A text book of physics, for the use of students of science and engineering (1918)
Duncan, John, d. 1941, Starling, Sydney George, 1873- · London Macmillan · leaf 570
ill casta shadow. If now a screen be placed at B, of exactly the same sizeand shape as the shadow at B, then on removing A, the light thatoriginally fell on A will fall on B. If the distance SB is twice SA, we ILLUMINATING POWER 545 now from geometry that the area of the screen B is four times… … Fig. 493.—Illustration of the law of inverse squares. -j C is one-ninth of that at A, and so on. In general, since the area: any perpendicular section of the pyramid SABC is proportional tole square of the distance of the section from S, the amount of light■r unit area is inversely as the square of…
Physics
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