wave

Disturbance which propagates energy from one place to another without transport of matter.

Waves are of two types:

Mechanical wave and Non  Mechanical wave.

Mechanical wave: The waves which require material medium(solid, liquid,gas) for their propagation.

Types of Mechanical wave:

• Longitudinal: particles of medium vibrate in the direction of propagation of wave. ex: sound wave and waves on spring.
• Transverse: Particle of the medium vibrates perpendicular to the direction of propagation. ex: waves on surface of water or waves on string under surface tension.

** Waves produced by moving motor boat on surface of water is both transverse as well as longitudinal.

Non-mechanical waves or electromagnetic waves: 

The waves which do not require medium for their propagation. ex: all electromagnetic waves such as light and heat.

All electromagnetic wave consist of photon. wavelength range 10^-14 to 10^4 m

Property of electromagnetic waves:

• They are neutral
• propagate as transverse wave
• Propagate with velocity of light
• Contains energy and momentum.
• Concept was introduced by maxwell

Following waves are not electromagnetic.

alpha and beta ray, sound wave, ultrasonic wave, cathode, canal ray.

** In electronic wave, electric field vector and magnetic field vector vibrate perpendicular to each other and also perpendicular to the direction of propagation of wave.

Relation between wavelength, frequency and velocity of wave: v = nλ .

Sound Wave:

Longitudinal mechanical wave.

sound wave divided into following category:

• Audible or sound waves: frequency range 20hz to 20000 hz.
• Infrasonic waves: Frequency less than 20hz, These waves are produced by source of bigger size such as earth quakes, volcanic eruptions, ocean waves and by elephant and whales.
• Ultrasonic waves: frequencies greater than 20000 hz, human hear cannot detect these waves, but certain creatures like dog, cat, bat mosquito can detect, Bats can detect and also produced.

Ultra sonic waves can be produced by Galton's whistle or hartman's generator or by high frequency vibration of quartz crystal under an alternative electric field (piezo-electric effect).

Application of Ultrasonic waves:

• Sending signal, measuring the depth of sea
• for cleaning cloths, aeroplane and machinery parts of clocks
• In ultrasonography, IN sterilizing of a liquid, For removing lamp-shoot from the chimeny of factories.

Speed of sound:

• It basically depends upon elasticity and density of medium. 
• maximum in solid and minimum in gases.
• In a medium, the speed of sound is independent of frequency.

Wavelength of sound in air is effected by air temperature.

Effect on speed of sound wave:

speed of sound increased when temperature and humidity increased, but it remain constant when pressure change. if temperature increase 1C the speed increase by 0.61 m/s.

Characteristics of sound waves:

• Intensity of sound: amount of energy passing per unit area, SI unit watt/m^2. Intensity inversely proportional to the square of the distance of point from the source. and directly proportional to square of amplitude of vibration, frequency and density of the medium.
• Loudness: depends upon intensity of sound, unit is bel another unit is decibel(equal to 1/10 bel), another unit is phon.
• Pitch: define sharpness of sound, higher the frequency higher will be pitch.
• Echo: sound wave received after being reflected from a high tower mountain, minimum distance should be 16.6 m or 17 .

** Due to refraction, sound is heared at longer distances in night than in day.

Interference of sound: Superposition of two sound waves of same frequency.

• Constructive interference: two waves meet at point in same direction, intensity of sound waves is maximum at that point.
• Destructive interference: two waves meet at point in opposite direction, intensity of sound waves is minimum at that point.

Stationary wave: 

When two progressive wave of same type( both longitudinal or transverse) having the same amplitude and same time period/frequency/wavelength travelling with same speed along the same straight line in opposite direction, superimpose, a  new set of waives are formed which are called stationary or standing waves.

Doppler effect: if there is a relative motion between source of sound and observer, the apparent frequency of sound heard by observer is different from the actual frequency of sound emmited by the source,

Mach Number: ratio of speed of source of sound to the speed of sound in the same medium under the same condition of temperature and pressure.

Mach Number>1, body is called supersonic, >5 hypersonic, <1 subsonic.

Shock waves: A body moving with supersonic speed in air leaves behind its conical region of disturbance which spread continuously.

Bow wave: shock waves in water produced by motor boat.