NCERT Solutions Class 8 Science Chapter 16

NCERT Solutions for Class 8 Science Chapter 16

NCERT Class 8 Science Chapter 16 is Light. This chapter focuses on the electromagnetic radiations that may be recognized by human vision and are referred to as visible light. The electromagnetic spectrum is quite vast, ranging from low-energy radio waves with wavelengths in meters to a high-energy gamma-ray with a wavelength of fewer than 1×10-11 meters. Magnetic fields are fluctuated by electromagnetic radiations, which transmit energy at the speed of light. A stream of photons and massless energy packets are other terms for light. The photon is the smallest unit of energy that can be transferred.

Students may find it tricky to understand the concepts when it comes to a chapter such as light. However, it becomes easier to comprehend the chapter if the students refer to Class 8 Science Chapter 16 Solutions by Extramarks. This is because class 8, Chapter 16  NCERT Solutions, is developed exclusively by Extramarks experts, keeping in mind all the needs of the students.

Extramarks Class 8 Science Chapter 16 benefits the students in grasping all minor and significant concepts of the chapter. Apart from NCERT Solutions for Class 8 Science Chapter 16- Light, NCERT Solutions of other chapters and subjects, Additional Questions, Sample Papers, Revision Notes, CBSE past years’ question papers, and a lot more can be found on the Extramarks website.

Key Topics Covered in NCERT Solutions for Class 8 Science Chapter 16

Given is the list below of the key topics that are covered in NCERT Solutions for Class 8 Chapter 16 Science:

 Introduction to Light Laws of Reflection Types of Reflection Difference between Real and Virtual Image Dispersion Human Eye The Braille System

Let us look at Extramarks’ in-depth information on each subtopic in NCERT Solutions for Class 8 Science Chapter 16- Light.

Introduction to Light

Extramarks NCERT Solutions for Class 8 Science Chapter 16 briefly introduces light in this section.

The world as we know is mainly understood through our senses, with sight being one of the most crucial senses. Objects can only be seen when light falls onto the object and is reflected back to our eyes to form an image in our brain.. The following are some key terms linked to light:

The energy that allows us to see is known as light. A source of light, such as the Sun, emits light. The term generally refers to visible light i.e visible to the naked eye and responsible for our ability to see.

How do we see objects?

When light falls on an object from the source of light (mainly, sun) it gets reflected in all directions. The reflected light then reaches our eyes and our brain perceives the image of that object.

Laws of Reflection

Light is reflected off of many surfaces. Any highly polished or gleaming surface can work as a mirror and reflect light. The phenomenon of lighting reflecting or bouncing off light from any surface is known as Reflection.

Extramarks NCERT Solutions for Class 8 Science Chapter 16 defines the law of reflection as:

The principle when a ray of light falls on a smooth surface and the angle of reflection is equivalent to the angle of incidence, also the incident ray, reflected ray, and normal to the surface, all lie in the same plane.

Laws of Reflection

• The incident ray is that ray of light that strikes a reflecting surface, while the reflected ray is the ray reflected.
• The normal is an imaginary line that is perpendicular to the reflecting surface.
• The incidence angle (I) is the angle formed by the incident ray and the normal. The angle between the reflected beam and the normal is called the angle of reflection (r).
• The angle of incidence (I) is always equal to the angle of reflection (r),  (i=r) according to the laws of reflection. This is because the normal, the angle of incidence, and the angle of reflection are all on the same plane.

Types of Reflection

Extramarks NCERT Solutions for Class 8 Science Chapter 16 explains the two types of Reflection here:

Regular Reflection

Flat mirrors produce this form of reflection with a smooth surface, thus resulting in a crisp picture which can be easily seen. However, plane mirror pictures are always virtual, which means they can’t be gathered on a screen.

We can observe the pictures of reflection either digitally or physically in the case of curved mirrors with a smooth surface. Curved mirrors can create actual or virtual pictures, which can be gathered and viewed (cannot be collected on a screen but only seen).

Diffused Reflection

Unlike mirrors, most natural surfaces are rough on the scale of light wavelengths, and as a result, parallel incident light rays are reflected unevenly or diffusely in many distinct directions. As a result, diffuse reflection aids in object recognition and is responsible for the ability to perceive most lighted surfaces from any angle.

