(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

An object is located to the left of a thin lens. The image is upright, and the distance between the object and image is 20 cm. What are the focal length and object distance if the lens is 2 times the hieght of the object?

2. Relevant equations

1/p + 1/q = 1/f

3. The attempt at a solution

I actually know how to get the focal length and object distance, I'm just having a bit of difficulty with an initial step.

If the image and object are 20 cm apart. How do I determine what the relationship between them is? I know the image location (q) is negative and the object (p) is positive. According to my book, I should use 20 cm = -q - p. That isn't immediately obvious to me, I would have thought doing something like 20 = p - q or 20 = p + q... can anyone explain why it's -q - p for the distance differential?

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# Homework Help: Thin Lens

Can you offer guidance or do you also need help?

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