NCERT Class 8 Science Chapter 16 - Light Extra Questions

Chapter 16 - Light Extra Questions

One Word Answer Questions
Question 1: What is the nature of the image formed by the plane mirror?
Answer:
The nature of the image formed by the plane mirror are
• Image distance and object distance are equal
• Size of the object and image are equal
• The image formed is erect and virtual

Question 2: Where is the image formed in a plane mirror?
Answer:
The image formed in a plane mirror is in front of plane mirror.

Question 3: What do we call the image that cannot be obtained on a screen?
Answer:
The image that cannot be obtained on a screen are called virtual images.

Question 4: Name the phenomenon shown in the figure.

Fig 1

Answer: The phenomenon shown in the figure is Lateral Inversion.

Question 5: How many colours are there in a spectrum of white light?
Answer:
There are 7 colours in a spectrum of white light (VIBGYOR).

Very Short Answer Questions
Question 6: Define light.
Answer:
Light is a form of energy that enables us to see.

Question 7: What is reflection?
Answer:
Reflection happens when light rays fall on an object their direction changes and they turn back.

Question 8: What is a mirror?
Answer:
A smooth and high polished reflecting surface is called mirror. There are 3 types of mirror - Plane mirror, Concave mirror and Convex mirror.

Question 9: State the two laws of reflection.
Answer:
The two laws of reflection are
• The angle of incidence is equal to angle of reflection.
• The incident ray, normal and reflected ray, all lie in a same plane.

Question 10: Differentiate between rod and cone cells.
Answer:

• Rods are sensitive to dim light.
• The cones are sensitive to bright light and colour.

Short Answer Questions
Question 11: Write a note on ‘The Human Eye’.
Answer:
The eye has a roughly spherical shape. The outer coat of eye is white. It is tough so that it can protect the interior eye from accidents. It consists of
• Cornea
• Iris
• Lens
• Ciliary muscles
• Retina
• Optic nerve

Question 12: Write the ways to protect your eyes.
Answer:
Some ways to protect our eyes are
• If there is any problem of the eyes have a checkup and use suitable spectacles if advised.
• Too little or too much light is bad for eyes.
• Don't look at the sun or very bright light directly. • If dust particles enter the eye don't rub the eyes. Wash your eyes with clean water.
• Always read at a normal distance. Don't read the keeping the book to close to the eyes or keeping it too far.
• Deficiency of Vitamin A causes night-blindness. So take food rich in Vitamin A.

Question 13: Explain some common eye defects in human.
Answer:
The normal human eye can see nearby as well as distant objects clearly. The minimum distance at which objects can be seen clearly is 25 cm.  Some persons can see nearby objects clearly but cannot see distant objects clearly. Some persons can see distant objects clearly but cannot see nearby objects clearly. These defects can be corrected by using suitable corrective lenses.  Sometimes in old age people cannot see clearly because the eye lens becomes cloudy. This defect is called cataract. It can be corrected by removing the eye lens and replacing it with an artificial lens.

Question 14: What kind of lens is there in our eyes? Where does it form the image of an object?
Answer:
The lens that is present in our eyes is convex lens. It focuses the light on the back of the eyes, the retina. As a result, it creates an image of an object in the retina. There are sensory cells that detect the light. There are 2 types in retina namely the rods and the cones. Rods are sensitive to dim light. The cones are sensitive to bright light and colour.

Question 15: What is power of accommodation?
Answer:
Power of accommodation is the ability of the eye lens to focus near and far objects clearly on the retina by adjusting its focal length.

Long Answer Questions
Question 16: While playing, something entered into Somya’s eye. She immediately washed her eye with cold water. But as the irritation persisted, she immediately reported to her class teacher. Her class teacher took her to an eye doctor. What should be done if some foreign particles enter your eyes? Why is it not advised to rub your eyes when there is an eye irritation due to foreign particles? Do you think Somya was right in her action? What value of Somya is seen here?
Answer:
Foreign objects may cause damage our cornea on rubbing. It may also cause the bleeding of cornea. Yes, Somya was right in her actions. She didn’t let her eyes to be damaged. Somya is an intelligent girl and very careful and conscious for her health. She is also having scientific knowledge.

Question 17: Meet an eye specialist. Get your eye sight checked and discuss how to take care of your eyes.
Answer:

• If there is any problem of the eyes have a checkup and use suitable spectacles if advised.
• Too little or too much light is bad for eyes.
• Don't look at the sun or very bright light directly.
• If dust particles enter the eye don't rub the eyes. Wash your eyes with clean water.
• Always read at a normal distance. Don't read the keeping the book to close to the eyes or keeping it too far.
• Deficiency of Vitamin A causes night-blindness. So take food rich in Vitamin A.


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