Sound Waves PYQs Set 8 (PDF)

Set 8 of 8 · Questions 211-236 of 236

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Mere Teacher · Previous Year Questions NEET Physics · Sound Waves · Set 8 (Q211-236)
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211. $When both source and listener are approaching each other the observed frequency of sound is given by (V_{L} and V_{S} is the velocity of listener and source respectively, n_{0} = radiated frequency)$ (1) $n = n_{0} (\frac{V + V _{L}}{V - V _{S}})$ (2) $n = n_{0} (\frac{V - V _{L}}{V + V _{S}})$ (3) $n = n_{0} (\frac{V - V _{L}}{V - V _{S}})$ (4) $n = n_{0} (\frac{V + V _{L}}{V + V _{S}})$ 212. $A speeding motorcyclist sees traffic jam ahead him. He slows down to 36 km hou r^{- 1} . He finds that traffic has eased and a car moving ahead of him at 18 km hou r^{- 1} is honking at a frequency of 1392 Hz. If the speed of sound is 343 m s^{- 1}, the frequency of the honk as heard by him will be$ (1) $1332 Hz$ (2) $1372 Hz$ (3) $1412 Hz$ (4) $1454 Hz$ 213. $A pipe of length 85 cm is closed from one end. Find the number of possible natural oscillations of air column in the pipe whose frequencies lie below 1250 Hz. The velocity of sound in air is 340 m/s.$ (1) $12$ (2) $8$ (3) $6$ (4) $4$ 214. $Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 m s^{- 1} with respect to the ground. If an observer in car A detects a frequency 2000 H z of the sound coming from car B, what is the natural frequency of the sound source in B ? (speed of sound in air = 340 m s^{- 1})$ (1) $2250 Hz$ (2) $2060 Hz$ (3) $2300 Hz$ (4) $2150 Hz$ 215. $A stationary source emits sounds waves of frequency 500 Hz . Two observers moving along a line passing through the source detect sound to be of frequencies 480 Hz and 530 Hz . Their respective speeds are, in ms^{- 1} (Given speed of sound = 300 m / s)$ (1) $12, 16$ (2) $12, 18$ (3) $16, 14$ (4) $8, 18$ 216. $Assume that the displacement (s) of air is proportional to the pressure difference (Δ p) created by a sound wave. Displacement (s) further depends on the speed of sound (v), density of air (ρ) and the frequency (f) . If Δ p \sim 10 Pa, v \sim 300 m / s, ρ \sim 1 kg / m^{3} and f \sim 1000 Hz then s will be of the order of (take the multiplicative constant to be 1)$ (1) $\frac{3}{100} mm$ (2) $10 mm$ (3) $1 mm$ (4) $3 10 mm$ 217. $A resonance tube is old and has jagged end. It is still used in the laboratory to determine velocity of sound in air. A tuning fork of frequency 512 Hz produces first resonance when the tube is filled with water to a mark 11 cm below a reference mark, near the open end of the tube. The experiment is repeated with another fork of frequency 256 Hz which produces first resonance when water reaches a mark 27 cm below the reference mark. The velocity of sound in air, obtained in the experiment, is close to:$ (1) $322 ms^{- 1}$ (2) $341 ms^{- 1}$ (3) $335 ms^{- 1}$ (4) $328 ms^{- 1}$ 218. $A closed organ and an open organ tube are filled by two different gases having same bulk modulus but different densities ρ_{1} and ρ_{2^{’}}, respectively. The frequency of 9^{th} harmonic of closed tube is identical with 4^{th} harmonic of open tube. If the length of the closed tube is 10 cm and the density ratio of the gases is ρ_{1} : ρ_{2} = 1 : 16, then the length of the open tube is:$ (1) $\frac{15}{7} cm$ (2) $\frac{20}{7} cm$ (3) $\frac{15}{9} cm$ (4) $\frac{20}{9} cm$ 219. $A resonance tube is old an has jagged end. It is still used in the laboratory to determine velocity of sound in air. A tuning fork of frequency 512 Hz produces first resonance when the tube is filled with water to mark 11 cm below a reference mark, near the open end of the tube. The experiment is repeated with another fork of frequency 256 Hz which produces first resonance when water reaches a mark 27 cm below the reference mark. The velocity of sound in air, obtained in the experiment, is close to:$ (1) $322 m/ s^{-1}$ (2) $341 m/ s^{-1}$ (3) $328 m/ s^{-1}$ (4) $335 m/ s^{-1}$ 220. $The second overtone of an open organ pipe has the same frequency as the first overtone of a closed pipe L meter long. The length of the open pipe will be$ (1) $4L$ (2) $L$ (3) $2L$ (4) $\frac{L}{2}$ 221. $Two coherent sources of sound, S_{1} and S_{2}, produce sound waves of the same wavelength, λ = 1 m, in phase. S_{1} and S_{2} are placed 