I want all the question answers of 9th class physics 5th lesson if you answer me I will make you as brainlist
Answers
1. How does the sound produced by a vibrating object in a medium reach your ear?
Ans. As we speak, the particles of air near our mouth are pushed forward so they get compressed. Then they compress the other particles of air. As the compression proceeds the particles of air near our mouth expand again and thus rarefaction occurs. This process is repeated further and as a result sound wave propagates in the form of compressions and rarefactions to the listener’s ear.
2. What are wavelength, frequency, time period and amplitude of a sound wave?
Ans. wavelength: For a sound wave, the combined length of a compression and an adjacent rarefaction is called its wavelength even the distance between centres of two consecutive compressions or two consecutive rarefactions is also equal to its wavelength.
frequency: The number of vibrations or oscillations per second is called frequency i.e. it is the number of complete waves or cycles produced in one second.
Time period: The time taken to complete one vibration/oscillation/complete wave is called time period. It is measured in seconds.
Amplitude: It is the maximum displacement of the particles of the medium from their mean/original position at rest.
3. Cite an experiment to show that sound needs a material medium for its propagation.
Ans. Take an electric bell and an airtight glass bell jar. The electric bell is suspended inside the airtight bell jar. The bell jar is connected to a vacuum pump If you press the switch you will be able to hear the bell. Now start the vacuum pump. When the air in the jar is pumped out gradually, the sound becomes fainter, although the same current is passing through the bell.
After some time when less air is left inside the bell jar you will hear a very feeble sound. Now if we evacuate the bell jar no sound is heard.
Result: The above mentioned activity shows that sound needs a medium to propagate.
4. What happens when sound travels in air?
Ans. When sound wave travels through air then the pressure and density of air changes. As the disturbance propagates through a medium, then alternate regions of pressure variations are created.
The region where particle come closer to each other (high density) and pressure of air is high is called as compression. The region where particles far apart from each other (low density) and pressure of air is less is called as rarefaction compression and rarefactions always occur together.
5. Establish the relation for a wave that velocity = frequencywavelength.
Ans. Since, velocity =
For a wave, for one vibration, the distance b/w two consecutive crest or trough is called its wavelength.
Time required to complete one vibration is called its Time Period (T).
(Frequency) is defined as the no. of vibrations particle covers in 1 second.(3mark)
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