Concise Selina Solutions for Class 8 Physics Chapter 7 Sound

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. Sound explains how vibration or the back and forth movement of an object produce sound. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. A material medium is required for the propagation of sound. As there is no material in the vacuum, sound cannot propagate through it. Sound can be of different types - soft, loud, pleasant, unpleasant, musical, audible (can be heard), inaudible (cannot be heard), etc. Some sounds may fall into more than one category. For instance, the sound produced when an aeroplane takes off is both loud and unpleasant. The loudness of a sound depends on the amplitude of the wave. The bigger the amplitude, the louder the sound. Some sounds can be so loud that they can damage the ear. This is because the huge amplitude of the sound wave makes the ear drum move back and forth too violently.