Test your knowledge of Class 8 Science Chapter 13, "Light," with this engaging quiz! Covering topics like reflection, refraction, laws of light, and the human eye, this quiz is designed to reinforce key concepts and make learning fun. Perfect for students preparing for exams or revising important topics in a simple and interactive way!
1) How does the sense of sight help us?
Answer: The sense of sight allows us to see mountains, rivers, trees, plants, chairs, people, clouds, rainbows, birds flying in the sky, the moon, the stars, and many other things around us. It also enables us to read words and sentences printed on a page.
2) How is seeing made possible?
Answer: Seeing is possible when light from an object enters our eyes. This light may be emitted by the object itself or reflected off it. Without light, eyes alone cannot see any object.
3) Can we see objects in the dark? Why or why not?
Answer: No, we cannot see objects in the dark because there is no light to enter our eyes from the object. Light is essential for vision.
4) What can act as a mirror, and what does it do?
Answer: A polished or shiny surface can act as a mirror. A mirror changes the direction of light that falls on it.
5) What happens to light when it strikes a mirror?
Answer: When light strikes a mirror, it is reflected in another direction.
6) What is the incident ray?
Answer: The incident ray is the light ray that strikes a surface.
7) What is the reflected ray?
Answer: The reflected ray is the light ray that comes back from the surface after reflection.
8) How can we observe the reflection of light?
Answer: Reflection of light can be observed through the following activity:
Fix a white sheet of paper on a table or drawing board.
Take a comb and close all its openings except one in the middle using a strip of black paper.
Hold the comb perpendicular to the paper.
Throw light from a torch through the opening of the comb.
Adjust the torch and comb to see a ray of light along the paper.
Place a strip of plane mirror in the path of the light ray.
9) What do you observe when a plane mirror reflects a ray of light?
Answer: After striking the plane mirror, the ray of light changes direction and is reflected.
10) What is a ray of light, and how do we simplify its representation?
Answer: A ray of light is an idealization. In reality, light comprises a narrow beam of several rays. For simplicity, we use the term "ray" to refer to a narrow beam of light.
11) What is the normal to a reflecting surface?
Answer: The normal is a line drawn at an angle of 90° to the reflecting surface at the point where the incident ray strikes the mirror.
12) What is the angle of incidence?
Answer: The angle of incidence is the angle between the normal and the incident ray.
13) What is the angle of reflection (∠𝑟)?
Answer: The angle of reflection is between the normal and the reflected ray.
14) How can you measure the angles of incidence and reflection?
Answer: Measure the angle between the normal and the incident ray (∠𝑖) for the angle of incidence, and the angle between the normal and the reflected ray (∠r) for the angle of reflection. These can be recorded by drawing lines and observing the rays after striking a plane mirror.
15) What is the relationship between the angle of incidence and the angle of reflection?
Answer: The angle of incidence (∠i) is always equal to the angle of reflection (∠r), as per the laws of reflection.
16) What would happen if you throw light on the mirror along the normal?
Answer: If light is thrown on the mirror along the normal, it will reflect back along the same path because the angle of incidence and angle of reflection are both 0°.
17) What happens when the whole sheet of paper is spread on the table?
Answer: When the sheet of paper is spread on the table, it represents one plane. The incident ray, the normal at the point of incidence, and the reflected ray all lie in this plane.
18) What happens when you bend the paper?
Answer: When the paper is bent, it creates a plane different from the one in which the incident ray and the normal lie. As a result, the reflected ray is no longer visible.
19) What does this observation indicate about the incident ray, the normal, and the reflected ray?
Answer: This indicates that 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.
20) What alternative source of light can be used for the activities of incidence angle,reflective angle??
Answer: Instead of using a torch, the Sun can be used as the source of light for performing the activities.
21) What tool can be used to perform these activities?
Answer: The activities can also be performed using the Ray Streak Apparatus, which is available in the kit prepared by NCERT.
22) What features of an image formed by a plane mirror(Class 7)?
Answer: The features of an image formed by a plane mirror include:
The image is erect, not upside down.
The image is of the same size as the object.
The image appears at the same distance behind the mirror as the object is in front of it.
The image cannot be obtained on a screen.
23) What is lateral inversion?
Answer: Lateral inversion is the phenomenon where the left of the object appears on the right and the right appears on the left in an image formed by a mirror.
24) What is diffused or irregular reflection?
Answer: Diffused or irregular reflection occurs when parallel rays reflected from a rough or irregular surface are not parallel.
This type of reflection is caused by irregularities in the reflecting surface, such as cardboard.
It is not due to a failure of the laws of reflection.
25) What is regular reflection?
Answer: Regular reflection occurs when rays are reflected from a smooth surface, such as a mirror.
The reflected rays remain parallel, and images are formed as a result.
