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##### (iii) If an objcct is situated between the optical centre and the principal focus of a convex lens then its image is formed on the same side as that of the object. This image will be(a) inverted real and bigger in size (b) inverted real and of the same size as that of object (c) inverted real and smaller in size (d) erect virtual and large in size.

Example 4.2 Light passes from air into diamond with an angle of incidence of 45^{\circ} . Calculate the angle of refraction if the index of refraction of diamond is 2.42 .

An astronomical telescope having magnifying power of 5 consist of two thin lenses 24 \mathrm{~cm} apart. Find the focal lengths of the lenses.

(v) A convex lens is(a) thinner at the centre (b) thicker at the centre (c) a diverging lens (d) plane throughout

4.2 The speed of light in water is 2.25 \times 10^{5} \mathrm{~km} / \mathrm{s} . What is the index of refraction of water?

Example 4.6 Calculate the distance of the object from a convex lens having a focal length of 15 \mathrm{~cm} if the magnification is 3 and the image is real.

A converging lens of focal length 5.0 \mathrm{~cm} is used as a magnifying glass. If the near point of the observer is 25 \mathrm{~cm} and the lens is held close to the eye. Calculate (i) the distance of the object from the lens.