Q42 of 112 Page 311

What makes things visible to us? Why cannot we see a book which is placed (a) behind a wooden screen, and (b) in a dark room?

Light makes things visible to us. We see an object when light passing through it is reflected.

We cannot see a book which is placed


a- Behind a wooden screen because the wooden screen is opaque so it does not allow light to pass through it.


b- In a dark room because there is no light to be reflected by the book. Thus, due to no reflection, the book is not visible.


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40

Fill in the following blanks with suitable words:

(a) The angle of ................ equals the angle of reflection.


(b) A person 1 m in front of a plane mirror seems to be......... m away from his image.


(c) If you touch your.........ear with right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with..........


(d) The size of pupil becomes...........when you see in dim light.


(e) Night birds have.........cones than rods in their eyes.


(f) The image of an object persists on the retina of an eye for about.........second even after the object has disappeared.


(g) If the still pictures of a moving object are flashed on our eyes at a rate faster than..............pictures per second, the eye perceives the object as moving.


(h) In a movie, the still pictures in proper sequence are projected on the screen usually at the rate of ...........pictures per second.

 41

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

 43

We can see the sun because it is glowing. How are we able to see the moon?

 44

Name the two types of reflection of light. Which type of reflection makes us see an object from all directions?