26) Do we see all objects due to reflected light?
Answer: Nearly everything we see around us is due to reflected light. For example, the moon receives light from the Sun and reflects it, making it visible to us. Objects that shine in the light of other objects are called illuminated objects.
27) What are some examples of illuminated objects?
Answer: Examples of illuminated objects include the moon, planets, and any object that reflects light from another source.
28) What are luminous objects?
Answer: Luminous objects are those that emit their own light. Examples include the Sun, fire, the flame of a candle, and an electric lamp.
29) Can reflected rays be further reflected if incident on another mirror?
Answer: Yes, reflected rays can be further reflected if they strike another mirror. For instance, a hairdresser uses two mirrors to show the back of your head by reflecting light from one mirror to the other.
30) How does a hairdresser use mirrors to show the back of your head?
Answer: The hairdresser holds a second mirror behind you, which reflects the image of the back of your head into the front mirror. This reflection allows you to see the back of your head.
31) What is a periscope, and how does it work?
Answer: A periscope is a device that uses two plane mirrors to reflect light.
The mirrors are placed at an angle to each other, enabling you to see objects that are not directly visible.
Periscopes are used in submarines, tanks, and bunkers to view objects outside.
32) What happens when two plane mirrors are used in combination?
Answer: Using two plane mirrors in combination can produce multiple reflections, forming multiple images of an object.
33) What is observed when a coin is placed between the mirrors set at right angles?
Answer: Multiple images of the coin are seen when it is placed between the mirrors set at right angles.
34) What happens when the angle between the mirrors is changed?
Answer: The mirrors are hinged at different angles (e.g., 45°, 60°, 120°, 180°) using adhesive tape.
A candle or object is placed between them, and the number of images is noted.
35) How many images are formed when the mirrors are parallel to each other?
Answer: When the two mirrors are parallel to each other, infinite images of a candle or object placed between them are formed.
36) How is the concept of mirrors at an angle used in a kaleidoscope?
Answer: The concept of mirrors placed at specific angles is used in a kaleidoscope to produce numerous beautiful patterns.
37) What is kaleidoscope?
Answer: A kaleidoscope is a toy that produces beautiful and ever-changing patterns.
38) How does a kaleidoscope work?
Answer: When you look through the hole, the reflections from the mirrors create a variety of colorful patterns.
39) What is the unique feature of a kaleidoscope?
Answer: You will never see the same pattern twice.
40) What is dispersion of light?
Answer: Dispersion of light is the splitting of white light into its component colors.
41) What is the role of the eye in vision?
Answer: We can only see things when light from them enters our eyes.
42) What is the structure of the human eye?
Answer: The eye is roughly spherical with a tough outer coat for protection. The transparent front part is called the cornea.
43) How does the eye help us see?
Answer: Light enters the eye through the cornea and is focused on the retina. The retina converts light into electrical signals, which are then transmitted to the brain, allowing us to perceive images.
44) What is the cornea?
Answer: The cornea is the transparent front part of the eye.
45) What is the iris?
Answer: The iris is a dark, muscular structure behind the cornea.
46) What is the pupil?
Answer: The pupil is a small opening in the iris.
47) What is the function of the iris?
Answer: The iris controls the size of the pupil, regulating the amount of light entering the eye.
48) How does the iris determine eye color?
Answer: The color of the iris gives a person their eye color (e.g., green eyes).
49) What happens to the pupil when exposed to light?
Answer: The pupil constricts (becomes smaller) when exposed to bright light and dilates (becomes larger) in dim light.
50) Why does the pupil change size?
Answer: The pupil adjusts its size to control the amount of light entering the eye.
51) What is the lens of the eye?
Answer: The lens is located behind the pupil and is thicker in the center.
52) What type of lens is thicker at the center?
Answer: A convex lens.
53) What is the retina?
Answer: The retina is a layer at the back of the eye where light is focused.
54) What are the types of cells in the retina?
Answer: Cones: Sensitive to bright light and color.
Rods: Sensitive to dim light.
55) What is the optic nerve?
Answer: The optic nerve transmits signals from the retina to the brain.
56) What is the blind spot?
Answer: The blind spot is a point on the retina where there are no sensory cells, resulting in no vision.
57) How does the human eye perceive motion?
Answer: The human eye retains an image on the retina for about 1/16th of a second. If still images of a moving object are flashed at a rate faster than 16 per second, the eye perceives it as continuous motion.
58) How are movies created?
Answer: Movies consist of a series of still images shown in rapid succession (usually at 24 frames per second) to create the illusion of motion.
59) What is the function of eyelids?
Answer: Eyelids protect the eye from foreign objects and excessive light.
60) What is the normal range of human vision?
Answer: The normal eye can see both distant and nearby objects clearly.
61) What is the most comfortable reading distance for a normal eye?
