8/7/2019 What is waves

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What is waves?Process of transferring energy from one

ocation to another which is produced by anscillating or vibrating motion.

xamples of wavesLight waves are produced as a result of

ibrations of electrons in an atomSound waves are produced by vibrating

mechanical bodies such as a guitar strings ortuning fork.Water waves are produced by a

isturbance on a still water surface

How do waves transfer energy?When energy is transferred by a wave

rom a vibrating source to a distanteceiver, there is no transfer of matteretween the two points.

When the string is shaken up and down, aisturbance moves along the length of thetring. It is the disturbance that moveslong the length of the string, not parts ofhe string itself.

Drop a stone in a quite pond. It will produce

wave that moves out from the center inxpanding circles. It is the disturbance that

moves, not the water. After the disturbanceasses, the water is where it was before the

wave was produced .

The string and water is the medium throughwhich wave energy travels.

The energy transferred from a vibratingource to a receiver is carried by aisturbance in a medium, not by matter

moving from one place to another within themedium

What is Transverse Wave?A transverse wave is a wave in which the

ibration of particles in the medium is atght angle to the direction of propagationf the wave.

The spring is moved sideways. The motion ofthe particles medium (spring) is at rightangles to the direction in which the wavetravels.Examples: water waves, light waves

What is Longitudinal Waves?+ A longitudinal wave is a wave which thevibration of particles in the medium is along(parallel to) the direction of propagation ofthe wave.

The slinky spring moves backwards andforwards to produce a transverse wave. Theparticles of the medium (spring) move alongthe direction of the wave. The wave that

travels along the spring consists of a seriesof compression and rarefaction.Examples: soundswaves.

What is a ripple tank?

The phenomenon of water waves can beinvestigated using a ripple tank.The water waves are produced by a vibrating

bar on the water surface.The tank is leveled so that the depth ofwater in the tank is uniform to ensure waterwaves propagate with uniform speed.

The water acts as a lens to produce apattern of bright and dark regions on apiece of white paper placed under the tankwhen light passes through it.Water waves have crests and troughs.A crest is the highest position of the waveacts as a convex lens, whereas a trough isthe lowest position acts as a concave lens.Light rays from the lamp on top will focusonto the white screen below. The bright

lines correspond to the crests, and the darkline

correspond to the troughs.

What is meant by a wavefront?

+ Lines joining all the points of the samephase are called wavefronts.+ The wavefronts of a transverse wave andlongitudinal wave are perpendicular to thedirection of propagation of the waves.

Plane wavefronts

2. Circular wavefronts

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Describing Waves

Vibration/OscillationThe movement from one extreme position tohe other and back to the same position.

Amplitude (a)The maximum displacement from its

quilibrium position.Amplitude relates to loudness in sound and

rightness in light. SI unit: meter, m

Wavelength ()The distance between two adjacent points

f the same phase on a wave.x.The distance between two successiverests or two successive troughsThe distance between two successiveompressions or two successive rarefactionsn a sound wave.

eriod (T)The time taken for an oscillation to

omplete one cycle.I unit is second (s).

Frequency, fThe number of waves produced in one

econd.

SI unit is Hertz (Hz)

Wave Speed (v)The speed of a wave is the measurement ofhow fast a crest is moving from a fixedpoint.SI unit is ms-1.

Relation between frequency and period:

f = 1/T

The relationship between speed, wavelengthand frequencyVelocity = wavelength x frequencyv = f

Displacement-time graph

Displacement-distance graph

Velocity , v = f

What is damping?+ Damping is the decrease in the amplitudeof an oscillating system when its energy isdrained out as heat energy.+ The amplitude of an oscillating system willgradually decrease and become zero whenthe oscillation stops.

What causes damping?1. External damping of the system is the lossof energy to overcome frictional forces orair resistance.2. Internal damping is the loss of energy dueto the extension and compression of themolecules in the system.

A graph to show damping

External Force+ To enable an oscillating system to go oncontinuously, an external force must beapplied to the systemForce oscillation+ The external force supplies energy to thesystem. Such a motion is called a forcedoscillationNatural frequency+ The frequency of a system which oscillafreely without the action of an externalforce is called the natural frequency.