Title 16. Waves and Sound Hard.pdf ✅

1. The speed of a wave in a certain medium is 960 m/sec. If 3600 waves pass over a certain point of the medium in 1 minute, the wavelength is (a) 2 meters (b) 4 meters (c) 8 meters (d) 16 meters 2. A plane wave is described by the equation       = − − 2 10 4 3 cos  t x y . The maximum velocity of the particles of the medium due to this wave is (a) 30 (b) 3  / 2 (c) 3/4 (d) 40 3. A transverse wave is described by the equation 0 Y = y sin 2        −  x ft The maximum particle velocity is four times the wave velocity if (a) 4 0 y  = (b) 2 0 y  = (c) 0  = y (d) 2 0  = y 4. The equation of a wave travelling in a string can be written as y = 3 cos  (100 t – x) Its wavelength is (a) 100 cm (b) 2 cm (c) 5 cm (d) None of these 5. A plane wave is represented by x = 1.2 sin (314 t + 12.56 y) where x and y are distances measured along in x and y direction in meter and t is time in seconds. This wave has (a) A wave length of 0.25 m and travels m + ve x- direction (b) A wavelength of 0.25 m and travels in + ve y- direction (c) A wavelength of 0.5 m and travels in – ve y-direction (d) A wavelength of 0.5 m and travels in – ve x-direction 6. The equation of displacement of two waves are given as y1 = 10 sin       + 3 3   t ; y2 = 5 [sin 3 t + 3 cos 3t] Then what is the ratio of their amplitudes (a) 1 : 2 (b) 2 : 1 (c) 1 : 1 (d) None of these 7. The equation of a wave travelling on a string is y = 4 sin       − 8 8 2 x t  if x and y are in cm, then velocity of wave is (a) 64 cm/sec in – x direction (b) 32 cm/sec in – x direction (c) 32 cm/sec in +x direction (d) 64 cm/sec in +x direction 8. The equation of wave is y = 2 sin  (0.5x − 200 t) where x and y are expressed in cm and t in sec. The wave velocity is (a) 100 cm/sec (b) 200 cm/sec (c) 300 cm/sec (d) 400 cm/sec 9. The stationary wave produced on a string is represented by the equation y = 5 cos sin (40 ) 3 t x         where x and y are in cm and t is in seconds. The distance between consecutive nodes is (a) 5 cm (b)  cm (c) 3 cm (d) 40 cm 10. On sounding tuning fork A with another tuning fork B of frequency 384 Hz, 6 beats are produced per second. After loading the prongs of A with wax and then sounding it again with B, 4 Beats are produced per second what is the frequency of the tuning fork A (a) 388 Hz (b) 80 Hz (c) 378 Hz (d) 390 Hz 11. Beats are produced with the help of two sound waves on amplitude 3 and 5 units. The ratio of maximum to minimum intensity in the beats is (a) 2 : 1 (b) 5 : 3 (c) 4 : 1 (d) 16 : 1 12. When two sound waves with a phase difference of  / 2 and each having amplitude A and frequency  are superimposed on each other, then the maximum amplitude and frequency of resultant wave is (a) ; / 2 2  A (b) ; 2 A (c) 2A; 2  (d) 2A; 13. There is a destructive interference between the two waves of wavelength  coming from two different paths at a point. To get maximum sound or constructive interference at that point, the path of one wave is to be increased by (a)  / 4 (b)  / 2 (c) 4 3 (d)  14. The tuning fork and sonometer wire were sounded together and produce 4 beats/second when the length of sonometer wire is 95 cm or 100 cm. The frequency of tuning fork is (a) 156 Hz (b) 152 Hz (c) 148 Hz (d) 160 Hz 15. A tuning fork F1 has a frequency of 256 Hz and it is observed to produce 6 beats/second with another tuning fork F2. When F2 is loaded with wax. It still produces 6 beats/second with F1. The frequency of F2 before loading was (a) 253 Hz (b) 262 Hz (c) 250 Hz (d) 259 Hz 16. A source of sound of frequency 90 vibration/sec is approaching a stationary observer with a speed equal to 1/10 the speed of sound. What will be the frequency heard by the observer (a) 80 vibration/sec (b) 90 vibration/sec (c) 100 vibration/sec (d) 120 vibration/sec 17. A source of sound of frequency 500 Hz is moving towards an observer with velocity 30 m/s. The speed of the sound is 330 m/s. The frequency heard by the observer will be
