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$Example 10.7 An astronomical telescope has an objective lens whose power Is 2 dioptres. This lens is placed 60 \mathrm{~cm} from the eye plece. When the telescope is adjusted for minimum eye strain. Calculate the angular magnification of the telescope.$

$12.8. An object 4 \mathrm{~cm} high is placed at a distance of 12 \mathrm{~cm} from a convex lens of focallength 8 \mathrm{~cm} . Calculate the position and size of the image. Also state the nature of the image.Ans. (24 \mathrm{cm} 8 \mathrm{~cm} image is real inverted and magnified)$

$7. What is the difference between astronomical and terrestrial telescopes?$

$12.16. A coin is placed at a focal point of a converging lens. Is an image formed? What is its nature?$

$12.1. An object 10.0 \mathrm{~cm} in front of a convex mirror forms an image 5.0 \mathrm{~cm} behind the mirror. What is the focal length of the mirror?Ans.$

$12.2. Describe the following terms used in reflection:(i) normal (ii) angle of incidence (iii) angle of reflection$

$x. The critical angle for a beam of light passing from water into air is 48.8 degrees. This means that all light rays with an angle of incidence greater than this angle will be(a) absorbed(b) totally reflected(c) partially reflected and partially transmitted(d) totally transmitted$