Physics and illuminations
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Physics and illuminations

[From: ] [author: ] [Date: 11-05-10] [Hit: ]
so the distance has been increased by a factor of 4 ........
A lamp is moved from 15cm to 60cm above the pages of a book. Compare the illumination on the book before and after the lamp is moved. I don't understand this, please explain to me how you've achieved your answer, thanks :)

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The intensity of light decreases as the distance increases ..
the intensity is inversely proportional to the distance squared ..

so the distance has been increased by a factor of 4 ..
the light intensity has decreased by a factor of 4² = 16
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