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An object is placed in front of a concave mirror of focal length 20 cm. The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror. |
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Answer» Solution :m = + 3 and m = - 3, f = - 20cm When, m = 3 `m = - (v)/(u) = 3` v = - 3 u From mirror equation, `(1)/(f) = (1)/(v) + (1)/(u)` `(1)/(-20) = (1)/(-3u) + (1)/(u)` `=(1)/(u)[-(1)/(3)+1]` `(1)/(-20) = (2)/(3u)` `u = - (40)/(3) CM` When, `m =- 3 rArr v = 3u` `(1)/(f) = (1)/(v) + (1)/(u)` `(1)/(-20) = (1)/(3u) + (1)/(u)` `(1)/(-20) = (4)/(3u)` `u = - (4 xx 20)/(3)` ` u = - (80)/(3) cm` |
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