Introduction to WavesIntroduction to Waves

Definition of waveDefinition of wave

• A periodic disturbance which travels through a medium from one point in space to the others.

Wave motion means the propagation of waves through a medium.

Wave motion appears in almost every branch of Physics.

Basic properties of wavesBasic properties of waves :• Energy is transferred from one place to another in a

wave motion.• Motion of the medium (particles of the medium) is

usually periodically vibratory.• Only the shape or form of wave travels, not the

medium.

TYPES OF WAVESTYPES OF WAVES

Waves Waves are classified into different types according to their nature:

T ra ns ve rs e w a ve s L o ng itud ina l w a ve s

Mechanical w aves

T ra ns ve rs e w a ve s

Elec tromagnetic w aves

WA V E S

Mechanical Waves• A material medium is necessary for the transmission for

mechanical waves. Mechanical waves cannot travel through vacuum.

• A disturbance is transmitted from one layer to the next through the medium.

Examples: Water waves, sound, vibration of spring, etc.

Transverse Waves (Mechanical)

• The waveform appears in the shape of sine curve.• A wave in which the motions of the matter particles are

perpendicular to the direction of propagation of the wave itself.

Examples: Water waves, pulse in a stretched string.

Longitudinal Waves (Mechanical)

• When energy travels through a medium (matter), matter is compressed in the forward direction.

Examples: Sound, or a spring oscillating up and down.

Electromagnetic Waves• Can travel through vacuum or a medium

• Disturbance of electric and magnetic fields travelling through space.

• All electromagnetic waves are transverse waves.

X-rays, radio waves, micro-waves,visible light, etc.

• The amplitude is the maximum displacement of the medium from its equilibrium position.

• The wavelength () is the minimum distance between two points which are in phase.

• The frequency (ƒ) is the number of complete oscillations made in one second. Unit: Hertz (Hz)

• The period (T) is the time taken for one complete oscillation. It is related to frequency by T = 1/ƒ Unit: seconds

The Wave EquationThe Wave EquationThe wave velocity is the distance traveled by the wave in one second ……....

The wave velocity (v) is related to frequency and wavelength.

v = ƒv = ƒ

Using the Wave EquationUsing the Wave EquationExample :

A travelling wave of wavelength 0.6m moves at a speed of 3.0 m/s. What is the period of this wave ?

The answer is…

Then the period of this wave is ???Period T = 1/ƒ T = 1/5.0 or 0.2 s

Now you know = 0.6 m, v = 3.0 m/s Can you find the frequency of this wave……

By using the wave

equation, v = ƒ 3.0 = ƒ(0.6) i.e ƒ = 5.0 Hz

• Transmission of energyTransmission of energy• ReflectionReflection• RefractionRefraction• DiffractionDiffraction• Interference Interference

Let’s take water waves as an example to study the characteristics of waves….

The behavior of water waves demonstrates all these characteristics……..

characteristics

A travelling wave is reflectedreflected when it hits a barrier.

This phenomenon can easily be observed when a travelling waterwave hits a reflector in the ripple tank.

Reflection of Waves

Reflectedwaves

Reflectedwaves

Reflector

Refraction of WavesRefraction of Waves

- The speed of a water wave increases with depth. This change in speed is accompanied by refraction.

This effect is a consequence of the wave equation, v = ƒ.Since ƒ is constant, a decrease in v produces a decrease in .

Diffraction of Waves

When a travelling water wave hits an obstacle, the wavefront spreads out round the edge and becomes curved. This phenomenon refers to diffraction..

The wavelength of the wave is not changed in diffraction.

Interference of Waves

When two or more waves propagating in the same medium meet at the same point, interference is said to occur. A stable interference pattern can be observed when two water waves of same frequency meet one another in a ripple tank.

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