Question

1) How far apart are an object and an image formed by a 77.9cm focal length converging lens if the image is 2.53x larger than the object and is real?

2)A 31.0cm focal length converging lens is 21.6cm behind a diverging lens. Parallel light strikes the diverging lens. After passing through the converging lens, the light is again parallel. What is the focal length of the diverging lens?

Answer 1

magnification = distance of the image / distance of the object

2.53 = v / u ---------(1)

by lens equation

1 / f = 1 / u + 1 / v

1 / 77.9 = 1 / u + 1 / v -------------(2)

on solving 1 and 2 we'll get

u = 108.691 cm

v = 274.987 cm

since the image is real the object and image will be at opposite directions of the lens

distance between image and object = 108.691 + 274.987

distance between image and object = 383.678 cm

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