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Q1. Differentiate between luminous objects and non-luminous objects.

Solution

Luminous objects Non-luminous objects Luminous objects are the objects that emit light of their own. Non-luminous objects are the objects that reflect light. Luminous objects are seen on their own. Non-luminous objects are seen due to luminous objects. Example: Sun, candle Example: Moon, mirrors

Q2. What is lateral inversion?

Solution

Lateral inversion is the phenomena when in an image formed by a mirror the left of the object appears on the right and the right appears on the left.

Q3. Which is the most popular resource for visually challenged persons? Who developed it?

Solution

The most popular resource for visually challenged persons is Braille. Louis Braille developed this system and published it in 1821.

Q4. Mention any three possible ways by which we can take care of our eyes.

Solution

(i) If advised, use suitable spectacles. (ii) Do not look at the sun or a powerful light directly. (iii) Wash your eyes frequently with clean water.

Q5. What is iris? Write its function.

Solution

The iris is a dark muscular structure which gives eye its distinct colours. It controls the amount of light entering into the eye.

Q6. After striking the mirror, the ray of light is reflected in another direction. What do we call the ray of light that strikes the mirror and another ray that comes back from the mirror?

Solution

The ray of light that strikes the mirror or any object is called the incident ray. The ray of light that comes back from the mirror or any surface after reflection is called the reflected ray.

Q7. What are the characteristics of Braille system?

Solution

(i) It has 63 dot patterns or characters. (ii) Each character represents a letter, a combination of letters, a common word or a grammatical sign. (iii) Dots are arranged in cells of two vertical rows of three dots each.

Q8. How the visual aids help the visually challenged people?

Solution

Visual aids help people with limited vision to see things. These can magnify words, can provide suitable intensity of light and material at proper distances.

Q9. What protects the interior of the eye from accidents? Where is iris present in the eye?

Solution

The outer coat of the eye is white and tough so that it can protect the interior of the eye from accidents. Iris is present behind the cornea.

Q10. Which phenomena is exhibited in the formation of rainbow? Define it.

Solution

Dispersion of light is the cause of formation of a rainbow. Splitting of light into several colours is called dispersion of light.

Q11. Name some sources of Vitamin A.

Solution

Raw carrots, broccoli and green vegetables (such as spinach), cod liver oil, eggs, milk, curd, cheese etc.

Q12. How do we see various objects?

Solution

When light from an object enters our eyes we see objects. The light may have been emitted by an object, or may have been reflected by it.

Q13. Why moon is considered as an illuminated object?

Solution

Moon is considered as an illuminated object because it receives the light from the sun and reflects it back. Such objects which shine in the light of other objects are called illuminated objects.

Q14. Select the optical aids among the following: Telescopic aids, Bifocal lenses, Tactual aids, Auditory aids, Contact lenses, Tinted lenses.

Solution

Telescopic aids, Bifocal lenses, Contact lenses and Tinted lenses.

Q15. Name the two types of cells which make us see objects and write their function.

Solution

(i) Cones - These are sensitive to bright light and sense colours. (ii) Rods - These are sensitive to dim light.

Q16. What happens if two plane mirrors are used in combinations?

Solution

If two plane mirrors are used in combinations then multiple images are formed.

Q17. What are the uses of periscopes?

Solution

Periscopes are used in submarines, tanks and also by soldiers in bunkers to see things outside.

Q18. What type of image is formed by a plane mirror? Give reason for your answer.

Solution

The image formed by a plane mirror is virtual as the reflected rays do not actually meet but only appear to meet.

Q19. Give reasons for the following: 1. Looking glasses are plane mirrors. 2. A mirror reflects sunlight to give a bright patch of light on the wall, while the lid of the tin gives a less bright patch.

Solution

1. Looking glasses are plane mirrors because the image formed by a plane mirror is always erect and of same size as that of object. 2. A mirror reflects sunlight to give a bright patch of light on the wall because mirror is a polished surface and give regular reflection while the lid of the tin being uneven and rough gives a less bright patch due to diffused reflection.

Q20. How the visually challenged people learn the Braille system?

Solution

The visually challenged people learn the Braille system by beginning with letters, then special characters and letter combinations. Methods depend upon recognition by touching and each character has to be memorized.

Q21. Select the luminous objects among the following: Moon, Chair, Table, Sun, Fire, Electric Lamp, Flame of a candle.

Solution

Sun, Fire, Electric Lamp and Flame of a candle.

Q22. What is the principal behind the working of a Kaleidoscope?

Solution

The principal behind the working of a Kaleidoscope is that a number of images are formed by mirror placed at an angle to another.

Q23. What is angle of incidence and angle of reflection?

Solution

The angle between the normal and the incident ray is called the angle of incidence and the angle formed between the normal and the reflected ray is called the angle of reflection.

Q24. What is cataract? How it can be treated?

Solution

Cataract is a condition in which the eye lens becomes cloudy and the eyesight becomes foggy. It can be treated by surgery. The opaque lens is removed and a new artificial lens is inserted.

Q25. Differentiate between regular reflection and diffused (irregular) reflection.

Solution

Regular Reflection Irregular Reflection

• In regular reflection, all the light that falls on the reflecting surface is reflected in a definite direction.

• In irregular reflection, all the light that falls on the reflecting surface is not reflected in a definite direction.

• It takes place on a smooth highly polished surface.

• It takes place on a rough and uneven surface.

Q26. Why we are able to see the back of our head at dresser's shop?

Solution

We are able to see the back of our head at dresser's shop due to the formation of a number of images by two plane mirrors placed at an angle to one another.

Q27. Mention any three features of the image obtained by a plane mirror.

Solution

Features of the image obtained by a plane mirror are: (i) The image formed is virtual. (ii) The image formed is laterally inverted. (iii) The image formed is of the same size as the object.

Q28. State the laws of reflection.

Solution

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

Q29. How the eye perceives that a still object is moving?

Solution

The impression of an object persists for about 1/16^th of a second. So, if still images of a moving object are flashed on the eye at a rate faster than 16 per second, then the eye perceives that the object is moving.

Q30. What is diffused or irregular reflection?

Solution

When all the parallel rays reflected from a plane mirror are not parallel, the reflection is said to be diffused or irregular reflection.