Light

Question 1

What makes things visible?

Answer 1

It is only when light from an object enters are eyes that we see the object the light may be have been emitted by the object ( luminous objects ) or may have been reflected by it ( illuminated objects ).

Question 2

What is incident ray and reflected ray?

Answer 2

The light ray with strikes any surface is called the incident ray whereas, the ray that comes back from the surface after reflection is known as the reflected ray.

Question 3

What is normal Ray? how is it helpful?

Answer 3

A line making an angle of 90 degree to the line representing the mirror at the point where the incident ray strikes the mirror this line is known as the normal tree to the reflecting surface at that point. It is an imaginary ray which is made to calculate the angles of incidence and reflection.

Question 4

Where do the angle of reflection and angle of incidence lay at ?

Answer 4

The angle of incidence (📐i) is found between the normal and incident ray and the angle between the normal and the reflected ray is known as the angle of reflection (📐r).

Question 5

Name the laws of reflection?

Answer 5

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

Question 6

What are the features of the image formed on a plane mirror?

Answer 6

The image is erect and virtual.
The image is of the same size as the original object.
The image appears double distance behind the mirror as of the object.
The image is laterally inverted.

Question 7

What is lateral inversion?

Answer 7

In an image formed by a mirror the left side of the object appears on the right and the right appears on a left this phenomena is known as lateral inversion It is seen in the plane mirror.

Question 8

What is the difference between diffuse and regular reflection?

Answer 8

• When all the parallel rays reflected from a rough or irregular surface are not parallel the reflection
is known as diffuse or irregular reflection.It is formed on irregular surfaces such as like that of
a cardboard.
• Regular reflection from a Smooth surface like that of a mirror is called regular reflection.Images are formed by regular reflection.

Question 9

How do we see light around us?

Answer 9

Nearly everything you see around is seeing you reflective light.

Question 10

Explain the statement and give examples ‘ reflected light can be reflected again ‘.

Answer 10

Reflected light can be reflected again this phenomena helps us a lot in our daily lives. It’s literal meaning is that two plane mirrors are used in it and a reflected ray gets into the other mirror and forms a optical illusion.
Examples are:
- Hair dresser uses of mirror behind you to show how the hair has been cut. And in barber shop money mirrors are present which bounce back the already reflected rays.
- It is used in periscopes used for submarine stanks and also by soldiers in bankers to see things outside.
- It is used in kaleidoscope to create a number of images or patterns.

Question 11

What is dispersion of light?

Answer 11

The splitting off light into its colors or constituents is known as dispersion of light. It usually disperses into VIBGYOR which is the color of rainbows. It is done by object such as CDs, bulbs or prisms. A prism is put upright when we need to disperse the light and the prism is put upside down when we need to make the dispersed light colours again into normal light. Moreover, the air around us is a mixture of different colors which seems to be normal when mixed together.

Question 12

Describe the structure of our eye? How does it work ?

Answer 12

Eye is one of our most important sense organs. It has a roughly 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 is the transparent front part called Cornea, behind the cornea we find a dark mascular structure called Iris. The iris controls the size of a small opening called pupil. It is the part of the eye which gives it a distinctive color, the iris controls the amount of light entering into the eye. There is a lens which is located behind the pupil, this lens focuses the light on the back of the eye on a layer called Retina. The Retina contains several nerve cells called cones and rods. The sensations felt by these cells are then transmitted to the brain through the optic nerve.

Question 13

What are cons and rods?

Answer 13

Cones and rods are located at the nerve cells which are sensitive to bright light and sensitive to dim light respectively.

Question 14

What is a blind spot?

Answer 14

At the junction of the optic nerve and the retina, there are no sensory cells, So, the vision is not possible at that spot. This spot is known as the blind spot.

Question 15

What is persistence of vision?

Answer 15

The impression of an image does not vanish immediately from the retina it persists there for about 1/16 of a second. so if still images of a moving image are flashed on the eye at the rate faster than 16 images per second then the eye possess this image as moving this phenomena is used in movies by moving separate pictures and proper sequence they used 24 pictures per second.

Question 16

What is the most comfortable distance at which one can read with normal eye?

Answer 16

25 cm

Question 17

What is cataract? How can we treat it?

Answer 17

Sometimes, particularly in old age eyesight becomes foggy, eyesight becomes cloudy When this happens people are said to have cataract. There is a loss of vision sometimes extremely severe. It is possible to treat this defect. The opaque lens is removed and a new artificial lens is inserted.

Question 18

How can we take care of our eyes?

Answer 18

It is necessary that we take proper care of our eyes we can do so by:
- Consulting an eye specialist whenever needed and have regular check ups
- If advised us using suitable spectacles
- Too little or too much light is bad for our eyes as dim light causes eye strain and headache and too much light like that of the sun a powerful source like lamp or a laser torch can damage the retina.
- Do not look at the sun or a powerful light directly
- Never rub your eyes as particles of dust from our hands will go into our eyes and our eyes will get damaged.
- Always read at a normal distance for vision, do not read by bringing the book close to your eyes or keeping it too far.
- We can maintain good eyes by having balanced diet with vitamin A foods like raw carrots, broccoli, green vegetables, eggs, milk, curd, cheese, butter, cod liver oil and fruits like papaya and mango. as deficiency in vitamin A can cause night blindness.

Question 19

How can we help visually impaired persons to read and write?

Answer 19

These people have very limited vision to see things due to a disease or an injury of from birth. The develop there other senses more sharply helping them to live in this society. Furthermore there are non-optical and optical aids for them. Non optical-aids include visual aids, tactual aids (using the sense of touch for example braille script), auditory aids (using the sense of hearing for example cassettes, tape recorders, talking books and other devices) and electronic aids (talking calculators, books, computers, and close circuit television). Whereas optical aids include bifocal lenses, contact lenses, tinted lenses, magnifiers and telescopic aids (they are available to view chalkboard and class demonstrations)

Question 20

Describe the Braille script and tell about some other visually impaired people’s achievements.

Answer 20

• Louis Braille, himself a visually impaired person developed a system for visually challenged people and published it in 1821. The system that we have today was adopted in 1932. The Braille code is present for common languages in India, mathematics and scientific notations. Braille script has 63 dot patterns, each character representing a letter, accommodation of letter, a common word or a grammatical sign. The dots are arranged in two vertical rows of three dots each, to make them easier to touch, the dots are raised slightly which is also an example of tactual aid. Braille Text can be produced by hand or by machines, typewriter like devices and printing machines have now been developed.
• Diwakar, a child prodigy has given amazing performances as a singer.
• Ravindra Jain, born completely visually impaired obtained his Sangeet Prabhakar degree from Allahabad. He has excellence in lyrics writing, singing and music composing.
• Lal Advani himself visual impaired, established an association for special education and rehabilitation of disabled in India, besides this, he represented India on Braille problems in UNESCO.
• Helen Keller, an American author and lecturer is perhaps the most well known and inspiring visually challenged person, she lost her sight when she was only 18 months old but because of her resolve and courage she could complete her graduation from a University , she wrote number of books including the story of my life (1903).