Question

A concave lens has focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed.​

Answer 1

Answer:

1/f = 1/v-1/u

1/(-20) - 1/-15= - 1/u

(15-20)/300 = - 1/u

1/u = - 5/300

u = - 60 cm

hi/ho= v/u

hi/5 = -15/-60

hi=5/4 cm=1.25 cm

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