being reflected by the objects.

Q2. Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?

Answer: 

Regular Reflection	Diffused Reflection
All the reflected rays are parallel	The reflected rays are not parallel
It occurs on a smooth and polished surface	2. It appears on the rough surface
Reflected rays are in one direction	3. Reflected rays are scattered in diverse directions

No, diffuse reflection does not mean the failure of the laws of reflection. 

Q3. Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

1. Polished wooden table
2. Chalk powder
3. Cardboard surface 
4. Marble floor with water spread over it
5. Mirror
6. Piece of paper

Answer: 

1. Regular Reflection. This is because the surface is flat and polished.
2. Diffused Reflection. This is because the surface is rough.
3. Diffused Reflection. This is because the surface is rough.
4. Regular Reflection. This is because the surface is flat and polished.
5. Diffused Reflection. This is because the surface is rough. 

Q4. State the laws of reflection. 

Answer: The laws of reflection are: 

• The incident ray, the normal and the reflected ray, all lie in the same plane.
• The angle of incidence is equal to the angle of reflection. 

Q5. Fill in the following blanks: 

1. A person 1 m in front of a plane mirror seems to be _____ m away from his image.
2. If you touch your _____ ear with a right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with _____. 
3. The size of the pupil becomes ______ when you see in dim light. 
4. Night birds have _____ cones than rods in their eyes. 

Answer: (a) 2

(b) Left, Left hand

(c) Larger 

(d) Lesser 

Class 8 Light MCQs

Choose the correct option in the following questions: 

Q1. A smooth shining surface, which rebounds the light back in the same or in a different direction, is called 

1. A mirror
2. A lens
3. Reflection of light
4. Point of Incidence 

Answer: (i) A mirror 

Q2. The beam of light striking the reflecting surface is called 

1. Reflecting ray
2. Incident ray
3. Refracted ray
4. Normal ray 

Answer: (ii) Incident ray 

Q3. The front bulged part of the eyeball is called

1. Cornea
2. Choroid 
3. Pupil 
4. Retina

Answer: (i) Cornea

Q4. Band of seven colours is called 

1. VIBGYOR 
2. Spectrum 
3. Dispersion
4. Reflection

Answer: (ii) Spectrum 

Q5. Which of the following statements is correct regarding rods and cones in the human eye?

1. Cones are sensitive to dim light 
2. Cones are sensitive to bright light
3. Rods are sensitive to bright light 
4. Rods can sense color 

Answer: (ii) Cones are sensitive to bright light

Class 8 English

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Hope these notes on Class 8 Light helped clear your doubts and explain the chapter to you properly. If you need guidance with any other chapters or with any other subjects check our other blogs on Leverage Edu for help. Hope we will be able to help you get better marks in your exams.