why a pencil dipped in water appears bent at the interface
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https://www.meritnation.com/ask-answer/question/why-does-a-pencil-immersed-in-water-apper-bent-and-short-ex/science/1776928
https://www.meritnation.com/ask-answer/question/why-does-a-pencil-immersed-in-water-apper-bent-and-short-ex/science/1776928