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20cm and -20cm focus length of two lenses forms a equivalent lens what is its power? |
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Answer» Two key facts:1.The power of a lens is the reciprocal of the focal length in meters.2. Powers are additive. The lens with a focal length of +20 cm has a power of 1/0.2 = +5 The lens with a focal length of -20 cm has a power of 1/(-0.2) = - 5 The two lenses together have a power of 5 - 5 = 0 |
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