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Question
Sir, i'm having problem wit the sign conventions (for r1 & r2) related to the lens makers formula. Can you please help me explain which of the radii(r1 or r2) should be positiv or negative for various lens(plane convex, plano concave, biconvex,)

Answer
If you're looking at a biconvex lens, for example, coming from the left, the first surface has a center of curvature to the right, so r1 is positive.  The second surface has a center of curvature to the left so r2 is negative.  For a plane, or plano surface, r = infinity so 1/r is zero.  

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Richard J. Raridon

Expertise

I can answer most questions in undergraduate physics courses, including electricity and magnetism, atomic and nuclear, mechanics and optics.

Experience

I have taught undergraduate physics courses

Organizations
Sigma Xi, AAAS, SE section of APS

Education/Credentials
BA in math, MA in physics, PhD in physical chemistry

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Fellow of AAAS

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