multiple lens question

[theonlytycrane]

I believe I know how multiple lenses can work together, but is the KA question below confusing in terms of wording or is it just me? No object distance is given 🙁

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[wheatthinners]

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[NextStepTutor_2]

I believe I know how multiple lenses can work together, but is the KA question below confusing in terms of wording or is it just me? No object distance is given 🙁

View attachment 202169

Hi @theonlytycrane . Yu do not need numbers, only an understanding of how the lenses work. This is a classic example of combining lenses that counteract each-other. In order to cancel each other out or result in a net diverging or converging effect, you need to examine the relative strengths of the lenses. Since they tell you his vision is unchanged with the combination, we want the effects to cancel each other out. Here the image formed by the first lens serves as the object for the 2nd lens. That is why the value is negative.


THIS GUY has a great set of short videos on lens combinations using simple ray diagrams (which you should know for the MCAT). In combination with your lens makers equations, these Qs can be pretty easy points with practice. This Khan passage does almost the exact same scenario, which will allow you to work through it again.


hope this helps, good luck!

 

[theonlytycrane]

I think there might be an error to this question because based on the answer if the image from the first lens (diverging) is at the focal length of the second lens (converging), wouldn't there be no image?