Page 41 - Q & A STPM 2022 Physics

Physics Semester 3 STPM Chapter 21 Sound Waves
Answer: D
Refer to the answer in Question 2. On the same axes, sketch the y-x graph and
p-x graph (see figure below). From the shape of the p in the graph, it can be
deduced that the expression for p is p = –p 0 cos (ωt – kx).

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y = y sin (ωt – kx)
0
p
0
Distance, x

21.2 Sources of Sound

Section A Multiple-choice Questions

Question 1
Which of the following is the equation for a standing wave?
A y = A sin 5t C y = A cos (5t + 2x)
B y = A sin (5t – 2x) D y = A cos 2x sin 5t

Answer: D
Exam Tips
Exam Tips
Amplitude of standing wave varies with distance x. In A, B and C the amplitude
is constant, A. In D, amplitude = A cos 2x, varies with x.

Question 2
A standing wave set up in a string fixed at both ends has three nodes. If the
frequency of the wave is doubled, how many nodes are there?
A 4 C 6
B 5 D 7

Answer: B
The wavelength is halved when the frequency is doubled. Semester

N N N
3
N N N N N

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021 STPM Q&A Physics T3.indd 401 17/02/2022 10:24 AM