0How are sound waves produced and detected?
Sound waves are a form of mechanical energy and produced by vibrating bodies. A vibrating object creates a disturbance in the surrounding air. This disturbance causes the surrounding molecules to vibrate. These molecules, in turn, vibrate the neighbouring ones. Thus these vibrations progress in the medium until they reach the ear. The ear has a very thin membrane called the eardrum or tympanum. The vibrations of the air molecules close to the ear cause the tympanum to vibrate. The vibrations of the tympanum are communicated through the nerves to the brain, causing the sensation of a sound.
Describe an experiment to show that sound cannot travel in a vacuum?
Arrange an electric bell inside a bell jar through as tight cork fitted to its mouth. Close the other end with a lid containing an outlet as shown. Connect the outlet to a vacuum pump. Precautions should be taken such that the bell jar is airtight. If the bell is rung by making the electric connections, the sound is heard. Now operate the vacuum pump so that the air inside starts getting sucked out. During this, if the bell is operated, the intensity of the sound will have decreased. Finally, when all the air inside is removed, thereby creating a vacuum, no sound can be heard at all. This proves that sound waves cannot travel through a vacuum. They require a medium for their propagation.
What is the difference between a musical note and noise?
| Musical note | Noise |
| They are pleasant to hear | They are very unpleasant to hear |
| The resulting sound waves are regular and systematic following a particular rhythm. | The sound waves are irregular without any rhythm and order. |
| Example: sound produced by musical instruments. | Example: sound produced by vehicles, industries, a stone falling on a tin roof etc. |
What are the different types of musical instruments? Give examples and explain their working.
Musical instruments are classified into three kinds:
- Stringed instruments: They contain strings of varying thickness fixed on hollow wooden boards with different tensions. When they are vibrated while changing their vibrating lengths using a method called plucking, different sounds are produced. The type of sound depends upon the tension in the string, thickness, and vibrating length—examples: Sitar, Violin, Veena etc.
- Drum instruments: They are cylindrically fitted with membranes under different tensions on the two sides. The membrane is vibrated by hands or sticks to produce different sounds—examples: Mridangum, Table etc.
- Blow type (wind) instruments: These instruments have cylindrical tubes open at both ends with holes in a row on their top surface. Air is blown through them, and by changing the length of the vibrating air column using fingers to block the different holes, different sounds are produced. Example: Flute, Clarinet etc.
What are the sound waves?
Sound waves are the disturbances created in a medium by vibrating bodies. They are longitudinal waves and a form of mechanical energy.
How are sound waves produced?
Sound waves are produced when a vibrating body causes disturbance in the surrounding air which starts progressing through the medium through compressions and rarefactions.
What changes occur in the medium while sound waves are travelling through it?
When sound waves are travelling through a medium, compressions and rarefactions are formed in it as a result of the vibratory motion of the molecules.
What is the important characteristic of longitudinal waves?
In longitudinal waves, the direction of vibration of the particles of the medium is parallel compared to the direction of motion of the wave.
What is meant by a musical note?
A musical note is a sound that is pleasant to hear. The resultant sound waves are regular, systematic and follow a particular rhythm—examples: sounds produced by musical instruments like piano and sitar.
What is meant by noise?
Noise is a sound that is very unpleasant to hear. The resultant sound waves are irregular and without any order or rhythm. Examples: sound due to vehicles and industries.
Can sound travel through liquids and solids, and what is the comparative speed?
Sound can travel through liquids and solids. The velocity of sound is greater is solids compared to liquids and higher in liquids compared to gases.
What are compressions and rarefactions?
Sound waves travelling through a medium produce compressions and rarefactions in them. Compressions are regions of high density as the space between the molecules decreases. On the other hand, rarefactions are regions of lower density due to an increase in the space between molecules.