Image formation in a plain mirror

• A plane mirror’s image is always virtual and upright, and the object and image are always equidistant from the mirror.
• A lateral inversion occurs when an image is created in a planar mirror.

Difference between Real and Virtual Image

The actual convergence of light beams creates a real image. A virtual image is generated when the outgoing rays from a spot on an object constantly diverge in optics. The picture looks to be situated around the clear divergence point. A virtual image cannot be projected onto a screen because the rays never indeed converge.

Multiple Reflections

• Due to numerous reflections, two mirrors inclined to each other produce several images .
• Infinite pictures are generated when an item is held between two parallel plane mirrors.

Extramarks NCERT Solutions for Class 8 Science Chapter 16 discusses the concept of Real and Virtual images and multiple reflections in the above section. To find answers to various such questions, refer to Extramarks today.

Dispersion

Another important aspect that we come across in Extramarks NCERT Solutions for Class 8 Science Chapter 16 is the concept of Dispersion.

When white light passes through a glass prism, it separates into its spectrum of colors (in sequence violet, indigo, blue, green, yellow, orange, and red), a process known as  Dispersion.

Dispersion in a prism is the easiest method to describe the process: A spectrum of seven colors is generated when white light passes through a prism, demonstrating that white light is a blend of seven distinct hues. Prism serves as a separating medium for the seven hues. Refraction occurs when light strikes the glass prism. Because the wavelengths of specific light components fluctuate while the frequency remains constant, the variation in velocity through the glass medium causes each member to diverge at a different angle. The color red, which has the longest wavelength, deviates the least and forms the top portion of the spectrum, whereas violet, which has the shortest wavelength, deviates the most and includes the lower half.

Human Eye

Let us take a glance at the fundamental concept of Human Eyes by Extramarks NCERT Solutions for Class 8 Science Chapter 16.

The eye is one of the most powerful and sophisticated sense organs we humans possess. It helps visualize things and light, color, and depth perception. Furthermore, these sense organs can be compared to cameras in the way that they assist humans in seeing objects when light from the outside enters the objects. So, learning about the anatomy and operation of the human eye is fascinating. It also assists us in comprehending how a camera operates.

How do different organs in the Human Eyes function?

• Light enters the eye through a thin membrane called the cornea, which produces a transparent protrusion in the front of the eye.
• Iris is a black muscular diaphragm that regulates pupil size.
• The pupil is the iris’s tiny aperture in the middle.
• The lens behind the pupil assists in adjusting the focal length necessary to concentrate clearly on things at varying distances.
• The retina is the screen on which pictures are created. It is a fragile membrane that contains a vast number of photosensitive rods and cones.
• Bright light makes cones sensitive, whereas low light makes rods sensitive.

Visual Defects

• Visual deficiencies are the inability to see close items or view far away objects.
• The eye lens becomes clouded as people age, resulting in vision loss.

The Braille System

The idea of the Braille system is a significant part of Extramarks NCERT Solutions for Class 8 Science Chapter 16.

It was created specifically for the blind by Louis Braille. It’s raised-dot lettering that may be recognized by touching it with the fingertips. All Braille letters are made up of six dot locations organized in a rectangle with two columns of three dots each. A dot can be raised in any position.

Braille codes are made up of alphabet dot patterns, symbols, and other punctuation. It is carried out in a consistent manner and is based on Louis Braille’s original assignments. Various Braille codes are also used to notate mathematics, computer applications, music, and chess systems. The base of this code is still the 64 potential Braille letters and the added notational components.

NCERT Solutions for Class 8 Science Chapter 16 Exercise and Solutions

Students can find NCERT Solutions for all chapters and other study tools, including past years’  question papers, revision notes, extra problems, and more, on the Extramarks website. Click on the below links to view NCERT Solutions for Class 8 Science Chapter 16:

Class 8 Science Chapter 16: Very Short Answer Type Questions

Class 8 Science Chapter 16: Short Answer Type Questions

Class 8 Science Chapter 16: Long Answer Type Questions

Students may access NCERT Solutions for Class 8 Science Chapter 16 and other chapters by clicking here. In addition, students can also explore NCERT Solutions for other classes below.

