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Difference of resultant intensities at phase differences pi/2 and pi for sources of intensity I and 9I

The same question, asked 2 times: 21 Apr 2025 S1, 14 May 2026 S2. Every wording below, oldest first.

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  1. Question 1

    21 Apr 2025 S1

    13
    Interference fringes are produced on the screen by using two light sources of intensities I and 9I. The phase difference between the beams is π/2\pi/2 at point PP and π\pi at point Q on the screen. The difference between the resultant intensities at points P and Q is (cos⁡90∘=0,cos⁡π=−1)\left( \cos90^{\circ}= 0,\cos\pi= - 1 \right)

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  2. Question 2

    14 May 2026 S2

    143
    Interference fringes are produced on a screen by using two light sources of intensities I and 9I. The phase difference between the beams is π2\dfrac{\pi}{2}, at point P and π\pi at point Q on the screen. The difference between the resultant intensities at points P and Q is (cos⁡π2=0,cos⁡π=−1)\left(\cos\dfrac{\pi}{2} = 0, \cos\pi = -1\right)

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