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Chapter 16 Light Solutions

Question - 11 : - Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise?

Answer - 11 : -

Her teacher advised her not to do so because of the intensity of the laser light is very high, it is harmful to the human eyes. It can cause damage to the retina and leads to blindness. Hence, it is advisable not to look at a laser beam directly.

Question - 12 : - Explain how you can take care of your eyes.

Answer - 12 : -

The following points help a person to take care of his eyes:

a) Reading should not be done in bright light as well as in dim light.

b) He should visit an eye specialist on a regular interval of time.

c) If any small insects or dust particles enters his eyes, do not rub them but clean them immediately with cold water.

d) He should avoid direct exposure of sunlight to the eye.

e) While reading, there should be a distance of at least 25 cm between the eyes and the book.

Question - 13 : - What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

Answer - 13 : -

If the reflected ray is at the angle of 90o to the incident ray, then the angle of incidence is 45o. According to the law of reflection, the angle of incidence and the angle of reflection are equal. Therefore, the angle of incidence and the angle of reflection both are 90/2=45o.

Question - 14 : - How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

Answer - 14 : -

If a candle is placed between two parallel plane mirror separated by 40 cm, then the multiple and infinite images will be formed due to the multiple reflections between the mirrors. The infinite numbers of images are formed when two mirrors are placed parallel to each other.

Question - 15 : - Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.

Answer - 15 : -

The first law of reflection is used to obtain the path of reflected light.

It can be observed that the given ray of light will reflect from the second mirror at an angle of 60°.

Question - 16 : -
a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.21).

(b) Can Paheli at B see this image?

(c) Can Boojho at C see this image?

(d) When Paheli moves from B to C, where does the image of A move?

Answer - 16 : -

a) Image of an object placed at A is formed behind the mirror. The distance of the image from the mirror is equal to the distance of A from the mirror

b)Yes Paheli at B can see this image.

c) Yes Boojho at C can see this image.

d) Image of the object at A will not move. It will remain at the same position when Paheli moves from B to C.

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