JEE Physics Quiz Sound Waves MCQ

When sound wave is refracted from air to water, which of the following will remain unchanged?

1. wave number
2. wavelength
3. wave velocity
4. frequency

A piece of cork is floating on water in a small tank. The cork oscillates up and down vertically when small ripples pass over the surface of water. The velocity of the ripples being 0.21 ms^–1, wave length 15 mm and amplitude 5 mm, the maximum velocity of the piece of cork is (π =22/7 )

1. 0.44 ms^–1
2. 0.24 ms^–1
3. 2.4 ms^–1
4. 4.4 ms^–1

The frequency of a man’s voice is 300 Hz and its wavelength is 1 meter. If the wavelength of a child’s voice is 1.5 m, then the frequency of the child’s voice is:

1. 200 Hz
2. 150 Hz
3. 400 Hz
4. 350 Hz

A machine gun is mounted on an armored car moving with a speed of 20 ms^–1. The gun can point against the direction of motion of car. The muzzle speed of bullet is equal to speed of sound in air i.e., 340 ms^–1. The time difference between bullet actually reaching and sound of firing reaching at a target 544 m away from car at the instant of firing is

1. 1.2 s
2. 0.1 s
3. 1 s
4. 10 s

The ratio of speed of sound in a monoatomic gas to that in water vapours at any temperature is. (when molecular weight of gas is 40 gm/mol and for water vapours is 18 gm/mol)

1. 0.75
2. 0.73
3. 0.68
4. None of these

Under similar conditions of temperature and pressure, In which of the following gases the velocity of sound will be largest.

1. H₂
2. N₂
3. He
4. CO2

If v_rms = root mean square speed of molecules
v_av = average speed of molecules
v_mp = most probable speed of molecules
v_s = speed of sound in a gas
Then, identify the correct relation between these speeds.

1. v_rms > v_av > v_mp > v_s
2. v_av > v_mp > v_rms > v_s
3. v_mp > v_av > v_rms > v_s
4. v_rms > v_av > v_s > v_mp

A sound of intensity I is greater by 3.0103 dB from another sound of intensity 10 nW cm^–2. The absolute value of intensity of sound level  in Wm^–2 is :

1. 2.5 × 10^–4
2. 2 × 10^–4
3. 2.0 × 10^–2
4. 2.5 × 10^–2

For a sound source of intensity I W/m², corresponding sound level is B₀ decibel. If the intensity is increased to 4I, new sound level becomes approximately :

1. 2B₀dB
2. (B₀ + 3)dB
3. (B₀ + 6)dB
4. 4B₀ dB

The sound intensity is 0.008 W/m² at a distance of 10 m from an isotropic point source of sound. The power of the source is approximately :

1. 2.5 watt
2. 0.8 watt
3. 8 watt
4. 10 watt

What happens when a sound wave interferes with another wave of same frequency and constant phase difference ?

1. Energy is gained
2. Energy is lost
3. Redistribution of energy occurs changing with time
4. Redistribution of energy occurs not changing with time

Sound waves from a tuning fork F reach a point P by two separate routes FAP and FBP (when FBP is greater than FAP by 12 cm there is silence at P). If the difference is 24 cm the sound becomes maximum at P but at 36 cm there is silence again and so on. If velocity of sound in air is 330 ms^-1>, the least frequency of tuning fork is :

1. 1537 Hz
2. 1735 Hz
3. 1400 Hz
4. 1375 Hz

Sound signal is sent through a composite tube as shown in the figure. The radius of the semicircular portion of the tube is r. Speed of sound in air is v. The source of sound is capable of giving varied frequencies in the range of v¹ and v² (where v² > v¹). If n is an integer then frequency for maximum intensity is given by :

1. nv/r
2. nv/r(π-2)
3. nv/πr
4. nv/(r-2)π

An interference is observed due to two coherent sources ‘A’ & ‘B’ separated by a distance 4λ along the y-axis where λ is the wavelength of the source. A detector D is moved on the positive x-axis. The number of points on the xaxis excluding the points, x = 0 & x = ∞ at which maximum will be observed is –

1. three
2. four
3. two
4. infinite

A person is talking in a small room and the sound intensity level is 60 dB everywhere within the room. If there are eight people talking simultaneously in the room, what is the sound intensity level ?