(a) 550 Hz (b) 458.3 Hz (c) 530 Hz (d) 545.5 Hz 18. A motor car blowing a horn of frequency 124 vibration/sec moves with a velocity 72 km/hr towards a tall wall. The frequency of the reflected sound heard by the driver will be (velocity of sound in air is 330 m/s) (a) 109 vibration/sec (b) 132 vibration/sec (c) 140 vibration/sec (d) 248 vibration/sec 19. The driver of car travelling with a speed 30 meter/sec. towards a hill sounds a horn of frequency 600 Hz. If the velocity of sound in air is 330 m/s the frequency of reflected sound as heard by the driver is (a) 720 Hz (b) 555.5 Hz (c) 550 Hz (d) 500 Hz 20. The source of sound s is moving with a velocity 50 m/s towards a stationary observer. The observer measures the frequency of the source as 1000 Hz. What will be the apparent frequency of the source when it is moving away from the observer after crossing him ? The velocity of sound in the medium is 350 m/s (a) 750 Hz (b) 857 Hz (c) 1143 Hz (d) 1333 Hz 21. A source and listener are both moving towards each other with speed v/10 where v is the speed of sound. If the frequency of the note emitted by the source is f, the frequency heard by the listener would be nearly (a) 1.11 f (b) 1.22 f (c) f (d) 1.27 f 22. What should be the height of transmitting antenna if the T.V. telecast is to cover a radius of 128 Km (a) 1560 m (b) 1280 m (c) 1050 m (d) 79 m 23. An electromagnetic radiation has an energy 14.4 KeV. To which region of electromagnetic spectrum does it belong (a) Infra red region (b) Visible region (c) X-rays region (d)  -ray region 24. Two waves travelling along same direction on the same string have equations: y1 = A1sin(t - kx + 1) y2 = A2sin(t - kx + 2) If A1> A2 and φ1> φ2, then according to the principle of superposition, the resultant wave has an amplitude A such that (a) A = A1 + A2 (b) A = A1-A2 (c) A2 ≤ A ≤ A1 (d) A1- A2 ≤ A ≤ A1 + A2 25. A wave on a string passes the point x = 0 with amplitude A0, angular frequency 0 and average rate of energy transfer P0. As the wave travels down the string it gradually loses energy and at the point x = l the average rate of energy transfer becomes 2 P0 . At the point x = £angular frequency and amplitude are respectively: (a) 0 and A0/2 (b) 0/2 and A0 (c) Less than 0 and A0 (d) 0/2and A0/2 26. Graph shows three waves that are separately sent along a string that is stretched under a certain tension along an x-axis. If 1, 2 and 3 are their angular frequencies respectively then: (a) 1 = 3 >2 (b) 1 >2 >3 (c) 2>1 = 3 (d) 1 = 2 = 3 27. A wave pulse is generated in a string that lies along an x-axis. At the points A and B, as shown in figure, if RA and RB are ratio of wave speed to the particle speed respectively then : (a) RA>RB (b) RB>RA (c) RA = RB (d) Information is insufficient to decide. 28. Three waves, all having the same amplitude and wavelength, travel along a string in the same direction. One of the wave has phase constant of 45°. The phase constants of the other waves, if all three together produce fully destructive interference, are: (a) 1800 and 2700 (b) 1350 and 2550 (c) 1650 and 2850 (d) 1800 and 3150 29. A source that is continuously emitting sound at constant frequency, starts moving away from the detector with initial speed 4 m/s, along the line joining them. The acceleration a of the source is opposite to velocity having value 1 m/ s2 . If the motion starts at t = 0 s then frequency as recorded by the detector from t = 0 to t = 8s (a) Remains same (b) First increases then decreases. (c) First decreases then increases (d) Increases for whole duration.
