Types of Waves (1) Mechanical waves and electromagnetic waves Some waves require a material substance called a medium through which to travel. Waves like this are called mechanical waves. Examples: water waves, sound waves and seismic waves etc. Electromagnetic waves require no medium through which to travel. Example: radio waves, microwaves and light etc.

Type of Waves (2) Transverse waves and longitudinal waves In transverse wave, the direction in which the disturbances take place is at right angles to the direction of propagation of the waves. In longitudinal wave, the disturbances take place in a direction parallel to the direction of propagation of the waves.

Type of Waves (3) Progressive waves and stationary waves A wave which transmits energy from the source to the space surrounding the source is called a progressive wave (travelling waves). In certain conditions, waves energy is localized. When this happens, the waves are called stationary waves (standing waves).

Comparison of stationary waves and progressive waves Travelling waves Waveform does not move, but has nodes at fixed places, energy is not carried away. Waveform moves through the medium, carrying energy, but not the medium, with it. The amplitude varies from zero at a node to maximum at an antinode. The amplitude is the same for all particles along the wave. All the particles between two adjacent nodes are in phase. Over one wavelength all particles have different phases.

Wave Equations In a sinusoidal wave, each particle undergoes simple harmonic motion about its equilibrium position.This gives the equation where  = 2 f or where k = 2π/λ

Variation of Displacement with Time Graph of the equation y t T 2T A

Variation of displacement with distance Graph of the equation y x λ 2λ A

Wave Function for a Sinusoidal wave (1) Mathematically the variable y depends on two variables x and t. So the combined equation is or

Velocity of Propagation of Mechanical Waves (1) It is usually found that the speed of a mechanical wave is affected by two factors. One of the factors is associated with the strength of the elastic coupling between particles in the medium through which the waves travels. The other factor is associated with the inertia of the moving particles.

Velocity of Propagation of Mechanical Waves (2) Equations giving the speed of different types of wave Transverse wave on string Transverse ripples on a pond Longitudinal wave on a spring Longitudinal wave on a rod Sound wave in a gas

Huygens’ Principle http://id.mind.net/~zona/mstm/physics/waves/propagation/huygens1.html Every point on a wavefront can be considered as a source of tiny wavelets that spread out in the forward direction at a speed of the wave itself. The new wavefronts is the envelop of all the wavelets – that is, the tangent to all of them.

Huygens’ Principle and the Law of Reflection B vt A’ B’ vt The angle of incidence=the angle of reflection http://home.a-city.de/walter.fendt/phe/huygenspr.htm

Huygens’Principle and the Law of Refraction B v1t B’ A’ A v2t Sin i/sin r = v1/v2 = 1/2

Phase Change on Reflection (1) http://surendranath.tripod.com/Twave/TwaveRefTran/TwaveRefTran.html Fixed end reflection There is a phase Change of  after reflection

Phase Change on Reflection (2) A wave travelling from a less dense medium to a denser medium

Phase Change on Reflection (3) Free end reflection No phase change occurs

Phase Change on Reflection (4) A wave travelling from a denser medium to a less dense medium

Phase Change on Reflection (5) Phase changes also occurs when longitudinal waves are reflected. Fixed end Free end R C R C C R R C

Uses of Reflected Waves Radar (Radio Detection And Ranging) Pulses of high-frequency radio waves are transmitted towards distant objects and their reflections are received between the transmitted pulse. Sonar (Sound Navigation And Ranging) Pulses of ultrasonic waved are transmitted towards under water objects, and their reflected pulses are detected. Ionospheric Waves Radio waves from the transmitter travels through air and is reflected by the ionosphere. http://www.pbs.org/wgbh/nova/lochness/sonar2.html

Uses of Radar Detect the presence of an object at a distance Detect the speed of an object Map something-to create detailed topographic maps of the surface of planets and moons. http://www.howstuffworks.com/radar2.htm

Uses of Sonar Depth sounders Fish finders Side Scan sonar To measure the depth of the sea Fish finders To detect shoals of fish Side Scan sonar To map the ocean floor http://www.pbs.org/wgbh/nova/lochness/sonar.html

Atmospheric Windows to EM Radiation

Reflection of Radio Waves from the Ionosphere

Propagation of Radio Waves

Transverse waves Particles vibrate along a line which is perpendicular to the direction of travel of the disturbance.

Longitudinal Waves Particles vibrate along a line which is parallel to the direction of travel of the disturbance. Rarefaction Compression 

Stationary Waves  Nodes Antinodes A stationary wave doesn’t appear to be travelling. Nodes Antinodes 