NCERT Solutions for class 11 Physics | Chapter 15 - Waves

Questions
1 Which of the following statements is/are correct about the standing wave?

I. In a standing wave the disturbance produce is confined to the region where it is produced.

II. In a standing wave, all the particles cross their mean position together.

III. In a standing wave, energy is transmitted from one region of space to other

A I and II
B Only II
C Only III
D I, II and III

Answer:I and II
2 Which of the following changes at an antinode in a stationary wave?
A Neither pressure nor density
B Both pressure and density
C Pressure only
D Density only

Answer:Neither pressure nor density

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3 The reason for introducing Laplace correction in the expression for the velocity of sound in a gaseous medium is
A no change in the heat of the medium during the propagation of the sound through it
B no change in the temperature of the medium during the propagation of the sound through it
C change in the pressure of the gas due to the compression and rarefaction
D change in the volume of the gas

Answer:no change in the heat of the medium during the propagation of the sound through it
4 The property of a medium necessary for wave propagation is
A All of the above
B Elasticity
C Inertia
D Low resistance

Answer:All of the above
5 What is the effect of humidity on sound waves when humidity increases?
A Speed of sound waves is more
B Speed of sound waves is less
C Speed of sound waves remains same
D Speed of sound waves becomes zero

Answer:Speed of sound waves is more
6 Sound waves transfer
A both energy and momentum
B only energy not momentum
C momentum
D energy

Answer:both energy and momentum
7 The ratio of the speed of a body to the speed of sound is called
A Mach number
B Sonic index
C Doppler ratio
D Refractive index

Answer:Mach number
8 From a point source, if amplitude of waves at a distance r is A, its amplitude at a distance 2r will be
A A/2
B A/4
C 2 A
D A

Answer:A/2
9 Sound travels in rocks in the form of
A both longitudinal and transverse elastic waves
B non-elastic waves
C transverse elastic waves only
D longitudinal elastic waves only

Answer:both longitudinal and transverse elastic waves
10 When a sound wave goes from one medium to another, the quantity that remains unchanged is
A frequency
B wavelength
C amplitude
D speed

Answer:frequency
11 For which of the following do the longitudinal waves exist?
A Both
B Air
C Water
D None of these

Answer:Both
12 The rate of transfer of energy in a wave depends
A directly on the square of the wave amplitude and square of the wave frequency
B directly on the square of the wave amplitude and root of the wave frequency
C directly on the wave amplitude and square of the wave frequency
D None of these

Answer:directly on the square of the wave amplitude and square of the wave frequency
13 Frequencies of sound produced from an organ pipe open at both ends are
A even and odd harmonics
B only odd harmonics
C only even harmonics
D only fundamental note

Answer:even and odd harmonics
14 If there are six loops for 1 m length in transverse mode of Melde’s experiment., the no. of loops in longitudinal mode under otherwise identical conditions would be
A 3
B 6
C 12
D 8

Answer:3
15 The fundamental frequency of a closed organ pipe of length 20 cm is equal to the second overtone of an organ pipe open at both the ends. The length of organ pipe open at both theends is
A 120 cm
B 140 cm
C 80 cm
D 100 cm

Answer: 120 cm
16 What is the effect of increase in temperature on the frequency of sound produced by an organ pipe?
A increases
B no effect
C decreases
D erratic change

Answer:increases
17 Which of the following statements are true for a stationary wave?
A Every particle has a fixed amplitude which is different from the amplitude of its nearest particle.
B All the particles cross their mean position at the same time.
C There is no net transfer of energy across any plane.
D There are some particles which are always at rest.

Answer:A, B, C, D
18 A train, standing in a station yard, blows a whistle of frequency 400 Hz in still air. The wind starts blowing in the direction from the yard to the station with a speed of 10m/s. Given that the speed of sound in still air is 340 m/s,
A the frequency of sound as heard by an observer standing on the platform is 400 Hz.
B the speed of sound for the observer standing on the platform is 350 m/s.
C the frequency of sound as heard by the observer standing on the platform will increase.
D the frequency of sound as heard by the observer standing on the platform will decrease.

Answer:A, B
19 The transverse displacement of a string (clamped at its both ends) is given by y (x,t) = 0.06 sin (2πx/3) cos (120πt). All the points on the string between two consecutive nodes vibrate with
A same frequency
B same phase
C same energy
D different amplitude.

Answer:A, B, D
20 The displacement of a string is given by y (x,t) = 0.06 sin (2πx/3) cos (120πt)

where x and y are in m and t in s. The length of the string is 1.5m and its mass is 3.0 10-2 kg

A It represents a progressive wave of frequency 60Hz.
B It represents a stationary wave of frequency 60Hz.
C It is the result of superposition of two waves of wavelength 3 m, frequency 60Hz each travelling with a speed of 180 m/s in opposite direction.
D Amplitude of this wave is constant.

Answer:B, C

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