Page 623 - SUBSEC October 2017_Neat

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Item 23 refers to the following diagram. 25. Which of the following is NOT a condition
necessary for the formation of stationary
waves from two progressive waves?

(A) Progressive waves must be
superimposed.
(B) Progressive waves must be
travelling in opposite directions.
(C) Progressive waves must be of
23. Two wave sources X and Y are positioned as the same amplitude
shown 50 mm and 120 mm from a point P. and frequency.
The two sources produce waves which are (D) The distance between the
in phase and which both have wavelengths sources of progressive waves
of 20 mm. The phase difference between must be a whole number of
the waves arriving at P is wavelengths.

(A) 45 o
(B) 90 o 26. A glass tube of effective length 0.60 m is
(C) 180 o closed at one end. Given that the speed of
(D) 360 o sound in air is 300 ms , the two LOWEST
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resonant frequencies are

24. The magnitude of the threshold of hearing (A) 125 Hz, 250 Hz
at 1 kHz is (B) 125 Hz, 375 Hz
(C) 250 Hz, 375 Hz
(A) 10 -8 Wm -2 (D) 500 Hz, 750 Hz
(B) 10 Wm -2
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(C) 10 Wm -2
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(D) 10 Wm -2
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02138010/CAPE/SPEC/2017