Question 1

Paper 2Medium9 marks

Two loudspeakers, S1S_1 and S2S_2 are connected to the same signal generator and emit sound in phase. Figure 1 shows measured distances from each loudspeaker to three positions on a detector’s path. The path lengths are measured to the nearest 0.01 m0.01\ \text{m}

S2S1RQPS2R = 1.54 mS2Q = 1.70 mS2P = 2.18 mS1R = 0.34 mS1Q = 0.80 mS1P = 1.58 m
(a)

Explain why the sources must be coherent for the maxima and minima of the interference pattern to remain in fixed positions.

[2]
(b)

P and Q are consecutive positions of maximum intensity.

(i)

Using Figure 1, calculate the path difference at P and at Q.

[2]
(ii)

Determine the wavelength of the sound.

[2]
(c)

Determine the order nn of constructive interference at R. Show your reasoning.

[3]

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