Two light beams of intensities 4I and 9I interfere on a screen. The phase difference between these beams on the screen at point A is zero and at point B is . The difference of resultant intensities, at the point A and B, will be_________I.

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Vishal Baghel | Contributor-Level 10

6 months ago

$I_{A} = 9 l + 4 l + 2 \sqrt[]{9 l * 4 l} c o s 0 °$

$= 13 l + 12 l = 25 l$

$I_{B} = 9 l + 4 l + 2 \sqrt[]{9 l * 4 l} c o s π$

$= 13 l - 12 l = l$

$∴ I_{A} - I_{B} = 24 l$

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