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प्रश्न
Why are the waves mentioned by you not audible to us?
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उत्तर
The range of audible sound waves is 20 Hz to 20,000 Hz, whereas ultrasonic waves have a frequency of more than 20,000 Hz. Hence, ultrasonic waves are not audible to humans.
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संबंधित प्रश्न
Fig. shows three ways in which a string of length l in an instrument can vibrate.
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| (i) | (ii) | (iii) |
- Which of the diagram shows the principle note?
- Which vibration has the frequency four times that of the first?
- Which vibration is of the longest wavelength?
- What is the ratio of the frequency of the vibration in (i) and (ii)?
Define sound ranging.
A thin metal plate is placed against the teeth of cog wheel. Cog wheel is rotated at a speed of 120 rotations per minute and has 160 teeth. Calculate:
- frequency of node produced.
- speed of sound, if wavelength is 1.05 m.
- what will be the effect when the speed of cog wheel is doubled?
The distance between three consecutive crests of wave is 60 cm. If the waves are produced at the rate of 180/ min, calculate:
- wavelength
- time period
- wave velocity.
What do you mean by the frequency of sound?
Match the following.
| Ultrasonics | Frequency below 20Hz |
| Speed of sound in air | Needs material medium |
| Infrasonics | 330ms-1 |
| Sound propagation | Frequency more than 20000 Hz |
Sound travels in air:
Lightning can be seen the moment it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s).
Write any two uses of ultrasonic sound.
