Study guide H C Verma JEE Physics Ch. 16 SOUND WAVES

JEE syllabus

Vibration of air columns;Resonance; Beats; Speed of sound in gases; Doppler effect (in sound).
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Sections of the chapter

1 The nature and propagation of sound waves
2. Displacement wave and pressure wave
3. Speed of a sound wave in a material medium
4. Speed of sound in a gas
5. Effect of pressure, temperature and humidity on the speed of sound in air
6. Intensity of sound waves
7. Appearance of sound to human ear
8. Interference of sound waves
9. Standing longitudinal waves and vibrations of air columns
10. Determination of speed of sound in air
11. Beats
12. Diffraction
13 Doppler effect
14. Sonic booms
15. Musical scale
16. Accoustics of buildings
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Study Plan

Day 1

1 The nature and propagation of sound waves
Ex. 16.1
2. Displacement wave and pressure wave
Ex. 16.2
Worked out examples 1, 2

Day 2

3. Speed of a sound wave in a material medium
4. Speed of sound in a gas
5. Effect of pressure, temperature and humidity on the speed of sound in air

Day 3
6. Intensity of sound waves
7. Appearance of sound to human ear
WOE 3 to 5

Day 4
8. Interference of sound waves
9. Standing longitudinal waves and vibrations of air columns

Day 5
10. Determination of speed of sound in air
11. Beats

Day 6
12. Diffraction
13 Doppler effect
14. Sonic booms

Day 7
15. Musical scale
16. Accoustics of buildings

Day 8
WOE 6 to 15

Day 9
WOE 16 to 23

Day 10
Exercises 1 to 10

Day 11
Exercises 11 to 16

Day 12
Exercises 17 to 22

Day 13
Exercises 23 to 28

Day 14
Exercises 29 to 34

Day 15
Exercises 35 to 40

Day 16
Exercises 41 to 46

Day 17
Exercises 47 to 52

Day 18
Exercises 53 to 58

Day 19
Exercises 59 to 64

Day 20
Exercises 65 to 72

special task 73 to 89
Objective I and II
Questions for short answer

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concepts covered

16.11. Beats

The phenomenon of periodic variation of intensity of sound when two sound waves of slighlty different frequencies interfere, is called beats.

16.12
Bending of waves from an obstacle or an opening is called diffraction.

Diffraction effects are appreciable when the dimensions of openings or the obstacles are comparable or smaller than the wave length of the wave.

16.13 Doppler effect
If the source of sound or the observed or both, move with respect to the medium, the frequency observed may be different from the frequency of the source. This apparent change in frequency of the wave due to motion of the source or the observeer is called Doppler effect.

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Audiovisual lecture

Lesson 45: Sound Waves and Doppler Shift
www.curriki.org/nroc/Introductory_Physics_2/lesson45/Container.html













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JEE Question 2007 Paper II

In the experiment to determine the speed of sound using a resonance column,

(A) prongs of the tuning fork are kept in a vertical plane
(B) prongs of the tuning fork are kept in a horizontal plane
(C) in one of the two resonances observed, the length of the resonating air column is close to the wavelength of sound in air
(D) in one of the two resonance observed, the length of the resonating air column is close to half of the wavelength of sound in air

Correct Choice: A
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JEE Question 2007 Paper II

Two trains A and B are moving with speeds 20 m/s and 30 m/s respectively in the same direction on the same straight track, with B ahead of A. The engines are at the front ends. The engine of train A blows a long whistle.

Assume that the sound of the whistle is composed of components varying in frequency from f1 = 800 Hz to f2 = 1120 Hz. The spread in the frequency (highest frequency - lowest frequency) is thus 320 Hz. The speed of sound in still air is 340 m/s.

1. The speed of sound of the whistle is
(A) 340 m/s for passengers in A and 310 m/s for passengers in B
(B) 360 m/s for passengers in A and 310 m/s for passengers in B
(C) 310 m/s for passengers in A and 360 m/s for passengers in B
(D) 340 m/s for passengers in both the trains

Solution: D

Speed of sound is not affected by motion of source or observer. It depends only on the medium and its state of motion w.r.t. the reference frame used.

2. The spread of frequency as observed by the passengers in train B is
(A) 310 Hz
(B) 330 Hz
(C) 350 Hz
(D) 290 Hz

Solution: A

f' = f-0(340-30)/(340-20) = f-0*31/32

∆f' = 31/32∆f-0 = (31/32)*320 = 310 Hz
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