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4 Oscillations ans Waves (10 h)
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 Oscillations ans Waves (10 h)
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 Oscillations ans Waves (10 h)
4.4 Wave characteristics
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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O ill i W (10 h)
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4.4 Wave characteristics
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 Wave characteristics
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 Oscillations ans Waves (10 h)
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4.4 Wave characteristics
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 Oscillations ans Waves (10 h)
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4.4 Wave characteristics
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 Oscillations ans Waves (10 h)
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4.4 Wave characteristics
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 Oscillations ans Waves (10 h)
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4.4 Wave characteristics
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
refractive index n2, wave speed v2wavelength 2, 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 n1, wave speed v1wavelength 1, frequency f
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)
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