Superposition Standing Waves Beats & Doppler — Practice Questions

Free NEET Physics multiple-choice questions on Superposition Standing Waves Beats & Doppler. Attempt each question and reveal the answer with a full explanation.

An observer moves towards a stationary source of sound with a speed v o . If v is the speed of sound, the apparent frequency f' is related to the actual frequency f by: f' = f(v+v o)/v f' = f v/(v-v o) f' = f(v-v o)/v f' = f v/(v+v o) If the intensity of sound is increased by a factor of 100 , the increase in the sound level in decibels (dB) is: 20 dB 10 dB 100 dB 40 dB In a stationary wave, the energy is: Confined between nodes and not transported Transported from nodes to antinodes Transported in the direction of wave propagation Distributed uniformly throughout the medium Two sound waves having a phase difference of 60 have a path difference of: /6 /3 /2 /12 For destructive interference between two waves, the path difference must be: (2n+1) 2 n n 2 (n+1) A stationary wave is formed in a string of length L fixed at both ends. If the string vibrates in its third harmonic, the distance between two consecutive nodes is: L/3 L/6 2L/3 L/2 Two sound waves are given by y 1 = A (1000 t) and y 2 = A (1008 t) . The number of beats heard per second is: 4 8 1004 2 A sonometer wire of length l vibrates in its fundamental mode. If the radius of the wire is doubled while keeping tension and length constant, the new frequency n' will be: n/2 2n n/4 n A point source emits sound waves in all directions in an isotropic medium. How does the intensity I of the wave vary with the distance r from the source? I 1/r 2 I 1/r I r 2 I is constant When the intensity of sound increases by a factor of 1000 , the increase in the intensity level in decibels (dB) is: 30 dB 3 dB 1000 dB 20 dB Two sound waves of amplitudes A and 3A interfere at a point. The ratio of maximum to minimum intensity in the resulting interference pattern is: 4:1 16:1 9:1 2:1 Two sound sources produce 12 beats in 4 seconds. If the frequency of one source is 250 Hz , the frequency of the other source could be: 253 Hz 250 Hz 244 Hz 262 Hz A sonometer wire of density and radius r is held under tension T . The fundamental frequency is n . If another wire of the same material and same length but radius 2r is held under the same tension, the new fundamental frequency will be: n/2 n/4 2n n In a stationary wave, the distance between two consecutive antinodes is 20 cm . The wavelength of the wave is: 40 cm 20 cm 10 cm 80 cm The ratio of intensities of two waves is 1:16 . The ratio of their amplitudes is: 1:4 1:16 1:256 1:2 In the Doppler effect, if the source is moving away from a stationary observer with a speed equal to the speed of sound, the apparent frequency is: f/2 0 2f f Which of the following properties of a sound wave determines its 'pitch'? Frequency Amplitude Intensity Waveform An observer is moving away from a stationary source of frequency 1000 Hz with a speed of 34 m/s . If the speed of sound is 340 m/s , the frequency heard by the observer is: 900 Hz 1100 Hz 910 Hz 1000 Hz A wave is represented by the equation y = a (kx + t) . This wave is: Traveling in the negative x-direction Traveling in the positive x-direction A stationary wave None of these Two sound waves are represented by y 1 = a ( t - kx) and y 2 = a ( t - kx) . The phase difference between the two waves is: /2 /4 0 In a stationary wave, the distance between a node and the next node is 20 cm . If the frequency of the wave is 400 Hz , the speed of the wave is: 160 m/s 80 m/s 320 m/s 40 m/s The frequency of the fifth harmonic of a string fixed at both ends is 500 Hz . The frequency of the third harmonic is: 300 Hz 100 Hz 1500 Hz 250 Hz In a stationary wave, the phase difference between two points located in the same loop is: 0 /2 2 When a source of frequency f moves towards a stationary observer with speed v s , the apparent frequency is f' . If the source moves away from the observer with the same speed, the apparent frequency is f'' . If v is the speed of sound, the ratio f'/f'' is: v + v s v - v s v - v s v + v s v 2 v 2 - v s 2 v v + v s A source and an observer move away from each other with a velocity of 10 m/s with respect to the ground. If the velocity of sound in