Velocity of sound is greater in solids than liquids and gases. It increases with increasing temperature, pressure, and humidity in gases. Stationary waves are produced in organ pipes and stretched strings. Open organ pipes allow all harmonics, while closed pipes allow only odd harmonics. End correction accounts for the pipe diameter. Velocity in strings increases with square root of tension. Interference of waves produces maxima and minima intensities, with the ratio of max to min intensity increasing with amplitude ratio.

1. WAVES AND SOUND

2. Velocity of sound in
Solid
V = √
𝒀
𝜹
Liquid
V = √
𝑩
𝜹
Gas
V = √
ϒ𝑷
𝜹
= √
ϒ𝑹𝑻
𝑴

3. 1) Velocity of sound is greater in
a) oxygen
b) nitrogen
c) Steel
d) Equal in all
Ans: c
2) The velocity of sound in water is 1400m/s. The density of water is 1000kg/m3. Bulk modulus of elasticity of
water is
a) 5 x 1011
b) 1.96 x 109
c) 5 x 1012
d) 5 x 1013
Ans: b

4. Gas
V = √
ϒ𝑷
𝜹
= √
ϒ𝑹𝑻
𝑴
P = 2P v = v
T = 2T v = √ 2 v
M = 2M v =
𝑣
√2

5. 1) The ratio of velocity of sound in hydrogen to oxygen is
a) 4:1
b) 8:1
c) 16:1
d) 32:1
Ans: a
2) At what temperature, the speed of sound in air will become double of its value at 270C?
a) 9270C
b) 3270C
c) 6270C
d) 540C
Ans: a

6. 3) When the temperature increases, velocity of sound in air
a) Increases
b) Decreases
c) Neither decreases nor increases
d) None of above
Ans: a
4) Velocity of humid air is ……. than dry air
a) Less
b) More
c) Neither less nor more
d) None of above
Ans: b

7. 5) When pressure of gas is doubled, velocity of sound becomes
a) Doubled
b) Tripled
c) Unchanged
d) None of above
Ans:

8. Gas
According to newton, sound travels isothermally
V = √
𝑷
𝜹
Laplace correction = sound travels adiabatically
V = √
ϒ𝑷
𝜹
So, isothermal modulus of elasticity = 𝑷
adiabatic modulus of elasticity = ϒ𝑷

9. 1) Isothermal modulus of elasticity is
a) P
b) ϒ𝑃
c) 3P
d) None of above
Ans: a
2) Adiabatic modulus of elasticity is
a) P
b) ϒ𝑃
c) 3P
d) None of above
Ans: b

10. 3) The Laplace’s correction in the expression for velocity of sound given by Newton
is needed because sound waves
a) Are longitudinal
b) Propagate adiabatically
c) Propagate isothermally
d) Are of long wavelength
Ans: b
4) Sound waves are travelling in a medium whose adiabatic elasticity is E1 and
isothermal elasticity of E2. The velocity of sound is proportional to
a) E1
b) E2
c) √ E1
d) √ E2
Ans: c

11. 1) A change in temperature affects which property of sound?
a) Frequency
b) Amplitude
c) Wavelength
d) Sound waves
Ans: c

12. SUPERPOSITION OF WAVES

13. BEATS
Number of beats = f1 – f2
When two tuning forks are sounded together, only one sound is produced, which is called as beat

14. 1) Two tuning forks have frequency of 50Hz and 52Hz. The number of beats produced is
a) 1 Hz
b) 2 Hz
c) 3 Hz
d) 4 Hz
Ans: b
2) Two tuning forks have frequency 440Hz and 444Hz, then resultant frequency is
a) 442 Hz
b) 884 Hz
c) 4 Hz
d) 444 Hz

15. 3) Two tuning forks of frequencies 252Hz and 256Hz are sounded simultaneously, the number of beats heard
per second are
a) 4
b) ¼
c) 2
d) 254
Ans: a
4) When two tuning forks of frequency 484Hz and 486Hz are sounded together, what will be beat frequency?
a) 4 Hz
b) 2 Hz
c) 3 Hz
d) 6 Hz
Ans: b

16. Frequency of tuning fork decreases if it is loaded
increases if it is filed
@ I = I

17. 1) Two tuning fork A and B sounded together to produce 5 beats. The
frequency of B is 512Hz. When fork A is filed and sounded together, the
beat frequency increases. The frequency of A is
a) 502 Hz
b) 512Hz
c) 517Hz
d) 500Hz
Ans: c

18. 2) A tuning fork A of frequency 200Hz is sounded with fork B, the
number of beats per second is 5. By putting some wax on A, the
number of beats increases to 8. The frequency of fork B is
a) 200Hz
b) 195Hz
c) 192Hz
d) 205Hz
Ans: d

