Sound is a form of energy, just like electricity, heat or light. When you strike a bell, it makes a loud ringing noise. Now instead of just listening to the bell, put your finger on the bell after you have struck it. Can you feel it shaking? This movement or shaking, i.e. the to and fro motion of the body is termed as Vibration. Sound is a vibration that moves as an audible form of energy through a medium. The sound moves through a medium by alternatively contracting and expanding parts of the medium it is travelling through. The movement of molecules of a medium is essential for the propagation of sound waves. Hence sound waves cannot travel through the emptiness of vacuum.
Sound cannot travel through vacuum. This is very much in contrast with the property of light. Another difference which is above the scope of the syllabus is the fact that sound waves are generally longitudinal waves and light waves are transverse waves . But they’re not very different either. Let’s take a look at the characteristics of sound when propagating through air.
Reflection of Sound Waves:
This property of sound is responsible for the phenomenon of Echo. Also the rolling of thunder is largely due to the repeated reflections from the clouds and land surfaces. The reflection of sound follows the same principle as light waves. The angle of incidence is equal to the angle of reflection. For an appreciable reflection the reflecting surface should have a large surface area, like a cloud. This principle of reflection is used in a technology known as SONAR (Sound Navigation and Ranging) where the sound waves are used, usually underwater, to navigate and communicate. The sound waves that reflect from objects are used to detect objects on or under the surface of water.
Refraction of Sound Waves:
Refraction in light occurs when the density of the medium in which light is travelling changes. Similarly, Refraction in Sound occurs when the density of the atmosphere it is travelling through changes. The density of a gas decreases with the rise in temperature, inversely proportional. In fact it is so similar to light waves that it even undergoes Total Internal Reflection.
Diffraction of Sound Waves:
Think about this for a minute. If you shut the door and shout for your friend outside your room, he can still hear you. Sound waves have the ability to bend around obstacles. If there is a small hole in the door, the small opening itself would act like a localized source of sound. Diffraction of sound waves is an important part of our experience of the world around us. The lightning strikes close to you sound like a sharp crack and yet the distant strikes sound of deep rumbling thunder. This is because the deeper tones of sound waves can bend across obstacles better than the sharp sounds so you hear only the deep rumbling. Light waves too undergo diffraction but of a significantly lesser magnitude.
We started off saying sound and light waves are not alike at all. But by the end, sound seemed more like light waves. The understanding of science is very similar to this. Learn the right way, download Byju’s The Learning App to watch interactive videos. Watch the video below to visualize these waves.