- #1

fluidistic

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## Homework Statement

A bi-concave lens (n=1.5) has radii of 20 cm and 10cm and a thickness of 5 cm. Describe the image of an object of 2.5 cm of hight and situated at 8 cm from the first side of the lens.

Attempt:

[tex]\frac{1}{f}=(n-1) \left [ \frac{1}{R_1}-\frac{1}{R_2} + \frac{(n-1)d}{nR_1R_2} \right ][/tex]. After some arithmetics, [tex]f=-\frac{4}{3}[/tex].

So I know that the image is on the same side of the oject and according to my sketch is it smaller. I'm having a hart time figuring out how to calculate its distance from the lens.

I've been searching on the Internet but there are very few information for thick lens or I'm just blind that I don't find anything that could help me.

Once I have the place of the image, I can easily calculate the magnification and hence say how hight is the image. But I'm stuck as how to calculate the distance between the image and the lens.

Thanks for any help.