What is Sound?
Sound is a vibration that typically propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid.
Properties of Sound
  • Loudness: The sensation of a sound perceived in a ear is measured by the term loudness (depends on intensity of sound and sensitiveness of the ear). Unit of loudness is bel. A practical unit of loudness is decibel (dB) which is 1/10th of bel. Another unit of loudness is phon
  • Pitch: The characteristic of sound which distinguishes a sharp or shrill sound from a grave or dull sound. It depends upon frequency. Higher the frequency higher will be the pitch and shriller will be the sound and vice versa.
  • Frequency: The number of occurrences of a repeating event per unit of time.

Types of Waves
  1. Mechanical Waves: Acts as the propagation of a disturbance through a material medium due to the repeated periodic motion of the particles of the medium about their mean positions, the disturbance being handed over from one particle to the next. Types: Transverse and Longitudinal Waves.
  2. Electromagnetic Waves: The disturbance, which doesn't require any material medium for its propagation and can travel through vacuum. They are caused due to varying electric and magnetic fields. Types: (Radio, Micro, Infrared Rays, Visible Light, Ultraviolet, X Rays, Gamma Rays)..
  3. Matter Waves: The waves produced in electrons and particles.
Transverse Waves: A moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer(or the propagation of the wave).
Longitudinal Waves: The particle movement is parallel to the direction of the wave propagation.
Radio Waves: Emitted by radio stations by antennas used for data transmission via modulation.
Micro Waves: Emitted by microwave oven, used by Wi-fi.
Infrared Waves: Emitted by everything that is warm and hot.
Visible Light: Emitted by bulb are detected by human eye.
Ultraviolet: Emitted by sun.
X Rays: Used by doctors.
Gamma Rays: Emitted by radioactive substances. Used in treatment of many diseases.
Surface Waves: Can have mechanical or electromagnetic nature. E.g. Sea creature can create surface wave (also called as Rayleigh Waves.).
Elastic Waves: The waves produced by elastic bodies.
Sound Waves: The propagation of waves taking place in solid, liquid and gases which makes us hear the sound.

# Key Points
  • Sound waves are Longitudinal Waves
  • The speed of sound in air is approximately 331.5 m/s at 0oC and 343 m/s at 20oC (normal temperature) and 346 m/s at 25oC.
  • The speed of sound increases with the increase of temperature of the medium.
  • Due to refraction, sound is heard at longer distances in nights than in day.
  • Audible waves are lies in the range of 20 Hz to 20,000 Hz.
  • The speed of sound is highest in solid. The speed of sound depends on the density of the medium through which it is travelling. The higher the density of the medium, the faster is the propagation of sound.