[GS] [Science] Wave, Mechanical Wave, Sound Wave For All Competitive Exams

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[GS] [Science]

Wave, Mechanical Wave, Sound Wave For All Competitive Exams

• Wave : A wave is a disturbance which propagates energy from one place to the other without the transport of matter.

• Waves are of two types

• (1) Mechanical wave

• (2) Non-Mechanical wave

• Mechanical Wave : The waves which require material medium (solid, liquid or gas) for their propagation are called mechanical waves or elastic waves. Mechanical waves are of two types:

• (1) Longitudinal wave : If the particles of the medium vibrate in the direction of propagation of wave, the wave is called longitudinal wave. Waves on springs or sound waves in air are examples of longitudinal waves.

• (2)Transverse Wave : If the particles of the medium vibrate perpendicular to the direction of propagation of wave, the wave is called transverse wave. Waves on strings under tension, waves on the surface of water are examples of transverse waves.

• (2) Non-Mechanical waves or Electromagnetic waves : The waves which do not require medium for their propagation i.e which can propagate even through the vacuum are called non mechanical wave. Light, heat are the examples of non-mechanical wave. In fact all the electromagnetic waves are non-mechanical.

• All the electromagnetic wave consists of photon.

• The wavelength range of electromagnetic wave is 10^-14 m to 10⁴

• Properties of electromagnetic waves :

• (1)They are neutral.

• (2)They propagate as transverse wave.

• (3)They propagate with the velocity of light.

• (4)They contains energy and momentum.

• (5)Their concept was introduced by Maxwell.

• Following waves are not electromagnetic: Cathode rays, Canal rays, α rays, β rays, sound wave and ultrasonic wave.

• Electromagnetic waves of wavelength range 10^-3 m to 10^-2 m are called microwaves.

• Sound wave : Sound waves are longitudinal mechanical waves. They are of three types:

• (1) Audible waves : The waves which lie in the frequency range 20 Hz to 20000 Hz are called audible waves. These waves are sensitive to human ear.

• (2) Infrasonic waves : The waves having frequencies less than 20 Hz are called infrasonic. Examples: Earthquakes, volcanic eruptions and ocean waves.

• (3) Ultrasonic waves : The waves having frequencies greater than 20000 Hz are called ultrasonic waves. Human ear cannot detect these waves but certain creatures like dog, cat etc can detect these waves. Bat not only detect but also produce ultrasonic.

• Applications of ultrasonic waves :

• (1) For sending signals.

• (2) For measuring the depth of sea.

• (3) For cleaning machinery parts of clocks.

• Speed of sound : Speed of sound is different in different mediums. In a medium, the speed of sound basically depends upon elasticity and density of medium.

• Speed of sound is maximum in solids and minimum in gases.

• When sound enters from one medium to another medium, its speed and wavelength changes but frequency remains unchanged.

• In a medium, the speed of sound is independent of frequency.

• Effect of pressure on speed of sound:

       The speed of sound is independent of pressure.

• Speed of sound is 260 m/s in Carbon dioxides.

• Speed of sound is 332 m/s in air at 0⁰

• Speed of sound is 1482 m/s in water at 20⁰

• Speed of sound is 5130 m/s in Iron.

• Speed of sound is 5640 m/s in glass.

• Speed of sound is 6420 m/s in Aluminium.

• Effect of temperature on speed of sound : The speed of sound increases with the increase of temperature of the medium. The speed of sound in air increases by 0.61 m/s when the temperature is increased by 1⁰

• Effect of humidity on speed of sound : The speed of sound is more in humid air than in dry air because the density of humid air is less than the density of dry air.

• Characteristics of sound waves : Sound waves have three characteristics:

• (1) Intensity : Due to intensity, a sound appears loud or faint to the ear. Unit of loudness is bel. A practical unit of loudness is decibel which is equal to 1/10^th of bel. Another unit of loudness is phon.

• (2) Pitch : Pitch is that characteristic of sound which distinguishes a sharp sound from a grave sound. Pitch depends upon frequency. Higher the frequency, higher will be the pitch and shriller will be the sound. Lower the frequency, lower will be the pitch and grave will be the sound.

• (3) Quality : Quality is that characteristic of sound which enables us to distinguish between sounds produced by two sources having the same intensity and pitch.