Concise Selina Solutions for Class 7 Physics Chapter 6 Sound


In physics, the sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, the sound is the reception of such waves and their perception by the brain. Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) Vibrations in the air are called travelling longitudinal waves, which we can hear. Sound waves consist of areas of high and low pressure called compressions and rarefactions, respectively.

There are many different types of sound including, audible, inaudible, unpleasant, pleasant, soft, loud, noise and music.

Sound originates at a point and travels in all directions. Throw a stone into a still body of water and observe how the concentric circles of waves expand. The same is true with sound. "The stronger the vibrations, the louder the sound". Sounds are fainter the farther you get from the sound source. Sounds can be loud, quiet and of different notes or pitches. SONAR - SONAR stands for Sound Navigation And Ranging. A sonar technique is used for determining the depth and also locating underwater objects such as reefs, submarines etc. Bats and dolphins use their sonar to navigate. Noise Pollution - The disturbance produced in the environment by undesirable, loud and harsh sounds from various sources is called noise pollution.