CBSE Class 11 Physics Waves MCQs Set D

Question. The equation of a spherical progressive wave is
(a) y = a sin ϖt
(b) y = a sin (ϖt – kr)
(c) y = a/√2 sin (ϖt – kr)
(d) y = a/r sin (ϖt – kr)
Answer: d

Question. A string is stretched between two fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. The lowest resonant frequency for this string is :
(a) 205 Hz
(b) 10.5 Hz
(c) 105 Hz
(d) 155 Hz
Answer: c

Question. Shock waves are produced by objects
(a) carrying electric charge and vibrating
(b) vibrating with frequency greater than 20000 Hz
(c) vibrating with very large amplitude
(d) moving with a speed greater than that of sound in the medium
Answer: d

Question. Two tones of frequencies n₁ and n₂ are sounded together. The beats can be heard distinctly when
(a) 10 < (n₁ – n₂) < 20
(b) 5 < (n₁ – n₂) > 20
(c) 5 < (n₁ – n₂) < 20
(d) 0 < (n₁ – n₂) < 10
Answer: d

Question. An organ pipe open at one end is vibrating in first overtone and is in resonance with another pipe open at both ends and vibrating in third harmonic. The ratio of length of two pipes is
(a) 1 : 2
(b) 4 : 1
(c) 8 : 3
(d) 3 : 8
Answer: a

Question. When a sound wave of frequency 300 Hz passes through a medium, the maximum displacement of a particle of the medium is 0.1 cm. The maximum velocity of the particle is equal to
(a) 60p cms^–1
(b) 30p cms^–1
(c) 30 cms^–1 30 cms^-1
(d) 60 cms^–1
Answer: a

Question. A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15ms–¹. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is : (Take velocity of sound in air = 330 ms^–1)
(a) 765 Hz
(b) 800 Hz
(c) 838 Hz
(b) 885 Hz
Answer: c

Question. A tuning fork of freqqency 512 Hz makes 4 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per sec when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was
(a) 510 Hz
(b) 514 Hz
(c) 516 Hz
(d) 508 Hz
Answer: d

Question. A person standing symmetrically between two cliffs claps his hands and starts hearing a series of echoes at intervals of 1 sec. If speed of sound in air is 340 m/s, the distance between the parallel cliffs must be
(a) 340 m
(b) 680 m
(c) 1020 m
(d) 170 m
Answer: a

Question. A train has just completed U-curve in a track which is a semicircle. The engine is at the forward end of the semi-circular part of the track while the last carriage is at the rear end of the semi circular track. The driver blows a whistle of frequency 200 Hz. Velocity of sound is 340 m/sec Then the apparent frequency as observed by a passenger in the middle of the train, when the speed of the train is 30 m/sec is
(a) 181 Hz
(b) 200 Hz
(c) 188 Hz
(d) 210 Hz
Answer: b

Question. In a resonance column, first and second resonance are obtained at depths 22.7 cm and 70.2 cm. The third resonance will be obtained at a depth
(a) 117.7 cm
(b) 92.9 cm
(c) 115.5 cm
(d) 113.5 cm
Answer: a

Question. A fork of frequency 256 Hz resonates with a closed organ pipe of length 25.4 cm. If the length of pipe be increased by 2 mm, the number of beats/sec. will be
(a) 4
(b) 1
(c) 2
(d) 3
Answer: c

Question. A whistle of frequency 1000 Hz is sounded on a car travelling towards a cliff with velocity of 18 m s^–1 normal to the cliff. If c = 330 m s^–1, then the apparent frequency of the echo as heard by the car driver is nearly
(a) 1115 Hz
(b) 115 Hz
(c) 67 Hz
(d) 47.2 Hz
Answer: a

Question. Sound waves are travelling in a medium whose adiabatic elasticity is E and isothermal elasticity E’. The velocity of sound waves is proportional to
(a) E’
(b) √E
(c) √E’
(d) E/E’
Answer: b

