4 Introduction to Waves

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4 Oscillations ans Waves (10 h)


Kari Eloranta

2013Jyvskyln Lyseon lukio

International Baccalaureate

February 6, 2013

Kari Eloranta 2013 4 Oscillations ans Waves (10 h)


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4.4 Wave characteristics

4.4 Wave Sources

Figure : When a stick is dipped into the water, a series of circular disturbances are created (Roger McLassus).



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4.4 Wave Sources

A periodic oscillator can act as a

wave source.If the end of a rope is connectedto an oscillator (such as a moving

hand), continuous pulses travel onthe rope forming a wave.

Oscillating electrons create

electromagnetic waves in antennae.Human vocal cords, and musicalinstruments, create sound waves.

Figure : Vibrating air colums in musical instrumentscreate sound waves ( Infrogmation).


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4.4 Travelling Waves

Wave Pulse

Wave pulse is a traveling disturbance in a medium.Travelling WaveTravelling wave is a series of travelling wave pulses.

Examples of travelling waves include water waves, sound waves, andelectromagnetic waves.

Water and sound waves are examples of mechanical travelling waves, where

disturbations travel in a medium.Electromagnetic waves do not need a medium in which to travel. The speed ofelectromagnetic waves in vacuum is c= 3.00108m s1.


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4.4 Wavelength of a Wave

0.10

0.20

0.30

0.100.20

0.30

0.5 1.0 1.5 2.0 2.5 3.0

x

cm

ycm

wavelength

WavelengthWavelength is the shortest distance along the wave between two points in phase

with one another (OR: distance travelled by the wave in one period).




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4.4 Amplitude A of a Wave

0.10

0.20

0.30

0.10

0.20

0.30

0.5 1.0 1.5 2.0 2.5 3.0

x

cm

ycm

amplitude A= 0.30m

amplitude A= 0.30m

AmplitudeAmplitude is the greatest displacement from the equilibrium position.

In the figure above, the amplitude is A= 0.30m from the x-axis.




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4.4 Period T of a Wave

0.10

0.20

0.30

0.100.20

0.30

0.5 1.0 1.5 2.0 2.5 3.0

t

s

ycm

period T

Period T of a WavePeriod is the time taken for one complete oscillation (OR: time taken for one cycle

to pass a given point).




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4.4.3 Mechanical Longitudinal Wave

Mechanical Longitudinal WaveA longitudinal wave is a wave in which the direction of motion of the energytransfer is parallel to the direction of motion of the particles of the medium.

Sound waves are an example of mechanical longitudinal waves.

Longitudinal waves can travel in all types of medium: gas, liquid and solid.




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4.4.3 Mechanical Transverse Wave

Mechanical Transverse WaveTransverse wave is a wave in which the direction of motion of the energy transferis perpendicular to the direction of motion of the particles of the medium.

Traveling pulses in a rope, or S-type Earth quake waves are examples ofmechanical transverse waves.

Mechanical transverse waves cannot exist in gases, because there are nointermolecular forces that could produce such motion.

Electromagnetic waves are non-mechanical transverse waves, in which theelectric field oscillates at right angles to the direction of the wave.




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( )

4.5 Wave Properties

4.5.2 Snells Law

A wave comes from medium 1, and refracts to medium 2. Frequency of the wavestays the same, but velocity changes.

1

2

refractive index n1, wave speed v1wavelength 1, frequency f


According to Snells Law, the ratio of refractive indices is

n1n2= sin2

sin1= v2

v1= 2

1




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( )

4.5 Wave Properties

4.5.2 Snells Law

A wave comes from medium 1, and refracts to medium 2.

1

2


refractive index n2, wave speed v2

wavelength 2, frequency f

According to Snells Law, the ratio of refractive indices is

n1

n2=

cv1cv2

=c

v1v2

c

=v2

v1=2

1

=sin2

sin1

where c is the speed of light in vacuum. Kari Eloranta 2013 4 Oscillations ans Waves (10 h)

4 Introduction to Waves

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