A photographic print is found satisfactory when the exposure was for 16 s at a distance of 20 m from a 25-watts lamp. At what distance must the same p
A photographic print is found satisfactory when the exposure was for 16 s at a distance of 20 m from a 25-watts lamp. At what distance must the same paper be held from a 50-watts lamp in order that an exposure of 25 a may give the same result?
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