Question. Two sinusoidal plane waves of same frequency having intensities I0 and 4 I0 are travelling in the same direction. The resultant intensity at a point at which waves meet with a phase difference of zero radian is
(a) I0
(b) 5 I0
(c) 9 I0
(d) 3 I0
Answer: c

Question. An engine running at speed v/10 sounds a whistle of frequency 600 Hz. A passenger in a train coming from the opposite side at speed v/15 experiences this whistle to be of frequency f. If v is speed of sound in air and there is no wind, f is near to
(a) 710 Hz
(b) 630 Hz
(c) 580 Hz
(d) 510 Hz
Answer: a

Question. The property of a medium necessary for wave propagation is
(a) inertia
(b) elasticity
(c) low resistance
(d) All of the above
Answer: d

Question. Two identical piano wires kept under the same tension T have a fundamental frequency of 600 Hz. The fractional increase in the tension of one of the wires which will lead to occurrence of 6 beats/s when both the wires oscillate together would be
(a) 0.02
(b) 0.03
(c) 0.04
(d) 0.01
Answer: a

Question. Velocity of sound waves in air is 330 m/s. For a particular sound wave in air, a path difference of 40 cm is equivalent to phase difference of 1.6p. The frequency of this wave is
(a) 165 Hz
(b) 150 Hz
(c) 660 Hz
(d) 330 Hz
Answer: c

Question. Two periodic waves of intensities I₁ and I₂ pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is
(a) 2 (I₁ + I₂)
(b) I₁ + I₂
(c) (√I₁ + √I² )²
(d) ( √I₁ – √I² )²
Answer: d

Question. An organ pipe P₁ closed at one end vibrating in its first overtone and another pipe P₂ open at both ends vibrating in third overtone are in resonance with a given tuning fork. The ratio of the length of P₁ to that of P₂ is
(a) 8/3
(b) 3/8
(c) 1/2
(d) 1/3
Answer: b

Question. If the intensities of two interfering waves be I₁ and I₂, the contrast between maximum and minimum intensity is maximum, when
(a) I₁ > > I₂
(b) I₁ << I₂
(c) I₁ = I₂
(d) either I₁ or I₂ is zero
Answer: c

Question. A car is moving towards a high cliff. The car driver sounds a horn of frequency f. The reflected sound heard by the driver has as frequency 2f. If v be the velocity of sound, then the velocity of the car, in the same velocity units, will be
(a) v /2
(b) v /√2
(c) v /3
(d) v /4
Answer: c

Question. With 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: b

Question. Sound waves are not transmitted to long distances because,
(a) they are absorbed by the atmosphere
(b) they have constant frequency
(c) the height of antenna required, should be very high
(d) velocity of sound waves is very less
Answer: a

Question. Sound waves of wavelength λ travelling in a medium with a speed of v m/ s enter into another medium where its speed in 2v m/s. Wavelength of sound waves in the second medium is
(a) λ
(b) λ/2
(c) 2λ
(d) 4λ
Answer: c

Question. If we study the vibration of a pipe open at both ends, then which of the following statements is not true ?
(a) Odd harmonics of the fundamental frequency will be generated
(b) All harmonics of the fundamental frequency will be generated
(c) Pressure change will be maximum at both ends 
(d) Antinode will be at open end
Answer: c

Question. An open and closed organ pipe have the same length. The ratio of pth mode of frequency of vibration of two pipes is
(a) 1
(b) p
(c) p (2p + 1)
(d) 2p (2p – 1)
Answer: d

Question. Two sound waves of equal intensity I produce beats. The maximum intensity of sound produced in beats will be
(a) I
(b) 2I
(c) 3I
(d) 4I
Answer: d

Question. A sonometer wire of length l vibrates in fundamental mode when excited by a tuning fork of frequency 416 Hz. If the length is doubled keeping other things same, the string will
(a) vibrate with a frequency of 416 Hz
(b) vibrate with a frequency of 208 Hz
(c) vibrate with a frequency of 832 Hz
(d) stop vibrating
Answer: a

