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Title: power of light Post by: adelinetohyj on Jul 23, 2014 A 100 W light bulb is 20% efficient (i.e. 80% of its output is invisible infra-red
radiation and only 20% is visible light). A person can see the light with the naked eye from a distance of 10 km on a dark night. If the area of the pupil of the persons eye is 0.50 cm2, what power of the visible light is received by the eye of the person? (A) 2.4×10−16 W (B) 8.0×10−13 W (C) 1.5×10−12 W (D) 2.0×10−9 W (E) 8.0×10−9 W Title: Re: power of light Post by: bio_man on Aug 4, 2014 (B) 8.0×10−13 W |