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The size of the image of an object, which is at infinity, as formed by a convex lens of focal length 30cm is 2 cm. If a concave lens of focal length 20 cm is placed between the convax lens and the image at a distance of 26 cm from the convex lens, calculate the new size of the image. |
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Answer» `1.25 cm` `I_(1)` actsas virtual objectfor concavelens. Concavelens FORMS the image of`I_(1)` at `I_(2)`.  Lens formula: `1/V - 1/u = 1/f` For concave lens, `1/v - (1)/(4) = - (1)/20` or `1/v = -(1)/(20) + 1/4 = 4/20 = 1/5` or `v = 5 cm` = Distance of `I_(2)`from concavelens. `:. "Magnification" = v/u = ("size of image")/("size ofobject") = 5/4` `:. ("size of image")/(2) = 1.25` `:.` size of image due to concave lens `= 2.5 cm` |
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