air is 340 m/s and the frequency of the source is 660 Hz , the apparent frequency is: 621 Hz 701 Hz 660 Hz 630 Hz A stationary wave is represented by y = 5 ( x 3 ) (40 t) where x and y are in cm and t in seconds. The separation between two adjacent nodes is: 3 cm 6 cm 1.5 cm 4 cm A source of sound of frequency 600 Hz is moving towards a stationary observer with a speed of 30 m/s . If the speed of sound is 330 m/s , the frequency heard by the observer is: 660 Hz 550 Hz 600 Hz 720 Hz Two sound waves with wavelengths 5.0 m and 5.5 m respectively, each propagate in a gas with velocity 330 m/s . We expect the number of beats per second to be: 6 3 12 0 Two tuning forks A and B produce 4 beats/sec. Fork A has a frequency of 256 Hz . When B is loaded with wax, the beat frequency becomes 2 beats/sec. The frequency of B is: 260 Hz 252 Hz 258 Hz 254 Hz A car blowing a horn of frequency f moves towards a stationary observer. As the car passes the observer, the frequency heard by the observer changes from f 1 to f 2 . If the speed of sound is v and the speed of the car is v s , the ratio f 2/f 1 is: v - v s v + v s v + v s v - v s v v + v s v - v s v A source of sound moves towards a stationary observer with a speed such that the frequency heard by the observer is twice the actual frequency. If v is the speed of sound, the speed of the source is: v/2 v/4 2v v When the intensity of a sound source increases by a factor of 10 , the sound pressure level increases by 10 dB . If the intensity increases by a factor of 400 , the sound level increases by approximately: 26 dB 40 dB 20 dB 60 dB Tuning fork A of frequency 384 Hz gives 6 beats per second with tuning fork B . When B is filed, the beat frequency decreases to 2 . The frequency of B is: 390 Hz 378 Hz 380 Hz 392 Hz An observer is moving towards a stationary source of sound with a speed equal to 1/10 of the speed of sound. The percentage change in the apparent frequency is: 10% 5% 20% 0% A point source emits sound waves isotropically. At a distance of 2 m from the source, the intensity level is 80 dB . What will be the intensity level at a distance of 20 m ? 60 dB 70 dB 40 dB 10 dB In a stationary wave, all particles of the medium between two adjacent nodes vibrate: In the same phase but with different amplitudes In the same phase and with same amplitude With different phases and same amplitude With different phases and different amplitudes A tuning fork A of frequency 256 Hz produces 4 beats per second with another tuning fork B . When fork B is loaded with a little wax, the beat frequency remains 4 beats per second. The original frequency of B was: 260 Hz 252 Hz 256 Hz 248 Hz A car moving at 20 m/s sounds a horn of frequency 1200 Hz . A stationary observer is standing on the road. What is the frequency heard by the observer as the car approaches him? (Speed of sound = 340 m/s ) 1275 Hz 1133 Hz 1200 Hz 1320 Hz In a longitudinal stationary wave, the distance between a node of displacement and the nearest node of pressure is: /4 /2 0 /8 In a stationary wave formed in a medium, the pressure variation is maximum at: Displacement nodes Displacement antinodes Points midway between nodes and antinodes All points equally When a sound wave is reflected from a free end (boundary of a rarer medium), the reflected pressure wave undergoes a phase change of: radians 0 radians /2 radians 2 radians When the distance from a point sound source is doubled, the intensity level decreases by approximately: 6 dB 3 dB 10 dB 20 dB A bat flies at a speed of 10 m/s towards a wall while emitting ultrasonic waves of frequency 40 kHz . The frequency of the wave reflected from the wall as heard by the bat is (velocity of sound = 340 m/s ): 42.4 kHz 41.2 kHz 40.0 kHz 38.8 kHz A string of length L fixed at one end and free at the other end can vibrate in standing waves. The possible wavelengths are given by: = 4L / (2n-1) = 2L / n = L / n = 4L / n The path difference between two waves y 1 = a ( t - kx) and y 2 = a ( t - kx + /3) is: /6 /3 /2 /12 Two coherent sources of intensity I and 4I interfere at a point. The maximum and minimum possible intensities are respectively: 9I and I 5I and 3I 4I and I 25I and 9I An observer is moving towards a stationary source of sound with a speed of 1/5 th of the speed of