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The magnification of an object placed it front of a convex lens of focal length `20cm` is `+2`. To obtain a magnification of `-2` , the object will has to be moved a distance equal toA. `10 cm`B. `20 cm`C. `30 cm`D. `40cm` |
Answer» Correct Answer - B When magnification is `+2`. `u=-x` `v=-2x` `f=+20` Using `(1)/(-2x)+(1)/(x)=(1)/(20)` or `x=10cm` To have a magnificatio of `-2` `u=-y` `v=+2y` and `f=+20` `:. (1)/(2y)+(1)/(y)=(1)/(20)` or `y=30cm` `:. y-x=20cm` |
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