30. In a sound wave, to increase the intensity by a factor of 10, pressure amplitude must be changed by a factor of: (a) 10 (b) 10 (c) 102 (d) 20 31. Figure shown is a graph, at a certain time t, of the displacement function S(x, t) of three sound waves 1,2 and 3 as marked on the curves that travel along an x-axis through air. If p1,p2 and p3 represent their pressure amplitudes respectively, then correct relation between them is : (a) P1> P2> P3 (b) P3> P2> P1 (c) P1 = P2 = P3 (d) P2>P3>P1 32. A sound source of frequency 500 Hz and an observer are moving along their line of motions with speeds 10 m/s and 20 m/s respectively. The frequency of the sound as heard by the observer at the moment as shown in the figure is nearly equal to (speed of sound in air is 340 m/s): (a) 500 Hz (b) 530 Hz (c) 545 Hz (d) 458 Hz 33. A curve is plotted to represent the dependence of the ratio of the received frequency f to the frequency f0emitted by the source on the ratio of the speed of observer Vob to the speed of sound Vsound in a situation in which an observer is moving towards a stationary sound source. The curve is best represented by : (a) (b) (c) (d) 34. Sound waves are emitted uniformly in ali directions from a point source. The dependance of sound level  in decibels on the distance r can be expressed as (a and b are positive constants) (a)  =-b logra (b) =a-b(log r)2 (c) = a - b log r (d) = a – b/r2 35. Air confined to a tube closed at both ends with movable piston at one of the ends is used to produce standing sound waves inside. If V is speed of sound in air inside and L is length of the tube then condition for resonant frequencies vnis: (a) vn= 2L nV , n =1,2,3...... (b) vn= 4L nV ,n = 1,3,5............ (c) vn= 8L nV , n = 1,5,9........... (d) A tube closed at both ends does not have any resonant frequencies 36. A sound source emits two sinusoidal sound waves, both of wavelength X, along paths A and B as shown in figure. The sound travelling along path B is reflected from five surfaces as shown and then merges at point Q exactly out of phase with the sound that travelled along path A. The minimum value of d in terms of is : (a) 8  (b) 4  (c) 8 3 (d) 2  37. The two pipes are submerged in sea water, arranged as shown in figure. Pipe A, with length LA = 1.5 m and one open end, contains a small sound source that sets up the standing wave with the second lowest resonant frequency of that pipe. Sound from the pipe A sets up resonance in pipe B, which has two open ends. The resonance is at the second lowest resonant frequency of the pipe B. The length of the pipe B is: (a) 1m (b) 1.5m (c) 2 m (d) 3 m 38. 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 (a) 2.5 watt (b) 0.8 watt (c) 8 watt (d) 10 watt 39. For a sound sources of intensity 1 W/m2 , corresponding sound level is B0 decibel. If intensity is increased to 4I, new sound level becomes: (a) 2B0Db (b) (B0 + 3)Db (c) (B0 + 6)Db (d) 4B0dB
40. In the case of sound waves, wind is blowing from source to receiver with speed Uw. Both the source and the receiver are stationary. If 0is the original wavelength with no wind and V is speed of sound in air then the wavelength as received by the receiver is given by: (a) 0 (b) 0 w V V U       + (c) 0 w V V U       − (d) 0 V U w V          + 41. There is a set of four tuning forks, one with the lowest frequency vibrating at 550 Hz. By using any two tuning forks at a time, the following beat frequencies are heard: 1,2,3, 5, 7, 8. The possible frequencies of the other three forks are: (a) 552,553,560 (b) 557,558,560 (c) 552,553,558 (d) 551,553, 558 42. An accurate and reliable audio oscillator is used to standardize a tuning fork marked as 512 Hz. When the oscillator reading