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CBSE Class 12-science Answered

a convex lens of focal length f produces a virtual image m times the size of the object .the focus will have magnification equal to-                                                                                                                                                  .  
Asked by Nidhi | 20 Dec, 2014, 02:20: PM
answered-by-expert Expert Answer
Let 'u' be the object distance, 'v' be the image distance and 'f' be the focal length of the lens.
We know that magnification m = v/ u
Given that v = mu
According to lens formula :

begin mathsize 14px style 1 over straight f equals 1 over straight v minus 1 over straight u Here space the space lens space forms space virtual space image space hence space both space straight u space and space straight v space will space be space negative. rightwards double arrow 1 over straight f equals fraction numerator 1 over denominator minus straight v end fraction plus 1 over straight u but space straight v space equals mu Substituting space we space get : 1 over straight f equals fraction numerator 1 over denominator minus mu end fraction plus 1 over straight u 1 over straight f equals 1 over straight u minus 1 over mu space equals fraction numerator straight m minus 1 over denominator mu end fraction rightwards double arrow 1 over straight f equals fraction numerator straight m minus 1 over denominator mu end fraction bold i bold. bold e bold. bold space bold f bold space bold equals bold space open parentheses fraction numerator bold m over denominator bold m bold minus bold 1 end fraction close parentheses bold u bold space bold or bold space bold u bold space bold equals open parentheses fraction numerator bold m bold minus bold 1 over denominator bold m end fraction close parentheses bold space bold f end style
Answered by Jyothi Nair | 21 Dec, 2014, 03:46: PM

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