NCERT Solutions for class 11 Physics | Chapter 15 - Waves

Questions
1 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 all the particles are oscillating with the same amplitude
D there are some particles which are always at rest

Answer:A, B, C, D
2 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 10 m/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

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3 The transverse displacement of a string 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
4 During propagation of a plane progressive mechanical wave
A all the particles are vibrating in the same phase
B amplitude of all the particles is equal
C particles of the medium executes SHM
D wave velocity depends upon the nature of the medium

Answer:B, C, D
5 Speed of sound waves in a fluid depends upon
A directly on the density of the medium
B square of bulk modulus of the medium
C inversely on the square root of density
D directly on the square root of bulk modulus of the medium

Answer:C, D
6 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 1.5 m and its mass is 3.0 × 10-2kg.
A it represents a progressive wave of frequency 60 Hz
B it represents a stationary wave of frequency 60 Hz
C it is the result of the superposition of two waves of wavelength 3 m, frequency 60 Hz each travelling with a speed of 180 m/s in the opposite direction
D amplitude of this wave is constant

Answer:B, C
7 A transverse harmonic wave on a string is described by y (x,t) = 3.0 sin (36t + 0.018x + π/4) where x and y are in cm and t is in s. The positive direction of x is from left to right
A the wave is travelling from right to left
B the speed of the wave is 20 m/s
C frequency of the wave is 5.7 Hz
D the least distance between two successive crests in the wave is 2.5 cm

Answer:A, B, C
8 A string of mass 2.5 kg is under a tension of 200 N. The length of the stretched string is 20.0 m. If the transverse jerk is struck at one end of the string, the disturbance will reach the other end in
A one second
B 0.5 second
C 2 seconds
D data given is insufficient

Answer:0.5 second
9 Equation of a plane progressive wave is given by y = 0.6 sin 2π(t-x/2). On reflection from a denser medium, its amplitude becomes 2/3 of the amplitude of the incident wave
A y = 0.6 sin 2π(t+x/2)
B y = -0.4 sin 2π(t+x/2)
C y = 0.4 sin 2π(t+x/2)
D y = -0.4 sin 2π(t-x/2)

Answer:y = -0.4 sin 2π(t+x/2)
10 A sound wave is passing through the air column in the form of compression and rarefaction. In consecutive compressions and rarefactions,
A density remains constant
B Boyle’s law is obeyed
C bulk modulus of air oscillates
D there is no transfer of heat

Answer:there is no transfer of heat
11 Which of the following statements are true for wave motion?
A mechanical transverse waves can propagate through all mediums
B longitudinal waves can propagate through solids only
C mechanical transverse waves can propagate through solids only
D longitudinal waves can propagate through a vacuum

Answer:mechanical transverse waves can propagate through solids only
12 With the propagation of longitudinal waves through a medium, the quantity transmitted is
A matter
B energy
C energy and matter
D energy, matter, and momentum

Answer:energy
13 Change in temperature of the medium changes
A frequency of sound waves
B amplitude of sound waves
C wavelength of sound waves
D loudness of sound waves

Answer:wavelength of sound waves
14 Speed of sound wave in air
A is independent of temperature
B increases with pressure
C increases with an increase in humidity
D decreases with an increase in humidity

Answer:increases with an increase in humidity
15 Sound waves of wavelength λ travelling in a medium with a speed of v m/s enter into another medium where its speed is 2v m/s. The wavelength of sound waves in the second medium is
A λ
B λ/2
C 2 λ
D 4 λ

Answer: 2 λ
16 Water waves produced by a motorboat sailing in water are
A neither longitudinal nor transverse
B both longitudinal and transverse
C only longitudinal
D only transverse

Answer:both longitudinal and transverse
17 closed organ pipe (closed at one end) is excited to support the third overtone. It is found that air in the pipe has
A four nodes and four antinodes
B four nodes and three antinodes
C three nodes and four antinodes
D three nodes and three antinodes

Answer:four nodes and four antinodes
18 The fundamental frequency of a closed end organ pipe is n. Its length is doubled and radius is halved. Its frequency will become nearly
A n/2
B n/3
C n
D 2 n

Answer:n/2
19 The fundamental frequency of an organ pipe is 512 Hz. If its length is increased, then frequency will
A decrease
B increase
C remains same
D cannot be predicted

Answer:decrease
20 If vibrations of a string are to be increased by a factor of two, then tension in the string must be made
A twice
B eight times
C half
D four times

Answer:twice

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