Question

how far should an object be placed from a convex lens of focal length 20 cm to obtain its image at a distance of 30 cm from the lens?what will be the hight of the image if the object is 6 cm tall

Answer 1

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f = 20 cm  , v = 30 cm

Using the lens formula,

1/f =1/v - 1/u

1/20 = 1/30 - 1/u

On solving we get,

u = -60 cm 

m = v/u = hi/ho

-30/60 = hi/6

 hi = -3 cm

-ve sign shows that the image is inverted. 

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