sound. The percentage increase in the apparent frequency is: 20 % 5 % 10 % 25 % A wave pulse on a string has the form y = f(x - vt) . If the pulse is reflected from a rigid boundary, the reflected pulse is: -f(-x - vt) f(x + vt) -f(x + vt) f(-x + vt) The intensity of a sound wave is I . If the amplitude is doubled and the frequency is reduced to one-fourth, the new intensity will be: I/4 I/2 I 2I In a stationary wave, the distance between the first node and the third antinode is (if the wave starts with a node at x=0 ): 1.25 0.75 0.25 1.5 Three tuning forks of frequencies f 1, f 2, f 3 are sounded together. If f 1 = 200 Hz , f 2 = 205 Hz , and f 3 = 207 Hz , what is the number of beats heard per second? 7 2 5 12 Two tuning forks P and Q produce 6 beats per second. When Q is filed, the beat frequency becomes 4 beats per second. If the frequency of P is 500 Hz , the frequency of Q is: 494 Hz 506 Hz 500 Hz 510 Hz The sound level at a point is increased by 30 dB . By what factor has the intensity of sound increased? 1000 30 300 10 3 Two tuning forks A and B produce 5 beats per second. Fork A has frequency 512 Hz . When fork B is filed, the beat frequency decreases to 2 beats per second. The original frequency of fork B was: 517 Hz 507 Hz 514 Hz 510 Hz Two waves of same frequency and intensity I 0 have a phase difference of 120 . The resultant intensity is: I 0 2I 0 3I 0 4I 0 In a stationary wave, the distance between any two consecutive nodes is 0.5 m . If the velocity of the wave is 200 m/s , the frequency of the wave is: 200 Hz 400 Hz 100 Hz 50 Hz The distance between the 1 st node and the 4 th node in a standing wave is 60 cm . The wavelength is: 40 cm 20 cm 30 cm 120 cm Ten identical sound sources, each of intensity level 20 dB , are sounded together. The resultant intensity level is: 30 dB 200 dB 40 dB 21 dB Two coherent sources of intensity I 1 and I 2 produce an interference pattern. If the ratio I 1/I 2 = 9 , then the ratio of maximum to minimum intensity is: 4:1 3:1 9:1 16:1 A tuning fork P of frequency 250 Hz produces 5 beats with another fork Q . When Q is loaded with a small piece of wax, the beat frequency remains 5 . The frequency of Q is: 255 Hz 245 Hz 250 Hz 260 Hz A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m/s . Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take velocity of sound in air as 330 m/s ): 838 Hz 800 Hz 765 Hz 850 Hz Two periodic waves of intensities I 1 and I 2 pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is: 2(I 1 + I 2) I 1 + I 2 ( I 1 + I 2 ) 2 ( I 1 - I 2 ) 2 A train moving at a speed of 220 m/s towards a stationary object emits a sound of frequency 1000 Hz . Some of the sound is reflected back from the object as an echo. The frequency of the echo heard by the driver of the train is (speed of sound = 330 m/s ): 5000 Hz 3000 Hz 4000 Hz 3500 Hz A source of sound and an observer are moving towards each other with the same speed v/10 , where v is the speed of sound. The percentage change in frequency observed is approximately: 22 % 10 % 20 % 11 % A source of sound of frequency f is moving in a circle of radius R with constant angular velocity . A stationary observer is located far away in the plane of the circle. The difference between the maximum and minimum frequencies heard by the observer is (where v is speed of sound): 2fv R v 2 - 2 R 2 2fv R v 2 fv R v + R 2f R v Two tuning forks A and B vibrating together produce 4 beats/s. Frequency of A is 250 Hz . When A is loaded with wax, 2 beats/s are heard. The frequency of B is: 246 Hz 254 Hz 252 Hz 248 Hz The distance between a node and the next adjacent antinode in a stationary wave is: /4 /2 2 If the tension and diameter of a sonometer wire of fundamental frequency n are both doubled and density is kept constant then its new fundamental frequency will be: n / 2 n 2 n n/2 For sound waves, if the number of nodes for the 5th harmonic of an open-ended pipe is n and that for the 9th harmonic of the same pipe with one of its ends closed is m , the ratio n m is 5 9 9 5 1 3 5 When a wave undergoes reflection at a rigid boundary, the phase change produced is: /2 zero 2 A string is stretched between two rigid supports. The third harmonic frequency is 300 Hz . The fundamental frequency is: 100 Hz 300 Hz 900 Hz 150 Hz