Question

Numerical Problems. 1. The focal length of a convex lens is 15 cm. An object is placed 10cm part from the lens. Calculate the image distance.Is the image real or virtual? 2.If an object be placed at a distance of 60cm from a convex lens of a focal length 20 cm , a real image is formed behind the lens. obtain the position of the image and its magnification. 3.A concave lens has focal length of 12cm . At what distance should the object from the lens be placed so that it froms an image at 8cm from the lens? Also find the magnification produced by the lens. 4. An object is placed at a distance of 50 cm from a concave lens of focal length 20cm.Find the position, nature and size of the image. 5.An object is placed 10cm of a lens. The lens from a real image three times magnified. Where is the image formed? What is the focal length of lens?.​

Answer 1

Explanation:

1/focal length = 1/ image distance + 1/ object distance

apply sign convention positive if distance is measured right of lens and negative If measured to left of lens

positive focal length means convex lens and real image

negative focal length means concave lens and virtual image

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