JEE Advanced 2015 · Paper 2 · Physics Q4

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PhysicsInteger+4Question 4 of 60

Four harmonic waves of equal frequencies and equal intensities $I_0$ have phase angles 0, $\pi/3$ , $2\pi/3$ and $\pi$ . When they are superposed, the intensity of the resulting wave is $nI_0$ . The value of $n$ is

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Answer and worked solution

Official answer: 3

Add the phasors. Four equal amplitudes at 0°, 60°, 120° and 180°:
$(1+\tfrac12-\tfrac12-1,\ 0+\tfrac{\sqrt3}2+\tfrac{\sqrt3}2+0)=(0,\sqrt3).$

Intensity. The resultant amplitude is $\sqrt3$ times one wave's, so $I=3I_0$ .

Answer: 3

Topics:Superposition and interference

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JEE Advanced 2015 · Paper 2, Physics question 4