p35_007 - come from the image of the source, a distance d...

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7. The intensity of light from a point source varies as the inverse of the square of the distance from the source. Before the mirror is in place, the intensity at the center of the screen is given by I 0 = A/d 2 , where A is a constant of proportionality. After the mirror is in place, the light that goes directly to the screen contributes intensity I 0 , as before. Reflected light also reaches the screen. This light appears to
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Unformatted text preview: come from the image of the source, a distance d behind the mirror and a distance 3 d from the screen. Its contribution to the intensity at the center of the screen is I r = A (3 d ) 2 = A 9 d 2 = I 9 . The total intensity at the center of the screen is I = I + I r = I + I 9 = 10 9 I . The ratio of the new intensity to the original intensity is I/I = 10 / 9....
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