Q25 of 56 Page 1

Different paths of ray are shown in the following figures. Which of the following is correct:


Figures 1 and figure 2 are wrong because in figure 1, the image is not formed at focus and in figure 2, when the object is at infinity, the image is formed at focus. In figure III, the image is correct, the angle of incidence is equal to the angle of reflection.

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23

(a) What is meant by ‘power of a lens’?

(b) State and define the S.I. unit of power of a lens.


(c) A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with each other. Calculate the lens power of this combination.

 24

(a) Draw a ray diagram to show the formation of image of an object placed between infinity and optical center of a concave lens.

(b) A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate


(i) the distance of the object from the lens


(ii) the magnification for the image formed


(iii) the nature of the image formed -

 26

In these diagram, the angle of refraction r is correctly marked in which diagram?

 27

To find the focal length of a concave mirror, Sita should choose which one of the following set-ups?