19. 3) A tuning fork (A) of unknown frequency gives 4beats/sec when
sounded with another fork B of frequency 256Hz. The fork A is now
loaded with a piece of wax and again 4 beat/sec are heard. Then the
frequency of fork A is
a) 252 Hz
b) 256 Hz
c) 260 Hz
d) 264 Hz
Ans: c

20. 1) The phenomenon of beats is due to
a) Superposition of incoherent waves
b) Superposition of coherent waves
c) Reflection
d) Refraction
Ans: b

21. INTENSITY OF WAVES
I 𝛼 a2
Amax = a1 + a2
Amin = a1 – a2
So,
𝐼𝑚𝑎𝑥
𝐼𝑚𝑖𝑛
=

22. 1) Two waves have amplitude in the ratio of 1:2 Then the ratio of their intensity is
a) 1:2
b) 1:4
c) 1:8
d) 1:16
Ans: b
2) Two waves have amplitude in the ratio of 1:2 Then the ratio of their maximum
intensity to minimum intensity is
a) 9:1
b) 1:4
c) 1:8
d) 1:16
Ans: a

23. 3) Two waves have amplitude in the ratio of 1:3 Then the ratio of their maximum intensity to
minimum intensity is
a) 4:1
b) 1:4
c) 1:8
d) 1:16
Ans: b
4) The ratio of intensities of two interfering waves is 4:1, then the ratio of maximum to minimum
intensity is
a) 1:4
b) 9:1
c) 4:1
d) 3:1
Ans: b

24. 5) When two waves of intensities ‘I’ equal to each other beat together
the maxima of the beat is equal to
a) I
b) 2I
c) 3I
d) 4I
Ans: d

25. STATIONARY / STANDING WAVES
WAVES IN ORGAN PIPES AND STRINGS

26. 1) Waves produced in organ pipe (eg. Flute) is
a) Stationary wave
b) Progressive wave
c) Both a and b
d) None of above
Ans: a
2) Waves produced in string (eg. guitar) is
a) Stationary wave
b) Progressive wave
c) Both a and b
d) None of above
Ans: a

27. OPEN ORGAN PIPE
f1:f2:f3 = 1:2:3
i.e. all harmonic are present

28. CLOSED ORGAN PIPE
f1:f2:f3 = 1:3:5
i.e. only odd harmonic are present

29. 1) In open organ pipe
a) All harmonics are present
b) Only odd harmonics are present
c) Only even harmonics are present
d) None of above
Ans: a
2) In closed organ pipe
a) All harmonics are present
b) Only odd harmonics are present
c) Only even harmonics are present
d) None of above
Ans: b

30. END CORRECTION
End correction (e) = 0.3D
Where D is diameter of open or closed organ pipe

31. 3) End correction in an organ pipe is given by
a) 0.3D
b) 0.6r
c) Both a and b
d) None of above
Ans: c
4) End correction in an organ pipe of diameter 1m is
a) 0.3
b) 0.6
c) Both a and b
d) None of above
Ans: a

32. WAVES IN STRETCHED STRING (eg: guitar)
V = √
𝑇
𝜇

33. 1) In a string, if tension is increased by 4 times then the velocity of transverse wave in string
increases by
a) 4 times
b) 2 times
c) 3 times
d) 1 times
Ans: b
2) A transverse wave passes with speed of 3000m/s along a stretched wire. If the tension in the wire
increases 4 times then the velocity of wave will be
a) 1500m/s
b) 3000m/s
c) 6000m/s
d) 9000m/s
Ans: c

34. A closed organ pipe undergoes resonance in two length l1 and l2. Then
V = 2f (l2 – l1 )
End correction (e) =
l2 − 3l1
2

35. 1) If the difference in resonating lengths is 31.5cm in resonance
column. The wavelength produced is
a) 31.5cm
b) 63cm
c) 49cm
d) 101.5cm
Ans: b

36. 1) Timber of music depends upon
a) Pitch
b) Intensity
c) Number of overtones
d) Number of scales
Ans: c
2) A group of notes which is integral multiple of fundamental note is called
a) Note
b) Harmonics
c) Beats
d) Doppler
Ans: b

37. 1) The intensity of sound gets reduced by 10% on passing through a block. If it
passes through two such blocks, then intensity of the outgoing sound is
a) 19%
b) 91%
c) 81%
d) 18%
Ans: c
2) Angle between particle and wave velocity in transverse wave is
a) 𝜋
b) 0
c) 𝜋/2
d) 2𝜋
Ans: c

38. 1) A closed organ pipe and an open organ pipe have their first
overtone identical in frequency. Their lengths are in the ratio
a) 1:2
b) 2:3
c) 3:4
d) 4:5
Ans: c

39. THANKYOU