Sound Waves

Sound is a type of energy that we can hear. It is produced when something vibrates, and these vibrations travel through the air to reach our ears. Our ears pick up sound vibrations and send signals to our brain. The brain then interprets these signals as different kinds of sounds.

• Loud sounds that can be heard easily, even from a distance. Examples include thunder, a car horn, or a drum.
• Soft sounds are gentle and quiet sounds that may be hard to hear unless we pay attention. Examples include the ticking of a clock or the rustling of leaves.

A wave is a disturbance produced in a medium as the particles vibrate. The particles produce motion in each other without moving forward or backward, leading to sound propagation. Hence, the sound is often called a wave.

• When an object vibrates in the air or produces a sound, some regions of high pressure are created in front of it. These are called the Regions of Compression.
• These compression regions move forward in the medium as particles exert pressure on adjacent particles. With alternate regions of compression, there are also regions of low pressure in its front. These are called regions of rarefaction.
• As the object moves forwards and backwards consecutively, producing sound, a series of compressions and rarefactions will be created. This will also allow sound to move through air or any other medium.
• If the medium is dense, the pressure exerted on the particles will be greater to propagate the sound, and vice versa. Therefore, we can also say that sound propagation is all about a change in the pressure of the medium.

A wave produced when objects of the medium oscillate is called a mechanical wave. Sound cannot travel through the vacuum, as it always needs a medium to propagate. The vacuum contains no air; hence, no particles can propagate sound.

1. Longitudinal waves: Any wave that vibrates in the direction of the motion is called a longitudinal wave. Sound waves are longitudinal because the particles of the medium vibrate in a direction parallel to the direction of the propagation of the sound waves. The particles in the medium oscillate to and fro in the case of longitudinal waves.
2. Transverse Waves: A transverse wave is produced when the particles of the medium oscillate in a direction perpendicular to the direction of the propagation of the wave. The particles in a transverse wave oscillate in an up-and-down motion. For example, light waves are transverse in nature.

Our ears are sensitive only to a limited range of frequencies from 20 Hz to 20,000 Hz, which is called the audible range of frequency.

The sound of frequency above 20,000 Hz is called ultrasonic.

The sound of frequency below 20 Hz is called infrasonic.

When a sound wave travels in a medium, the maximum displacement of the particle of the medium on either side of its mean position, is called the amplitude (a) of the wave.

The time taken by the particle of the medium to complete its one vibration, is called the time period (T) of the wave.

The number of vibrations made by the particle of the medium in one second, is called the frequency (j) of the wave.

The distance travelled by a wave in one time period of vibration of the particle of the medium, is called the wavelength (λ).

The distance travelled by the wave in one second is called the wave velocity (V).

If the vibrations of medium particles are along the direction of propagation of the wave, thus forming compressions and rarefactions in the medium, the wave is called a longitudinal wave.

If the medium particles vibrate normal to the direction of propagation of the wave, forming crests and troughs, the wave is called a transverse wave.