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![[Post New]](/templates/default/images/icon_minipost_new.gif) 5 Mar 2008 16:49:23 IST
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derivation for lens makerformula, mirror formula in NCERT has been done by assuming u to be negative but again while solving questions we take u -ve isn't it a mistake ?
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5 Mar 2008 17:29:36 IST
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aree yaar if u is negative in the derivation with a particular assumption ...
then if any que gives u in tyhe direction opp to that what was assumed in derivation,,,,,
obviously then u have to take u negative only......
it is not in all the questions.....
reconsider them....
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5 Mar 2008 17:48:18 IST
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in the formula 1/v + 1/u = 1/f, the distances v,u and f are positive. However, when we derived the formula, we derived it using a negative u. Hence, it was necessary to add another -ve sign to make the formula more generalised.
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