Sound Wave

What is Sound?

Sound is a form of mechanical wave that propagates through a medium (such as air, water, or solids) due to the vibration of particles. Unlike light, sound cannot travel through a vacuum and requires a medium for transmission.

Characteristics of Sound Waves

• Frequency (f): The number of oscillations per second, measured in Hertz (Hz). It determines the pitch of the sound.
• Amplitude (A): The maximum displacement of particles from their equilibrium position. Amplitude determines the loudness of the sound.
• Wavelength (λ): The distance between two consecutive points in phase, such as crest to crest or trough to trough.
• Speed (v): The speed at which sound propagates through a medium. The speed of sound depends on the medium and its properties (e.g., density and temperature).

Speed of Sound

The speed of sound in a medium depends on its properties such as temperature and density. The general equation for the speed of sound is:

v = √(B/ρ)

Where:

• v is the speed of sound.
• B is the bulk modulus (elasticity of the medium).
• ρ is the density of the medium.

At standard conditions (20°C), the speed of sound in air is approximately 343 m/s. The speed increases in denser media such as water and steel.

Types of Sound Waves

• Longitudinal Waves: Sound waves are longitudinal, meaning the particles of the medium oscillate parallel to the direction of wave propagation. This creates compressions and rarefactions.
• Transverse Waves: In certain circumstances, such as in a stretched string, sound can also exhibit transverse motion, though this is not typical for sound propagation in air.

Reflection, Refraction, and Diffraction of Sound

Sound waves, like other waves, exhibit the behaviors of reflection, refraction, and diffraction:

• Reflection: When sound waves strike a reflective surface, they bounce back. This is the principle behind echoes.
• Refraction: When sound passes from one medium to another, its speed and direction change, leading to refraction.
• Diffraction: Sound waves can bend around obstacles or spread out after passing through small openings, creating the phenomenon of diffraction.

Loudness and Pitch

• Loudness: The perceived strength of a sound. It is directly related to the amplitude of the sound wave and is measured in decibels (dB).
• Pitch: The perceived frequency of a sound. Higher frequencies produce a higher pitch, and lower frequencies produce a lower pitch.

The human ear can hear sound waves with frequencies between approximately 20 Hz and 20,000 Hz. Below this range, sound is referred to as infrasonic, and above this range, it is ultrasonic.

Applications of Sound Waves

• Used in medical diagnostics, such as ultrasound imaging, to observe internal body structures.
• Sound waves are fundamental to communication technologies such as telephones and radios.
• Used in sonar systems for navigation and detection under water.
• In music, sound waves are essential for producing musical notes and tones.

Previous Year Questions

• RRB JE 2016: What is the speed of sound in air at 20°C?
• The speed of sound in air at 20°C is approximately 343 m/s.
• SSC JE 2017: The frequency of a sound wave is 400 Hz. What is its wavelength in air at 20°C?
• The wavelength is given by λ = v/f = 343/400 = 0.8575 meters.
• HSSC JE 2018: Which of the following statements is true for the speed of sound?
• The speed of sound increases with an increase in temperature.

Conclusion

Sound waves are integral to many aspects of our daily lives, from communication to entertainment and even medical diagnostics. Understanding the properties and behaviors of sound waves helps in their practical applications in various fields such as engineering, medicine, and entertainment.