document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=666455>Question 666455</A>: <I><SPAN STYLE=\"word-break: break-all;\"> the intensity of light, l, received at a source varies inversely as the square of the the distance, d, from the source. if the light intensity is 79 foot-candles at 30 feet, find the light intensity at 10 feet </SPAN>\n" );
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document.write( "(1) I = c/(d^2), where I is the intensity in foot-candles, c a constant of propotionality and d is the distance in feet.<BR>\n" );
document.write( "First we find c using the known intensity at a known distance or<BR>\n" );
document.write( "(2) I = c/30^2 = 79, giving<BR>\n" );
document.write( "(3) c = 79*900<BR>\n" );
document.write( "To find the intensity at 10 feet use (1) with c of (3) and get<BR>\n" );
document.write( "(4) I at 10' = 79*900/10^2 or<BR>\n" );
document.write( "(5) I at 10' = 79*9 = 711<BR>\n" );
document.write( "Answer: The light intensity at 10' is 711 foot-candles.<BR>\n" );
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