Gradually due to friction, the strip losses its energy to the medium and the disturbance dies out. In this manner, as the strip moves to the right and left repeatedly, the compressions and rarefactions regions are produced one after the other which carry the disturbance with it with a definite speed depending on the nature of the medium. When the strip returns from c to it's normal position a, it pushes the rarefaction R forward and the air layers near the strip again pass through their mean positions due to the elasticity of the medium. This region of low pressure is called the rarefaction R. The air layers on the right side of the strip expand in this region thus forming the rarefied air layers. When the strip moves to the left from a to c, it pushes back the layers of air near it towards it's left and thus produces a space of very low pressure on it's right side. The particles of the medium get displaced, but they do not move along with the compression.Īs the metal strip starts returning from b to a as shown in figure, after pushing the particles in front, the particles of air near the strip starts returning back to their mean positions due to the elasticity of the medium. Thus, the disturbance moves forward in form of compression. The particles of these layers while moving forward, push and compress the layers next to them, which then compress the next layers and so on. So the particles of air in these layers gets closer to each other i.e., air of these layers gets compressed. When the strip advances to the right from a to b, it pushes the particles of air in layers in front of it. As it vibrates (i.e., moves alternatively to the right and left) sound is heard. Push it's upper end to one side and then release it. This can be understood by the following example.
The disturbance then travels in the medium in the form of waves. When a source of sound vibrates, it creates a periodic disturbance in the medium near it.
Question 8Įxplain with an example, the propagation of sound in a medium. (c) The medium should be frictionless so that there is no loss of energy in propagation of sound through it. (b) The medium must have inertia so that it's particles may store mechanical energy. (a) The medium must be elastic so that it's particles may come back to their initial position after displacement on either side, i.e., the particles are capable of vibrating about their mean position. The characteristics of the medium required for propagation of sound in a medium are. State three characteristics of the medium required for propagation of sound? No, we cannot hear each other on the moon's surface because there is no medium for the propagation of sound on moon.
Can you hear each other on the moon’s surface? This clearly demonstrates that sound requires a material medium for it's transmission and it cannot travel through vacuum.
But when air has been removed from the jar, sound produced due to vibrations of the gong could not travel to the wall of the jar, so wall could not vibrate and no sound is heard. This causes the wall of jar to vibrate due to which the air outside the jar is also set in vibration. When the hammer of the bell hits the gong, sound is produced due to vibration of the gong which travels through the air to the wall of the jar. The hammer of electric bulb is still seen striking the gong repeatedly which means that the gong is still vibrating to produce sound (as hammer strikes the gong), but it is not heard. It is noticed that the loudness of sound goes on decreasing as the air is taken out from the bell jar and finally no sound is heard when the entire air from the jar has been drawn out. Now keeping the key pressed, air is gradually withdrawn from the jar by starting the vacuum pump. As the circuit of electric bulb is completed by pressing the key, the hammer of the electric bell is seen to strike the gong repeatedly and sound of the bell is heard.
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