1. 60 dB
2. 69 dB
3. 74 dB
4. 81 dB

When a sound wave is reflected from a wall, the phase difference between the reflected and incident pressure wave is:

1. 0
2. π
3. π/2
4. π/4

If λ¹, λ², λ³ are the wavelengths of the waves giving resonance in the fundamental, first and second overtone modes respectively in a open organ pipe, then the ratio of the wavelengths λ¹ : λ² : λ³, is :

1. 1 : 2 : 3
2. 1 : 3 : 5
3. 1 : 1/2 : 1/3
4. 1/3 : 1/5

The maximum variation of pressure in an open organ pipe of length l vibrating in fundamental mode is at.

1. ends
2. middle of pipe
3. L/4 from centre
4. 3L/8 from centre

The fundamental frequency of a closed organ pipe is same as the first overtone frequency of an open pipe. If the length of open pipe is 50 cm, the length of closed pipe is

1. 25 cm
2. 12.5 cm
3. 100 cm
4. 200 cm

Two identical tubes A and B are kept in air and water respectively as shown. If the fundamental frequency of A is f₀, then the fundamental frequency of B is

1. f₀/4
2. f₀/2
3. f₀
4. 2f₀

A tube of diameter d and of length l unit is open at both the ends. Its fundamental frequency of resonance is found to be v₁. The velocity of sound in air is 330 m/sec. One end of tube is now closed. The lowest frequency of resonance of tube is now v₂. Taking into consideration the end correction, v₂/v₁ is

1. (l + 0.6d)/(l + 0.3d)
2. 1(l + 0.3d)/2(l + 0.6d)
3. 1(l + 0.6d)/2(l + 0.3d)
4. 1(d + 0.3l)/2(d + 0.6l)

The second overtone of an open pipe A and a closed pipe B have the same frequencies. The ratio of fundamental frequency of A to the fundamental frequency of B is:

1. 3 : 5
2. 5 : 3
3. 5 : 6
4. 6 : 5

A resonance tube is resonated with tuning fork of frequency 256 Hz. If the length of first and second resonating air columns are 32 cm and 100 cm, then end correction will be

1. 1 cm
2. 2 cm
3. 4 cm
4. 6 cm

A sound source of frequency 512 Hz is producing 6 beats with a guitar. If the string of guitar is stretched slightly then beat frequency decreases. The original frequency of guitar is

1. 506 Hz
2. 512 Hz
3. 518 Hz
4. 524 Hz

The number of beats heard per second if there are three sources of sound of frequencies (n – 1), n and (n + 1) of equal intensities sounded together is :

1. 2
2. 1
3. 4
4. 3

A closed organ pipe and an open pipe of same length produce 4 beats when they are set into vibrations simultaneously. If the length of each of them were twice their initial lengths, the number of beats produced will be [Assume same mode of vibration in both cases]

1. 2
2. 4
3. 1
4. 8

Which of the following does not affect the apparent frequency in doppler effect ?

1. Speed of source
2. Speed of observer
3. Frequency of source
4. Distance between source and observer

An engine driver moving towards a wall with velocity of 50 ms^-1 emits a note of frequency 1.2 kHz. The frequency of note after reflection from the wall as heard by the engine driver when speed of sound in air is 350 ms^-1 is :

1. 1 kHz
2. 1.8 kHz
3. 1.6 kHz
4. 1.2 kHz

An observer moves on a circle as shown in fig. and a small sound source is at S. Let at v₁,v₂,v₃ be the frequencies heard when the observer is at A, B, and C respectively.

1. v₁ > v₂ > v₃
2. v₁ = v₂ > v₃
3. v₂ > v₃ > v₁
4. v₁ > v₃ > v₂

Two factories are sounding their sirens at 400 Hz each. A man walks from one factory towards the other at a speed of 2 m/s. the speed of sound is 320 m/s. The number of beats heard per second by the man is.

1. 6
2. 5
3. 2.5
4. 7.5