Answer: Approximately 25 cm.
62) What are some common vision defects?
Answer: Nearsightedness: Difficulty seeing distant objects clearly.
Farsightedness: Difficulty seeing nearby objects clearly.
63) How can vision defects be corrected?
Answer: By using corrective lenses (glasses or contact lenses).
64) What is cataract?
Answer: Cataract is a condition where the eye lens becomes cloudy, leading to vision loss.
65) How is cataract treated?
Answer: By surgically removing the opaque lens and replacing it with an artificial lens.
66) How can you take care of your eyes?
Answer: Have regular eye checkups.
Use suitable spectacles if advised.
Avoid excessive light or insufficient light.
67) How are animal eyes adapted to their environment?
Answer: Animals have eyes adapted to their specific needs.
Crabs have small eyes that allow them to see in all directions.
Butterflies have large, compound eyes for a wide field of vision.
Owls have eyes adapted for night vision with large pupils and a high concentration of rods.
Day birds have eyes adapted for daytime vision with more cones.
68) How can you protect your eyes from damage?
Answer: Avoid direct exposure to strong light: Never look directly at the Sun or a powerful light source like a laser.
Avoid rubbing your eyes: If dust enters your eyes, wash them with clean water. Consult a doctor if the problem persists.
Maintain proper reading distance: Read at a comfortable distance, neither too close nor too far.
69) How does diet affect eye health?
Answer: A balanced diet is crucial for eye health.
Vitamin A deficiency can lead to night blindness.
Include foods rich in vitamin A in your diet, such as carrots, spinach, broccoli, eggs, milk, and fruits like papaya and mango.
70) How can visually impaired people live independently?
Answer: Visually impaired individuals develop other senses, such as touch and hearing, more acutely.
They can also benefit from assistive technologies and resources to enhance their capabilities.
71) What are non-optical aids for the visually impaired?
Answer: Non-optical aids are assistive devices that help visually impaired individuals using senses other than sight. They include:
Visual aids: Magnifiers, suitable lighting, and materials at appropriate distances.
Tactual aids: Braille writer slate and stylus, for reading and writing Braille.
Auditory aids: Cassettes, tape recorders, talking books, and other audio devices.
Electronic aids: Talking calculators, computers, closed-circuit television (CCTV), and voice boxes.
72) What are optical aids for the visually impaired?
Answer: Optical aids are devices that assist vision by correcting or improving visual function. They include:
Bifocal lenses: Correct both nearsightedness and farsightedness.
Contact lenses: Correct refractive errors like nearsightedness, farsightedness, and astigmatism.
Tinted lenses: Reduce glare from sunlight or artificial light.
Magnifiers: Enlarge printed material.
Telescopic aids: Help view distant objects like chalkboards and class demonstrations.
73) What is the Braille system?
Answer: The Braille system is a tactile reading and writing system for the visually impaired, developed by Louis Braille.
74) How does the Braille system work?
Answer: It uses 63 dot patterns arranged in cells of two vertical rows of three dots each. Each pattern represents a letter, a combination of letters, a word, or a grammatical sign.
75) When was the current Braille system adopted?
Answer: The present Braille system was adopted in 1932.
76) What languages can be read using Braille?
Answer: Braille codes exist for common languages, mathematics, and scientific notation. Many Indian languages can also be read using Braille.
77) How do visually impaired people learn the Braille system?
Answer: Visually impaired people learn the Braille system by first learning individual letters, then progressing to special characters and letter combinations.
78) What is the primary method of recognition in Braille?
Answer: The primary method of recognition in Braille is through touch.
79) How are Braille texts produced?
Answer: Braille texts can be produced both by hand and by machine.
80) What advancements have been made in Braille technology?
Answer: Typewriter-like devices and printing machines have been developed to produce Braille texts.
81) Can you name some visually impaired Indians who have achieved great success?
Answer: Yes, some notable examples include:
Diwakar: A child prodigy who has given amazing performances as a singer.
Ravindra Jain: Born completely visually impaired, he obtained his Sangeet Prabhakar degree from Allahabad and excelled as a lyricist, singer, and music composer.
Lal Advani: Established an Association for special education and rehabilitation of disabled in India and represented India on Braille problems in UNESCO.
82) Who is Helen A. Keller?
Answer: Helen A. Keller was an American author and lecturer, renowned as one of the most inspiring visually challenged individuals.
83) What happened to Helen A. Keller when she was young?
Answer: Helen A. Keller lost her sight when she was only 18 months old.
84) Despite her disability, what significant achievement did Helen A. Keller accomplish?
Answer: Despite losing her sight, Helen A. Keller was able to complete her graduation from a university.
85) What notable work did Helen A. Keller author?
Answer: Helen A. Keller wrote several books, including "The Story of My Life" (1903).