Question. Where should the two bridges be set in a 110cm long wire so that it is divided into three parts and the ratio of the frequencies are 3 : 2 : 1 ?
(a) 20cm from one end and 60cm from other end
(b) 30cm from one end and 70cm from other end
(c) 10cm from one end and 50cm from other end
(d) 50cm from one end and 40cm from other end
Answer: a

Question. Doppler’s effect is not applicable for
(a) audio waves
(b) electromagnetic waves
(c) shock waves
(d) None of these
Answer: c

Question. Sound waves of length l travelling with velocity v in a medium enter into another medium in which their velocity is 4 v. The wavelength in 2nd medium is
(a) 4λ
(b) λ
(c) λ/4
(d) 16 λ
Answer: a

Question. What is the effect of increase in temperature on the frequency of sound produced by an organ pipe?
(a) increases
(b) decreases
(c) no effect
(d) erratic change
Answer: a

Question. 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 vacuum
Answer: c

Question. A source of sound produces waves of wavelength 60 cm when it is stationary. If the speed of sound in air is 320 m s^–1 and source moves with speed 20 m s^–1, the wavelength of sound in the forward direction will be nearest to
(a) 56 cm
(b) 60 cm
(c) 64 cm
(d) 68 cm
Answer: a

Question. Two sources P and Q produce notes of frequency 660 Hz each. A listener moves from P to Q with a speed of 1 ms^–1. If the speed of sound is 330 m/s, then the number of beats heard by the listener per second will be 
(a) zero
(b) 4
(c) 8
(d) 2
Answer: b

Question. The number of possible natural oscillation of air column in a pipe closed at one end of length 85 cm whose frequencies lie below 1250 Hz are : (velocity of sound = 340 ms^–1)
(a) 4
(b) 5
(c) 7
(d) 6
Answer: d

Question. The fundamental frequency of an open organ pipe is 300 Hz. The first overtone of this pipe has same frequency as first overtone of a closed organ pipe. If speed of sound is 330 m/s, then the length of closed organ pipe is
(a) 41 cm
(b) 37 cm
(c) 31 cm
(d) 80 cm
Answer: a 

Question. The speed of sound in a medium depends on
(a) the elastic property but not on the inertia property
(b) the inertia property but not on the elastic property
(c) the elastic property as well as the inertia property
(d) neither the elastic property nor the inertia property
Answer: c

Question. 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: a

Question. If the ratio of maximum to minimum intensity in beats is 49, then the ratio of amplitudes of two progressive wave trains is
(a) 7 : 1
(b) 4 : 3
(c) 49 : 1
(d) 16 : 9
Answer: b

Question. An echo repeats two syllables. If the velocity of sound is 330 m/s, then the distance of the reflecting surface is
(a) 66.0 m
(b) 33.0 m
(c) 99.0 m
(d) 16.5 m
Answer: a

Question. There are three sources of sound of equal intensities and frequencies 400, 401 and 402 vibrations per second. The number of beats/sec is
(a) 0
(b) 1
(c) 3
(d) 2
Answer: b

Question. A wave y = a sin (ϖt – kx) on a string meets with another wave producing a node at x = 0. Then the equation of the unknown wave is
(a) y = a sin (ϖt + kx)
(b) y = –a sin (ϖt + kx)
(c) y = a sin (ϖt – kx)
(d) y = –a sin (ϖt – kx
Answer: b

Question. A wave disturbance in a medium is described by y (x,t) = 0.02 cos (50πt + π/2) cos (10πx) where x and are in metre and t is in second. Which of the following is correct?
(a) A node occurs at x = 0.15 m
(b) An antinode occurs at x = 0.3 m
(c) The speed wave is 5 ms^–1
(d) The wavelength is 0.3 m
Answer: c

