Tiêu đề 15.WAVES - Questions.pdf ✅

15.WAVES (1.)Intensity level of sound of intensity I is 30 dB. The ratio I I0 is (Where I0 is the threshold of hearing) (a.) 3000 (b.) 1000 (c.) 300 (d.) 30 (2.)An organ pipe, open from both end produces 5 beats per second when vibrated with a source of frequency 200 Hz. The second harmonic of the same pipes produces 10 beats per second with a source of frequency 420 Hz. The frequency of source is (a.) 195 Hz (b.) 205 Hz (c.) 190 Hz (d.) 210 Hz (3.)Stationary waves of frequency 300 Hz are formed in a medium in which the velocity of sound is 1200 metre/sec. The distance between a node and the neighbouring antinode is (a.) 1 m (b.) 2 m (c.) 3 m (d.) 4 m (4.)The phase difference between two points separated by 1m in a wire of frequency 120 Hz is 90o . The wave velocity is (a.) 180 m/s (b.) 240 m/s (c.) 480 m/s (d.) 720 m/s (5.)A tuning fork of frequency 500 Cycles/s is sounded on a resonance tube. The first and second resonance is obtained at 17 cm and 52 cm. the velocity of sound in ms −1 is (a.) 175 (b.) 350 (c.) 525 (d.) 700 (6.)The equation of a transverse wave is given by y = 10 sin π(0.01x − 2t) Where x and y are in cm and t is in second. Its frequency is (a.) 10 sec−1 (b.) 2 sec−1 (c.) 1 sec−1 (d.) 0.01 sec−1 (7.)A pipe open at both the ends produce a note of fundamental frequency v1 When the pipe is kept with 3 4 th of its length in water, it produces a note of fundamental frequency v2. The ration of v1 v2 is (a.) 4 3 (b.) 3 4 (c.) 2 (d.) 1 2 (8.)Which of the following is different from others (a.) Velocity (b.) Wavelength (c.) Frequency (d.) Amplitude (9.)An organ pipe P closed at one end vibrates in its first harmonic. Another organ pipe Q open at both ends vibrates in its third harmonic. When both are in resonance with a tuning fork, the ratio of the length of P to that of Q is (a.) 1/2 (b.) 1/4 (c.) 1/6 (d.) 1/8 (10.)Two sources of sound placed to each other, are emitting progressive waves given by y1 = 4 sin 600πt and y2 = 5 sin 608πt. An observer located near these two sources of sound will hear (a.) 4 beats per second with intensity ratio 25 : 16 between waxing and waning (b.) 8 beats per second with intensity ratio 25 : 16 between waxing and waning (c.) 8 beats per second with intensity ratio 81 : 1 between waxing and waning (d.) 4 beats per second with intensity ratio 81 : 1 between waxing and waning (11.)A string vibrates with a frequency of 200 Hz. When its length is doubled and tension is altered, it begins to vibrate with a frequency of 300 Hz. The ratio of the new tension to the original tension is (a.) 9:1 (b.) 1:9 (c.) 3:1 (d.) 1:3 (12.)The fundamental frequency of a string stretched with a weight of 4 kg is 256 Hz. The weight required to produce its octave is (a.) 16 kg-wt (b.) 12 kg-wt (c.) 24 kg-wt (d.) 4 kg-wt
(13.)A sine wave has an amplitude A and a wavelength λ.Let v be the wave velocity, and V be maximum velocity of a particle in the medium (a.) V cannot be equal to v (b.) V − v,if A = λ/2π (c.) V − v,if A = 2πλ (d.) V − v,if λ = A/π (14.)The frequency of fundamental note in an organ pipe is 240 Hz. On blowing air, frequencies 720 Hz and 1200 Hz are heard. This indicates that organ pipe is (a.) A pipe closed at one end (b.) A pipe open at both ends (c.) Closed at both ends (d.) Having holes like flute (15.)The wavelength of a wave is 990 cm and that of other is 100 cm. speed of sound is 396 m/s. The number of beats heard is (a.) 4 (b.) 5 (c.) 1 (d.) 8 (16.)Two tuning fork of frequency n1and n2 produces n beats per second. If n2 and n are known, n1may be given by (a.) n2 n + n2 (b.) n2n (c.) n2 ± n (d.) n2 n − n2 (17.)If the amplitude of sound is doubled and the frequency reduced to one-fourth, the intensity of sound at the same point will be (a.) Increased by a factor of 2 (b.) Decreased