Question

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 π. The difference of resultant intensities, at the point A and B, will be_______I.

Answer 1

$I_A = (\sqrt{I_1} + \sqrt{I_2})^2 = 25I$
$I_B = (\sqrt{I_1} - \sqrt{I_2})^2 = I$
So,$I_A - I_B = 25I - I$
$= 24I$
So, the answer is 24.