Q23 of 805 Page 180

A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.

The student is suffering from myopia or short-sightedness. Because the parallel rays coming from longer distance will meet at a point before retina. So doctor will advise him to wear concave lens which will diverge the light rays and focus the rays on retina.


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21

In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.

 22

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

 24

How will you use two identical prisms so that a ray of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

 25

Three 60 W incandescent bulbs are connected in a parallel.

(a) Calculate the total power consumed.


(b) Now suppose that one of the bulbs is fused. What will be the total power consumed now?