Ans. Common features of longitudinal and transverse waves: 1) In both waves, particles of the medium vibrate about their mean position. 2) Transport energy and momentum but not matter. 3) When propagate in a medium they obey, v = f λ
Q.2 The five possible waveforms obtained when the output from a microphone is fed into the Y-input of cathode ray oscilloscope, with the time base on, are shown in the fig.These waveforms are obtained under the same adjustment of the cathode ray oscilloscope controls. Indicate the waveform
a) which trace represents the loudest note?
b) which trace represents the highest frequency?
Ans. a) trace B represents the loudest note. b) trace B represents the highest frequency.
Q.3 Is it possible for two identical waves travelling in the same direction along a string to
give rise to a stationary wave?
Ans. No. It is not possible. For stationary waves two identical waves should travel in opposite direction along a string.
Q.4 A wave is produced along a stretched string but some of its particles permanently show zero displacement. What type of wave is it?
Ans. Stationary wave. Here nodal points show permanently zero displacement.
Q.5 Explain the terms crest, trough, node and antinode.
Ans. Crest: “The portion of a wave above the mean level”. It is a region of upward displacement in a transverse wave. Trough: “The lower portion of a wave below the mean level”. It is region of downward displacement in a transverse wave. Node: “The point of zero displacement”. It is a point of no disturbance in a stationary wave. Antinode: “The point of maximum displacement on a stationary wave”. It is a point which oscillate with maximum amplitude in a stationary wave.
Q.6 Why does sound travel faster in solids than in gases?
Ans. In the relation v = √ E / ρ E is greater for solids than in gases. The effect of density, ρ is very less as compared to E. so sound travel faster in solids then in gases.
Q.7 How are beats useful in tuning musical instruments?
Ans. A new instrument is tuned. The new, and standard musical instruments are sounded together, beats are produced. The frequency of the new instrument is made to change until the resonance occurs.
Q.8 When two notes of frequencies f1 and f2 are sounded together, beats are formed.
If f1 > f2 , what will be the frequency of beats?
i) f1 + f2 ii) ½ (f1 + f2 ) iii) f1 - f2 iv) ½ (f1 - f2 )
Ans. Correct answer is (iii) ( f1 - f2 ) Number of beats per second is equal to the difference between the frequencies of the tuning forks.
Q.9 As a result of distant explosion, an observer senses a ground tremor and then hears the explosion. Explain the time difference.Ans. Sound waves travel faster in solids than in air. The sound waves produced by the explosion travel two paths. One through earth reaches faster than traveling through atmosphere. This accounts for the time difference.
Q.10 Explain why sound travels faster in warm air than in cold air.
Ans. v ∝ √T ; v = √ γ P / ρ The speed of sound varies directly as the square root of absolute temperature. That’s why sound travels faster in warm air than in cold air. As the temperature of air increases, the pressure increases and density decreases. So speed of sound increases.
Q.11 How should a sound source move with respect to an observer so that the frequency of its sound does not change?
Ans. Relative speed should be zero. From Doppler effect, there is apparent change in the frequency due to relative motion of source and observer. When both source of sound and observer are in motion, relative speed being zero, the apparent frequency will not change.
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