Page 51 - Q & A STPM 2022 Physics

Physics Semester 3 STPM Chapter 21 Sound Waves
1 T
(ii) Fundamental frequency, f 0 =
2L μ

= 1 4.80 Hz
–3
2(2.00) (4.80 × 10 /2.00)
Penerbitan Pelangi Sdn Bhd. All Rights Reserved.
= 35.4 Hz

Three lowest frequencies: f 0 , 2 f 0 , 3 f 0
= 35.4 Hz, 70.8 Hz, 106 Hz

21.3 Intensity Level of Sound

Section A Multiple-choice Questions

Question 1

A sound wave has an intensity of 4.00 μW m . What is the intensity level of
–2
sound?
(Threshold of hearing: 10 W m )
–12
–2
A 25 dB C 66 dB
B 40 dB D 76 dB

Answer: C
I
Intensity level of sound, b = 10 log   dB
I 0
Common Error = 10 log  4.0 × 10 W m –2 dB
–6
–2 
–12
Distinguish the difference 10 W m
between intensity and = 66.0 dB
intensity level.

Question 2

The power output from a sound source emitting a single frequency is doubled.
What is the increase in decibel level?
A 0.50 dB Semester
B 2.0 dB
C 3.0 dB 3
D 4.0 dB

411

021 STPM Q&A Physics T3.indd 411 17/02/2022 10:24 AM