A) An object is placed 17.5 cm to the left of a converging lens that has a focal

Question

A) An object is placed 17.5 cm to the left of a converging lens that has a focal length f1 = +10.3 cm. How far is the image from the lens? (Give your answer to at least one decimal place.)

B) A screen is placed 42.5 cm to the right of the converging lens. A diverging lens is placed between the converging lens and the screen. When the diverging lens is 14.7 cm to the right of the converging lens the image formed by the lens combination is located at the screen. What is the focal length f2 of the diverging lens?

Explanation / Answer

A)

here , focal length , f1 = 10.3 cm

object distance , do1 = 17.5 cm

Using lens formula ,

1/f1 = 1/do1 + 1/di1

1/10.3 = 1/17.5 + 1/di1

solving for di1

di1 = 25.04 cm

B) Now, for the second lens ,

object distance , do2 = 14.7 - 25.04

do2 = - 10.34 cm

image distance , di2 = 42.5 - 14.7

di2 = 27.8 cm

using lens formula

1/f2 = - 1/10.34 + 1/27.8

f2 = -16.5 cm

the focal length of second lens is -16.5 cm

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