• NCERT Solutions Class 1
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• NCERT Solutions Class 3
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• NCERT Solutions Class 5
• NCERT Solutions Class 6
• NCERT Solutions Class 7
• NCERT Solutions Class 8
• NCERT Solutions Class 9
• NCERT Solutions Class 10
• NCERT Solutions Class 11
• NCERT Solutions Class 12

By getting access to NCERT Solutions for Class 8 Science Chapter 16- Light, students can easily understand all the chapter’s concepts which are included in the detailed answers of the NCERT questions of this chapter.

Key Features of NCERT Solutions for Class 8 Science Chapter 16

Extramarks customizes its NCERT Solutions in such a way that it meets all the requirements of the students. Moreover, these solutions are prepared to the point in an elaborate manner. As a result, the Solutions are highly beneficial to students and help them understand things more easily and rapidly. Let us give you some reasons why you should choose us:

• Based on the NCERT standards, Extramarks has compiled the most relevant material in this chapter.
• These solutions also help students with time management during their examinations.
• These solutions have been prepared in a simple yet detailed manner for the students to understand complex and intricate topics easily and quickly.

Q.1 Suppose you are in a dark room. Can you see objects in the room? Can you see object outside the room? Explain.

Ans-

If we are in a dark room, we cannot see the objects kept inside the room. On the other hand, objects outside the room can be seen. An object becomes visible when light reaches our eye after being reflected from the object. If there is no light in the room, then the objects inside the room will not reflect any light. Hence, we cannot see in a dark room. If there is light present outside the room, then objects placed outside the room can be seen.

Q.2 Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?

Ans-

When all parallel rays reflected from a smooth, polished and regular surface are parallel, then the reflection is known as a regular reflection . Clear images are formed by regular reflection. Water and mirror are some of the examples of smooth surface. If all parallel rays reflected from an irregular surface are not parallel, then the reflection is known as an irregular or diffused reflection. It is caused by irregularities in the reflecting surface and we see hazy image or no image at all. A cardboard and a wall are some of the examples of irregular surface.In diffused reflection, each ray obeys the laws of reflection. Therefore, laws of reflections are not violated.

Q.3 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.

(a) Polished wooden table
(b) Chalk powder
(c) Cardboard surface
(d) Marble floor with water spread over it
(e) Mirror
(f) Piece of paper

Ans-

(a) Polished wooden table (Regular reflection)
Explanation: A polished wooden table acts as a smooth surface. Hence, reflections from the polished table will be regular.

(b) Chalk powder (Diffused reflection)
Explanation: Chalk powder is not an example of smooth surface. Therefore, diffused reflection will take place from chalk powder.

(c) Cardboard surface (Diffused reflection)
Explanation: Cardboard surface is also an example of an irregular surface. Hence, diffused reflection will take place from a cardboard surface.

(d) Marble floor with water spread over it (Regular reflection)
Explanation: Water makes marble surface smoother. Hence, regular reflection will take place from this surface.

(e) Mirror (Regular reflection)
Explanation: Mirror has a smooth surface. Therefore, it will give a regular reflection.

(f) Piece of paper (Diffused reflection)
Explanation: A piece of paper has many irregularities on its surface. Hence, it will give a diffused reflection.

Q.4 State the laws of reflection.

Ans-

There are two laws of reflection:

1. The angle of reflection is always equal to the angle of incidence.
2. The incident ray, the reflected ray and the normal to the reflective surface at the point of incidence all lie in the same plane.

Q.5 Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

Ans-

Choose a place in the room where light is very dim. Place a plane mirror on the table. Take a paper sheet and make a small hole in its centre. Hold the sheet normal to the table. Take another sheet and place it on the table in contact with the vertical mirror. Now, draw a normal line on the second sheet from the mirror. Light a torch on the mirror through the small hole in such a way that the ray of light falls on the normal at the bottom of the mirror. When the ray from this hole is incident on the mirror, it gets reflected in a certain direction. Now, it can be observed that the incident ray, reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.

Q.6 Fill in the blanks in the following.

(a) A person 1 m in front of a plane mirror seems to be ___ m away from his image.
(b) If you touch your ___ ear with your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with ____.
(c) The size of the pupil becomes ___ when you see in dim light.
(d) Night birds have ___ cones than rods in their eyes.

