Sound Waves PYQs Set 6 (PDF)

Set 6 of 9 · Questions 151-180 of 268

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Mere Teacher · Previous Year Questions JEE Main Physics · Sound Waves · Set 6 (Q151-180)
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151. $Two stationary sources each emitting waves of wavelength λ, an observer moves from one source to another with velocity u . Then number of beats heard by him$ (1) $\frac{2 u}{λ}$ (2) $\frac{u}{λ}$ (3) $uλ$ (4) $\frac{u}{2 λ}$ 152. $Sound waves of frequency 600 Hz fall normally on a perfectly reflecting wall. The shortest distance from the wall at which all particles will have maximum amplitude of vibration is (speed of sound = 300 m s^{- 1})$ (1) $\frac{1}{4} m$ (2) $\frac{1}{8} m$ (3) $\frac{3}{8} m$ (4) $\frac{7}{8} m$ 153. $There is one closed pipe whose third overtone is in resonance with the upper string, which is in the 4^{th} overtones with an open pipe, then$ (1) $2 n = 3 m$ (2) $5 n = 7 m$ (3) $3 n = 5 m$ (4) $7 n = 5 m$ 154. $A point source is kept at the center of a spherically enclosed detector. If the volume of the detector increased by 8 times, the intensity will$ (1) $increase by 64 times$ (2) $increase by 8 times$ (3) $decrease by 4 times$ (4) $decrease by 8 times$ 155. $A pipe open at both ends has fundamental frequency f in air. The pipe is dipped vertically in water so that half of it is in water. The fundamental frequency of the air column is now:$ (1) $\frac{3 f}{4}$ (2) $2 f$ (3) $f$ (4) $\frac{f}{2}$ 156. $Wire having tension 225 N produces six beats per second when it is tuned with a fork. When tension changes to 256 N, it is tuned with the same fork, the number of beats remain unchanged. The frequency of the fork will be$ (1) $186 Hz$ (2) $225 Hz$ (3) $256 Hz$ (4) $280 Hz$ 157. $A sound absorber attenuates the sound level by 20 dB. The intensity decreases by a factor of:$ (1) $1000$ (2) $10000$ (3) $10$ (4) $100$ 158. $A sound wave of frequency 245 Hz travelswith the speed of 300 ms^{- 1} along the positive x - axis. Each point of the wave moves to and for through a total distance of 6 cm . What will be the mathematical expression of this travelling wave?$ (1) $Y (x, t) = 0.03 (sin 5.1 x - (0.2 \times 10^{3}) t)$ (2) $Y (x, t) = 0.06 (sin 5.1 x - (1.5 \times 10^{3}) t)$ (3) $Y (x, t) = 0.06 (sin 0.8 x - (0.5 \times 10^{3}) t)$ (4) $Y (x, t) = 0.03 (sin 5.1 x - (1.5 \times 10^{3}) t)$ 159. $The fundamental frequency in an open organ pipe is equal to the third harmonic of a closed organ pipe. If the length of the closed organ pipe is 20 cm, the length of the open organ pipe is$ (1) $13.3 cm$ (2) $16 cm$ (3) $12.5 cm$ (4) $8 cm$ 160. $Two sound sources S_{1} and S_{2} of frequencies 324 Hz and 320 Hz are placed at certain separation. An observer is moving away from S_{1} and towards S_{2} on line joining them. If he hears no beats then speed of observer is (v = 344 m/sec):$ (1) $20 m/s$ (2) $10 m/s$ (3) $5 m/s$ (4) $2.1 m/s$ 161. $The transverse displacement y(x,t) of a wave on a string is given by y (x, t) = e^{- (a x^{2} + b t^{2} + 2 ab xt)} This represents a:$ (1) $wave moving in +x-direction with speed \frac{a}{b}$ (2) $wave moving in -x-direction with speed \frac{b}{a}$ (3) $standing wave of frequency b$ (4) $standing wave of frequency \frac{1}{b}$ 162. $A cylindrical tube, open at both ends has fundamental frequency f in air. The tube is dipped vertically in water, so that half of it is in water. The fundamental frequency ofair column is now$ (1) $f /2$ (2) $3 f /4$ (3) $2 f$ (4) $f$ 163. $An open pipe and a closed pipe are in resonance with each other with their first overtones. The ratio of their lengths our$ (1) $4 : 3$ (2) $3 : 4$ (3) $1 : 3$ (4) $3 : 5$ 164. $A student is performing the experiment of Resonance Column. The diameter of the column tube is 4cm. The distance frequency of the tuning fork is 512 Hz. The air temperature is 38°C in which the speed of sound is 336 m/s. The zero of the meter scale coincides with the top end of the Resonance column. When first resonance occurs, the reading of the water level in the column is$ (1) $14.0$ (2) $15.2$ (3) $16.4$ (4) $17.6$ 165. $In the case of sound waves, wind is blowing from source to receiver with speed U_{W} . Both source and receiver are stationary. If λ_{0} is the original wavelength with no wind and V is speed of sound in air