1.5 m apart (see fig). A listener, located at L, directly in front of S_{2} finds that the intensity is at a minimum when he is 2 m away from S_{2} . The listener moves away from S_{1}, keeping his distance from S_{2} fixed. The adjacent maximum of intensity is observed when the listener is at a distance d from S_{2} . Then, d is$ (1) $5 m$ (2) $2 m$ (3) $12 m$ (4) $3 m$ 222. $A source of sound emits waves with frequency f Hz and speed V m/sec. Two observers move away from this source in opposite directions each with a speed 0.2 V relative to the source. The ratio of frequencies heard by the two observers will be$ (1) $3 : 2$ (2) $2 : 3$ (3) $1 : 1$ (4) $4 : 10$ 223. $A vibrating string of certain length l under a tension T resonates with a mode corresponding to the first overtone (third harmonic) of an air column of length 75 cm inside a tube closed at one end. The string also generates 4 beats per second when excited along with a tuning fork of frequency n. Now when the tension of the string is slightly increased the number of beats reduces to 2 per second. Assuming the velocity of sound in air to be 340 m/s, the frequency n of the tuning fork in Hz is$ (1) $344$ (2) $336$ (3) $117.3$ (4) $109.3$ 224. $If ' P' is the length of the open pipe, ' r' is the internal radius of the pipe and ' V' is the velocity of sound in air then fundamental frequency of open pipe is$ (1) $\frac{V}{( l + 0.3 r )}$ (2) $\frac{V}{( l + 1.2 r )}$ (3) $\frac{V}{( l + 0.6 r )}$ (4) $\frac{V}{2 ( l + 1.2 r )}$ 225. $The loudness and pitch of a sound note depends on$ (1) $intensity and frequency$ (2) $frequency and number of harmonics$ (3) $intensity and velocity$ (4) $frequency and velocity.$ 226. $Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 340 m/s]:$ (1) $350 Hz$ (2) $361 Hz$ (3) $411 Hz$ (4) $448 Hz$ 227. $If a wave gets refracted into a denser medium, then which of the following is true?$ (1) $wavelength speed and frequency decreases.$ (2) $wavelength increases, speed decreases and frequency remains constant.$ (3) $wavelength and speed decreases but frequency remains constant.$ (4) $wavelength, speed and frequency increases.$ 228. $The Doppler's effect is applicable for$ (1) $Light waves$ (2) $Sound waves$ (3) $Space waves$ (4) $Both (a) and (b)$ 229. $Sound waves transfer$ (1) $only energy not momentum$ (2) $energy$ (3) $momentum$ (4) $both energy and momentum.$ 230. $Which of the following is incorrect?$ (1) $If the wave is longitudinal, it must be a mechanical wave.$ (2) $If the wave is mechanical, it may or may not be transverse wave.$ (3) $Mechanical waves cannot propagate in vacuum.$ (4) $Diffraction helps us to distinguish between sound wave and light wave.$ 231. $The Doppler effect is applicable for$ (1) $Sound waves only$ (2) $Light waves only$ (3) $Both sound and light waves$ (4) $None of these$ 232. $An observer while going on scooter hears sound of two sirens of same frequencies from two opposite directions. If he travels along the direction of one of the siren, then he$ (1) $Listens resonance$ (2) $Listens beats$ (3) $Will not listen sound due to destructive interference$ (4) $Will listen intensive sound due to constructive interference$ 233. $Doppler's effect will not be applicable when the velocity of sound source is$ (1) $Equal to that of the sound velocity$ (2) $Less than the velocity of sound$ (3) $Greater than the velocity of sound$ (4) $Zero$ 234. $The source producing sound and an observer both are moving along the direction of propagation of sound waves. If the respective velocities of sound, source and an observer are v, v_{s} and v_{o}, then the apparent frequency heard by the observer will be (n = frequency of sound)$ (1) $\frac{n ( v + v _{o} )}{v - v _{o}}$ (2) $\frac{n ( v - v _{o} )}{v - v _{s}}$ (3) $\frac{n ( v - v _{o} )}{v + v _{s}}$ (4) $\frac{n ( v + v _{o} )}{v + v _{s}}$ 235. $A small source of sound moves on a circle as shown in fig. and an observer is sitting at O. Let at v_{1}, v_{2}, v_{3} be the frequencies heard when the source is at A, B, and C respectively.$ (1) $v_{1} > v_{2} > v_{3}$ (2) $v_{1} = v_{2} > v_{3}$ (3) $v_{2} > v_{3} > v_{1}$ (4) $v_{1} > v_{3} > v_{2}$ 236. $The waves set up in a closed pipe are$ (1) $longitudinal and progressive$ (2) $longitudinal and stationary$ (3) $transverse and stationary$ (4) $transverse and progressive.$