onsider an object with s=12cm that produces an image with s=15cm. Note that when

Question

onsider an object with s=12cm that produces an image with s=15cm. Note that whenever you are working with a physical object, the object distance will be positive (in multiple optics setups, you will encounter "objects" that are actually images, but that is not a possibility in this problem). A positive image distance means that the image is formed on the side of the lens from which the light emerges.What is the object distance? You will need to use the magnification equation to find a relationship between s and s. Then substitute into the thin lens equation to solve for s.

Explanation / Answer

Given that,

s = 12 cm

s' = 15 cm

from lens equation,

1 / f = 1 / s + 1 / s'

1 / f = 1 / 12 + 1/ 15

f = 6.67 cm

magnification m = -s' / s

m = -15 / (12) = -1.125

s' = 1.25s

from equation,

1 / 6.67 = 1 / s + (1 / 1.25s)

s = 12 cm

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