Two concave lenses, each with f = -12 cm , are separated by 4.3 cm . An object i

Question

Two concave lenses, each with f = -12 cm , are separated by 4.3 cm . An object is placed 24 cm in front of one of the lenses.

Find the location of the final image produced by this lens combination.

A. in front of the lens closest to the object

B. beyond the lens farest to the object

C. between the two lenses

What's the distance either in front of the lens closest to the object, beyond the lens farest to the object, or between the two lenses depending on your answer in Part 1 ?

Find the magnification of the final image produced by this lens combination.

Explanation / Answer

for first lens,

Using lens equation,

1/f = 1/i + 1/o

1/(-12) = (1/i) + (1/24)

i = 8 cm to the left of first lens.

now this image will work as object for 2nd lens,

so o' = 8 + 4.3 = 12.3 cm

now using lens again,

1/(-12) = (1/12.3) + 1/i

i' = 6.07 cm to the left of 2nd les

image will be formed to the left of both lenses.

Ans (A)

distance from front lens d = 6.07 - 4.3 = 1.77 cm

m1 = 8/24 and m2 = 6.07/12.3

m = m1 x m2 = 0.16

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