Question. The equation y = A sin² (kx -ϖt) represents a wave with
(a) amplitude A, frequency ϖ/ 2π
(b) amplitude A/2, frequency ϖ/ π
(c) amplitude 2A, frequency ϖ/ 4π
(d) it does not represent a wave motion
Answer: b

Question. If two waves of same frequency and same amplitude, on superposition, produce a resultant disturbance of the same amplitude, the wave differ in phase by
(a) π
(b) 2 π/3
(c) Zero
(d) π/3
Answer: b

Question. A pipe closed at one end produces a fundamental note of 412 Hz. It is cut into two pieces of equal length. the fundamental frequencies produced by the two pieces are
(a) 206 Hz, 412 Hz
(b) 824 Hz, 1648 Hz
(c) 412 Hz, 824 Hz
(d) 206 Hz, 824 Hz
Answer: b

Question. Two strings A and B, made of same material, are stretched by same tension. The radius of string A is double of radius of B. A transverse wave travels on A with speed v_A and on B with speed v_B. The ratio v_A / v_B is
(a) 1/2
(b) 2
(c) 1/4
(d) 4
Answer: a

Question. A transverse wave is represented by y = A sin (ϖt – kx). For what value of the wavelength is the wave velocity equal to the maximum particle velocity?
(a) πA/2
(b) π A
(c) 2πA
(d) A
Answer: c

Question. Which of the following changes at an antinode in a stationary wave?
(a) Density only
(b) Pressure only
(c) Both pressure and density
(d) Neither pressure nor density
Answer: d

Question. A fork of unknown frequency gives four beats/sec when sounded with another of frequency 256. The fork is now loaded with a piece of wax and again four beats/sec are heard. Then the frequency of the unknown fork is
(a) 256 Hz
(b) 252 Hz
(c) 264 Hz
(d) 260 Hz
Answer: d

Question. In expressing sound intensity, we take 10^–12 W m^–2 as the reference level. For ordinary conversation, the intensity level is about 10^–6 W m^–2. Expressed in decibel, this is
(a) 10⁶
(b) 6
(c) 60
(d) loge (10⁶)
Answer: c

Question. Frequencies of sound produced from an organ pipe open at both ends are
(a) only fundamental note
(b) only even harmonics
(c) only odd harmonics
(d) even and odd harmonics
Answer: d

Question. The speed of sound in oxygen (O₂) at a certain temperature is 460 ms^–1. The speed of sound in helium (He) at the same temperature will be (assume both gases to be ideal)
(a) 460 ms^–1
(b) 500 ms^–1
(c) 650 ms^–1
(d) 330 ms^–1
Answer: a

Question. Three transverse waves are represented by
y₁ = A cos (kx – ϖt)
y₂ = A cos (kx + ϖt)
y₃ = Acos (ky – ϖt)
The combination of waves which can produce stationary waves is
(a) y₁ and y₂
(b) y₂ and y₃
(c) y₁ and y₃
(d) y₁, y₂ and y₃
Answer: a

Question. Consider the three waves z₁, z₂ and z₃ as
z₁ = A sin (kx – ϖt)
z₂ = A sin (kx +ϖt)
z₃ = A sin (ky – ϖt)
Which of the following represents a standing wave?
(a) z₁ + z₂
(b) z₂ + z₃
(c) z₃ + z₁
(d) z₁ + z₂ + z₃
Answer: a

Question. Each of the properties of sound listed in column A primarily depends on one of the quantitites in column B. Choose the matching pairs from two columns
Column A Column B
Pitch Waveform
Quality Frequency
Loudness Intensity
(a) Pitch-wave form; Quality-frequency; Loudnessintensity
(b) Pitch-frequency; Quality-wave form; Loudnessintensity
(c) Pitch-intensity; Quality-wave form; Loudnessfrequency
(d) Pitch-wave form; Quality-intensity; Loudnessfrequency
Answer: b