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Question

The size of the image of an object, which is at infinity, as formed by a convex lens of focal length 30 cm is 2 cm. If a concave lens of focal length 20 cm is placed between the convex lens and the image at a distance of 26 cm from the convex lens, calculate the new size of the images.

A
1.25cm
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B
2.5cm
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C
1.05cm
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D
2cm
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Solution

The correct option is A 2.5cmFor the image formed by convex lens in first case,Magnification=vu=30u=2y0When concave lens is placed between the convex lens and image,u=30−26=4Thus 1v′−14=1−20v′=5Total magnification in second case= Magnification by convex lens× Magnification by concave lens=30u×54=yy0Thus y2=54y=2.5cm

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