is 514, two beats are heard per second. When the oscillator reading is 510, the beat frequency is 6 Hz. The frequency of the tuning fork is (a) 506 (b) 510 (c) 516 (d) 158 43. A sound wave of wavelength  travels towards the right horizontally with a velocity V. It strikes and reflects from a vertical plane surface, travelling at a speed v towards the left. The number of positive crests striking in a time interval of three seconds on the wall is (a) 3 (V + v) / (b) 3(V – v)/ (c) (V + v)/ 3 (d) (V – v) /3 44. Two waves represented by y1 = 10 Sin (2000  t) and y2 = 10 sin (2000  t + /2) are superposed at any point at a particular instant. The resultant amplitude is (a) 10 units (b) 20 units (c) 14.1 units (d) Zero 45. When two simple harmonic motions of same periods, same amplitude, having phase of 3/2, and at right angles to each other are super imposed, the resultant wave form is a (a) Circle (b) Parabolac (c) Ellipse (d) Figure of eight 46. A line source emits a cylindrical wave. If the medium absorbs no energy, the amplitude will vary with distance r from the source as proportional to (a) r−1 (b) r−2 (c) r−1/2 (d) r1/2 47. A transverse wave is described by the equation y = y0 sin 2 (ft – x/a). The maximum particle velocity is equal to four times the wave velocity if a is equal to (a wavelength ) (a) y0 / 4 (b) y0/2 (c) y0 (d) 2y0 48. Inside a gas, sound transmission is possible for (a) Longitudinal waves only (b) Transverse waves only (c) Neither longitudinal waves nor transverse waves (d) Both longitudinal and transverse waves 49. A flat horizontal platform moves up and down in S.H.M. with an amplitude of 1 cm. A small object is placed on the platform. What is the maximum frequency the platform can have, if the object is not to separate from it during any part of the motion ? (a) 2 980 per second (b) 980 / 2ππ per second (c) 980 / 2 per second (d) 2  980 per second 50. The amplitude of a wave disturbance propagating in the positive x-direction is given by y =1/ (1 + x2 ) at time t = 0 and by y = 1/[1 + (x – 1)2 at t = 2 seconds, where x and y are in meters. The shape of the wave disturbance does not change during the propagation. The velocity of the wave is (a) 1 ms−1 (b) 0.5 ms−1 (c) 1.5 ms−1 (d) 2 ms−1 51. An accurate and reliable audio oscillator is used to standardize a tuning fork marked as 512 Hz. When the oscillator reading is 514, two beats are heard per second. When the oscillator reading is 510, the beat frequency is 6 Hz. The frequency of the tuning fork is (a) 506 (b) 510 (c) 516 (d) 158 52. A sound wave of wavelength  travels towards the right horizontally with a velocity V. It strikes and reflects from a vertical plane surface, travelling at a speed v towards the left. The number of positive crests striking in a time interval of three seconds on the wall is (a) 3 (V + v) / (b) 3(V – v)/ (c) (V + v)/ 3 (d) (V – v) /3 53. Two waves represented by y1 = 10 Sin (2000  t) and y2 = 10 sin (2000  t + /2) are superposed at any point at a particular instant. The resultant amplitude is (a) 10 units (b) 20 units (c) 14.1 units (d) Zero 54. When two simple harmonic motions of same periods, same amplitude, having phase of 3/2, and at right angles to each other are super imposed, the resultant wave form is a (a) Circle (b) Parabola (c) Ellipse (d) Figure of eight 55. A line source emits a cylindrical wave. If the medium absorbs no energy, the amplitude will vary with distance r from the source as proportional to (a) r−1 (b) r−2 (c) r−1/2 (d) r1/2 56. A transverse wave is described by the equation y = y0 sin 2 (ft – x/a). The maximum particle velocity is equal to four times the wave velocity if a is equal to (a wavelength ) (a) y0 / 4 (b) y0/2 (c) y0 (d) 2y0