by a factor of 2 (c.) Decreased by a factor of 4 (d.) Unchanged (18.)Sound waves of v=600Hz fall normally on a perfectly reflecting wall. The shortest distance from the wall at which all particles will have maximum amplitude of vibration will be (speed of sound=300ms −1 ) (a.) 7 8 m (b.) 3 8 m (c.) 1 8 m (d.) 1 4 m (19.)A source of frequency n given 5 beats s −1 , when sounded with a source of frequency 200 s −1 . The second harmonic (2n) gives 10 beats s −1 , when sounded with a source of frequency 420 s −1 . n is equal to (a.) 200 s −1 (b.) 205 s −1 (c.) 195 s −1 (d.) 210 s −1 (20.)A car is moving with a speed of 72 kmh −1 towards a hill. Car blows horn at a distance of 1800 m from the hill. If echo is heard after 10s, the speed of sound (in ms −1 )is (a.) 300 (b.) 320 (c.) 340 (d.) 360 (21.)The equation of wave is represented by Y = 10−4 sin [100t − x 10] m, then the velocity of wave will be (a.) 100ms −1 (b.) 4ms −1 (c.) 1000ms −1 (d.) zero (22.)A bomb explodes on the moon. How long will it take for the sound to reach the earth? (a.) 1000 s (b.) 1 day (c.) 10 s (d.) None of these (23.)A 20 cm long string, having a mass of 1.0 g, is fixed at both the ends. The tension in the string is 0.5 N. the string is set into vibration using an external vibrator of frequency 100 Hz. Find the separation (in cm) between the successive nodes on the string (a.) 5 (b.) 6 (c.) 2 (d.) 3/2 (24.)In a medium sound travels 2 km in 3 sec and in air, it travels 3 km in 10 sec. The ratio of the wavelengths of sound in the two media is (a.) 1 ∶ 8 (b.) 1 ∶ 18 (c.) 8 ∶ 1 (d.) 20 ∶ 9 (25.)The following equations represents progressive transverse waves Z1 = A cos(ωt − kX), Z2 = A cos (ωt + kX), Z3 = A cos (ωt − kY), Z4 = A cos (2ωt − 2kY). A stationary wave will be formed by superposing (a.) Z1and Z2 (b.) Z1and Z4 (c.) Z2and Z3 (d.) Z3and Z4 (26.)The equation of stationary wave along a stretched string is given by y = 5 sin πx 3 cos 40πt where x and y are in centimetre and t in second. The separation between two adjacent nodes is :
(a.) 6 cm (b.) 4 cm (c.) 3 cm (d.) 1.5 cm (27.)Two sources produce sound waves of equal amplitudes and travelling along the same direction producing 18 beats in 3 seconds. If one source has a frequency of 341 Hz, the frequency of the other source may be (a.) 329 or 353 Hz (b.) 335 or 347 Hz (c.) 338 or 344 Hz (d.) 332 or 350 Hz (28.)Two sound waves having a phase difference of 60o have path difference of (a.) 2λ (b.) λ/2 (c.) λ/6 (d.) λ/3 (29.)A source emits a sound of frequency of 400 Hz, but the listener hearts its 390 Hz. Then (a.) The listener is moving towards the source (b.) The source is moving towards the listener (c.) The listener is moving away from the source (d.) The listener has a defective ear (30.)What is minimum length of a tube, open at both ends, that resonates with tuning fork of frequency 350 Hz ? [velocity of sound in air = 350 m/s] (a.) 50 cm (b.) 100 cm (c.) 75 cm (d.) 25 cm (31.)A tuning fork makes 256 vibrations per second in air. When the velocity of sound is 330 m/s, then wavelength of the tone emitted is (a.) 0.56 m (b.) 0.89 m (c.) 1.11 m (d.) 1.29 m (32.)The apparent frequency of the whistle of an engine changes in the ratio 9:8 as the engine passes a stationary observer. If the velocity of the sound is 340ms −1 , then the velocity of the engine is (a.) 40 ms −1 (b.) 20 ms −1 (c.) 340 ms −1 (d.) 180 ms −1 (33.)A stretched string of length lfixed at both ends can sustain stationary waves of wavelength λ given by (a.) λ = 2ln (b.) λ = 2l/n (c.) λ = l 2 /2n (d.) λ = n 2 /2l (34.)The phenomenon of sound propagation in air is (a.) Isothermal process (b.) Isobaric process (c.) Adiabatic process (d.) None of these (35.)A wave frequency us y=0.1 sin [100 πt − kx] and wave velocity is 100−1 , its wave number is equal to (a.) 1m−1 (b.) 2m−1 (c.) πm−1 (d.) 2π m−1 (36.)In a plane progressive wave given by y = 25 cos(2πt − πx), the amplitude and frequency are respectively (a.) 25,100 (b.) 25,1 (c.) 25,2 (d.) 50π, 2 (37.)Find beat frequency? Motion of two particles is given by y1 = 0.25 sin(310t) y2 = 0.25 sin(316t) (a.) 3 (b.) 3 π (c.) 6 π (d.) 6 (38.)What should be the velocity of a sound source moving towards a stationary observer so that apparent frequency is double the actual frequency (Velocity of sound is v) (a.) v (b.) 2v (c.) v 2 (d.) v 4 (39.)Which one of the following statements is true (a.) Both light and sound waves in air are longitudinal (b.) Both light and sound waves can travel in vacuum (c.) Both light and sound waves in air are transverse (d.) The sound waves in air are longitudinal while the light waves are transverse (40.)In open organ pipe, if fundamental frequency is n then the other frequencies are (a.) n, 2n, 3n, 4n (b.) n, 3n, 5n (c.) n, 2n, 4n, 8n (d.) None of these (41.)Source of sound and the observer are mutually at rest. If speed of sound is changed, then the
frequency of sound heard by the observer will appear to be (a.) Increased (b.) Decreased (c.) Unchanged (d.) Decreasing exponentially (42.)Fundamental frequency of sonometer wire is n. If the length, tension and diameter of wire are tripled, the new fundamental frequency is (a.) n √3 (b.) n 3 (c.) n√3 (d.) n 3√3 (43.)Two travelling waves y1 = A sin[k(x − ct)] and y2 = A sin[k(x + ct)] are superimposed on string. The distance between adjacent nodes is (a.) ct/π (b.) ct/2π (c.) π/2k (d.) π/k (44.)The two interfering waves have intensities in the ratio 9 : 4. The ratio of intensities of maxima and minima in the interference pattern will be (a.) 1 : 25 (b.) 25 : 1 (c.) 9 : 4 (d.) 4 : 9 (45.)Ultrasonic waves are produced by (a.) Piezoelectric effect (b.) Pettiro’s effect (c.) Doppler’s effect (d.) Coulomb’s law (46.)The length of two open organ pipes are l and (l + ∆l) respectively. Neglecting end correction, the frequency of beats between them will be approximately (a.) v 2l (b.) v 4l (c.) v∆l 2l 2 (d.) v∆l l (47.)If the velocity of sound in air is 336 m/s. The maximum length of a closed pipe that would produce a just audible sound will be (a.) 3.2 cm (b.) 4.2 m (c.) 4.2 cm (d.) 3.2 m (48.)A source of sound gives 5 beats s −1 when sounded with another source of frequency 100 Hz. The second harmonic of the source together with a source of frequency 205 Hz gives 5 beats s −1 . What is the frequency of the source? (a.) 105 Hz (b.) 205 Hz (c.) 95 Hz (d.) 100 Hz (49.)A source and an observer are moving towards each other with a speed equal to v 2 where v is the speed of sound. The source is emitting sound of frequency n. The frequency heard by the observer will be (a.) Zero (b.) n (c.) n 3 (d.) 3n (50.)A stretched string of length l fixes at both ends can sustain stationary waves of wavelength λ, given by (a.) λ =2ln (b.) λ = ι 2 n (c.) λ = ι 2 2n (d.) λ = n 2 2ι (51.)The phase difference between two points separated by 0.8 m in a wave of frequency is 120 Hz is π/2. The velocity of wave is (a.) 720 m/s (b.) 384 m/s (c.) 250 m/s (d.) 1 m/s (52.)If wavelength of a wave is λ = 6000Å. Then wave number will be (a.) 166 × 103m−1 (b.) 16.6 × 10−1m−1 (c.) 1.66 × 106m−1 (d.) 1.66 × 107m−1 (53.)A point source emits sound equally in all direction in a non-absorbing medium. Two points P and Q are at distance of 2 and 3 m respectively from the source. The ratio of the intensities of the wave at P and Q is. (a.) 9:4 (b.) 2:3 (c.) 3:2 (d.) 4:9 (54.)Sound waves travel at 350 m/s through a warm air and at 3500 m/s through brass. The wavelength of a 700 Hz acoustic wave as it enters brass from warm air (a.) Decreases by a factor 20 (b.) Decreases by a factor 10 (c.) Increases by a factor 20 (d.) Increases by a factor 10