then wavelength as received by the receiver is given by:$ (1) $λ_{0}$ (2) $V+UwV λ_{0}$ (3) $V-UwV λ_{0}$ (4) $VV+Vw λ_{0}$ 166. $A man is watching two trains, one leaving and the other coming in with equal speeds of 4 m/sec. If they sound their whistles, each of frequency 240 Hz, the number of beats heard by the man (velocity of sound in air = 320 m/sec) will be equal to$ (1) $6$ (2) $3$ (3) $0$ (4) $12$ 167. $A sound source is moving towards a stationary observer with 1/10 of the speed of sound. The ratio of apparent to real frequency is$ (1) $10/9$ (2) $11/10$ (3) $(11/10)^{2}$ (4) $(9/10)^{2}$ 168. $The correct figure that shows, schematically, the wave pattern produced by superposition of two waves of frequencies 9 Hz and 11 Hz is:$ (1) (2) (3) (4) 169. $A police car horn emits a sound at a frequency 240 Hz. when the car is at rest. If the speed of the sound is 330 m/s the frequency heard by an observer who is approaching the car at a speed of 11 m/s, is:$ (1) $248 Hz$ (2) $244 Hz$ (3) $240 Hz$ (4) $230 Hz$ 170. $Which of the following does not affect the apparent frequency in doppler effect?$ (1) $Speed of source$ (2) $Speed of observer$ (3) $Frequency of source$ (4) $Distance between source and observer$ 171. $A train moving with 20 m/s towards a stationary observer produces frequency of 440 Hz. The apparent frequency heard will be (v = 330 m/s)$ (1) $448 Hz$ (2) $455 Hz$ (3) $440 Hz$ (4) $468 Hz$ 172. $The pressure wave P = 0.01 sin [1000 t - 3 x] Nm^{- 2} corresponds to the sound produced by a vibrating blade on a day when atmospheric temperature is 0^{\circ} C . On some other day when temperature is T the speed of sound produced by the same blade and at the same frequency is found to be 336 ms^{- 1} . Approximate value of T is:$ (1) $4^{\circ} C$ (2) $11^{\circ} C$ (3) $12^{\circ} C$ (4) $15^{\circ} C$ 173. $A source of sound of frequency 450 cycles/sec is moving towards a stationary observer with 34 m/sec speed. If the speed of sound is 340 m/sec, then the apparent frequency will be$ (1) $410 cycles/sec$ (2) $500 cycles/sec$ (3) $550 cycles/sec$ (4) $450 cycles/sec$ 174. $While measuring the speed of sound by performing a resonance column experiment, a student gets the first resonance condition at a column length of 18 cm during winter. Repeating the same experiment during summer, she measures the column length to be x cm for the second resonance. Then$ (1) $x > 54$ (2) $54 > x > 36$ (3) $36 > x > 18$ (4) $18 > x$ 175. $Intensity level of sound whose intensity is 10^{- 8} Wm^{- 2} is ... dB$ (1) $8$ (2) $4$ (3) $40$ (4) $80$ 176. $A plane sound wave travelling with velocity v in a medium A reaches a point on the interface of medium A and medium B . If velocity of sound in medium B is 2 v, the angle of incidence for total internal reflection of the wave will be greater than (sin 30^{\circ} = 0.5) and sin 90^{\circ} = 1)$ (1) $15^{\circ}$ (2) $30^{\circ}$ (3) $45^{\circ}$ (4) $90^{\circ}$ 177. $In an experiment to measure the speed of sound by a resonating air column, a tuning fork of frequency 500 Hz is used. The length of the air column is varied by changing the level of water in the resonance tube. Two successive resonances are heard at air columns of length 50.7 cm and 83.9 cm. Which of the following statements is (are) true?$ (1) $The speed of sound determined from this experiment is 332 m s^{-1}$ (2) $The end correction in this experiment is 0.9 cm$ (3) $The wavelength of the sound wave is 66.4 cm$ (4) $The resonance at 50.7 cm corresponds to the fundamental harmonic$ 178. $When a car is approaching the observer, the frequency of horn is 100Hz. After passing the observer, it is 50Hz. If the observer moves with the car, the frequency will be \frac{x}{3} Hz where x =___$ 179. $In an experiment to determine the velocity of sound in air at room temperature using a resonance is observed when the air column has a length of 20.0 cm for a tuning fork of frequency 400 Hz is used. The velocity of the sound at room temperature is 336 m s^{- 1} . The third resonance is observed when the air column has a length of____cm.$ 180. $A tuning fork resonates with a sonometer wire of length 1 m stretched with a tension of 6 N . When the tension in the wire is changed to 54 N, the same tuning fork produces 12 beats per second with it. The frequency of the tuning fork is \dots\dots\dots. Hz .$