1.

20cm and -20cm focus length of two lenses forms a equivalent lens what is its power?

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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