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28. An object of size 7em is placed at 27em in front of a concave mirror of focal lengthi Scm. Where is the sharp image formed? Find the size and nature of the image. Alsofind the magnification |
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Answer» We know that, for a concave mirror the focal length will be negative.Therefore,given: u = -27cm f = -18cm h(object size) = 7cm ( Note that the distance at which you will obtain sharp image will be your "v" i.e. the object distance for that image formation which is required in the question) hence,1/v + 1/u = 1/f(mirror formula)1/v + (1/(-27)) = 1/(-18)1/v = 1/27 + 1/-18 ( LCM of 18 and 27 is 54)1/v = 1/(-54)v = -54cmimage distance = -54cmhence, image is formed on the same side. now we know,h'/h = -v/u(h' denotes object height)h'/7 = -(-54)/-(27)h' = 7 * (-2)h' = -14cm hence, image is inverted (since h' is negative) and it is on the same side of that of the object (since v is negative). |
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