Ans-

(a) A person 1 m far from a plane mirror seems to be 2 m away from his image.
Explanation: Object distance and image distance are the same from a plane mirror. Therefore, the image distance = 1 + 1 = 2 m away from the person.

(b) If you touch your left ear with your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with your left hand.
Explanation: It is because lateral inversion.

(c) The size of the pupil becomes large when you see in dim light.
Explanation: It is because the amount of light entering into the eye becomes very less. Hence, to increase the amount of light, the pupil expands.

(d) Night birds have less cones than rods in their eyes.
Explanation: Night birds cannot see in the day but can see in the night. They have a few cones and a large number of rod cells on their retina.

Q.7 Angle of incidence is equal to the angle of reflection.

(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never

Ans-

The correct option is (a).

Explanation: According to first law of reflection, the angle of incidence is always equal to the angle of reflection.

Q.8 Image formed by a plane mirror is

(a) virtual, behind the mirror and enlarged.
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.

Ans-

The correct option is (b).

Explanation: The image formed by a plane mirror is of the same size as the object and is formed behind the mirror. The image cannot be obtained on a screen. Therefore, it is a virtual image.

Q.9 Describe the construction of a kaleidoscope.

Ans-

Take three rectangular mirror strips each about 15 cm long and 4 cm wide. Group them with their long edges together to form a prism. Place and fix them inside a circular cardboard tube or a tube made up of a thick chart paper. Note that the tube must be slightly longer than the mirror strips. Cover one end of the cardboard tube by a cardboard disc. This disc must have a hole at its centre through which we can see. Paste a piece of transparent plastic sheet under the disc in order to make it durable. Fix a circular plane glass plate at the other end of the tube. Place some small pieces of coloured glass on this glass plate. Cover this end of the tube with the ground glass plate and keep enough space for the coloured glass pieces to move. The kaleidoscope is ready. If we look through the hole of the kaleidoscope, beautiful image can be seen.

Q.10 Draw a labelled sketch of the human eye.

Ans-

The different parts of the human eye have shown here.

Q.11 Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise?

Ans-

For human eyes, laser light is dangerous as it’s intensity is very high. It can harm to the retina. Therefore, it is advisable not to look at a laser beam directly.

Q.12 Explain how you can take care of your eyes.

Ans-

The given points should be taken into account to protect our eyes:

1. Do not view the sun or the powerful lights directly.
2. When advised by doctor, use suitable and proper spectacles.
3. Too little and too much light is harmful for eyes. Little light leads to eyestrain and headaches while too much light like light from the sun, a powerful lamp or a laser torch can damage the retina.
4. We should never rub our eyes. When the particles of dust go into our eyes, then we should wash our eyes with clean water or else we should visit to a doctor.
5. Maintain a distance of at least 25 cm between the book and your eyes while reading.

Q.13 What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

Ans-

$\begin{array}{l}\text{According to the law of reflection},\text{the angle of incidence is equal to the angle of reflection}.\\ \text{Let, Angle of incident = i}\\ \text{Angle of reflection = r}\\ \text{As per law of reflection,}\\ \text{i = r}\\ \because \text{i + r = 90}°\\ \text{or, i + i = 90}°\\ \text{or, i =}\frac{90°}{2}=45°\\ \text{Therefore, both, angle of incident and angle of reflection will be 45}°\text{.}\end{array}$

Q.14 How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

Ans-

When two mirrors are placed parallel to each other, then infinite numbers of images are formed due to multiple reflections between the mirrors.

Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.

Here, the first law of reflection can be used to obtain the path of reflected light. The given ray of light will reflect from the second mirror at an angle 60°.

Boojho stands at A just on the side of a plane mirror as shown in Fig.16.20. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?

A plane mirror always forms a virtual image behind the mirror and the image distance is equal to the object distance. Boojho cannot see his image because the length of the mirror is too short on his side. Though, he can see the objects placed at points P and Q, but cannot see the object placed at point R.

(a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.21).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?

(a) Image (A’) of the object (A) is formed behind the mirror. The distance of the image from the mirror is equal to the distance of A from the mirror.
(b) Yes. Paheli can see this image at B.
(c) Yes. Boojho can see this image at C.
(d) Image (A’) of the object at A remain at the same position when Paheli moves from B to C.