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Transcript
WAVES
Wave motion allows a transfer of
energy without a transfer of
matter
TRANSVERSE WAVES
• A transverse wave causes the particles in
the medium to oscillate perpendicularly to
the direction of wave travel
Direction
of wave
Crest
Mean position
Trough
LONGITUDINAL WAVES
• A longitudinal wave causes the particles in
the medium to oscillate in the direction of
the wave.
Rarefaction
Compression
Rarefaction
TRANSVERSE
WAVE eg light
LONGITUDINAL
WAVE eg sound
Particle
motion
Direction
of wave
Direction
of wave
Particle
motion
Particles move to and fro
at 900 to the direction of
the wave in a transverse
wave.
Particles move to and fro
in the direction of the
wave in a longitudinal
wave.
• Frequency
The frequency of a wave is the number of
waves generated by a source in a second.
– The symbol for frequency is f
– Its unit is Hertz (Hz) or cycles per second
• Amplitude
Amplitude is the maximum displacement of
a particle from its mean position
– The symbol for amplitude is A
– It is measured in metres (m)
Speeds of waves
s
v
t
• With sound when travelling within a
medium, the wave speed is constant, and
independent of wave frequency.
What will the time delay in hearing the sound from a brass
band for an observer standing 660 m away? Assume the light
arrives instantaneously and sound travels at 330 m/s.
Wavelength
• The distance between each cycle of the wave is called the
wavelength.
• Particles in phase
– Particles travelling at the same speed in the same
direction are said to be in phase
• The wavelength of a wave is the distance between two
successive points in phase.
Direction
of wave



• Wavelength is given the Greek symbol
lambda
• Wavelength is a distance, measured in m

PERIOD
The period of a wave is the time taken for one
wave to pass a given point.
Period is given the symbol T
It is measured in s
1
T
f
The frequency of a wave is the number of waves passing a
point per second. Its unit is Hertz (Hz) or cycles per second.
If 2 pass each second its frequency is 2 Hertz
The wavelength is distance between each cycle of the wave (the
distance between consecutive crests)
If the wavelength is 30 cm



The wave speed or velocity is how fast the wave is travelling.
http://www.crocodileclips.com/absorb/AP4/sa
mple/DJFPh065.html
Then the velocity of the wave is 2 x 30 = 60 cm/s
Wave speed = frequency x wavelength
P 669-671
THE WAVE EQUATION
v  f
Where
v = wave speed
f = frequency
 = wavelength
The electromagnetic spectrum consists of transverse
electric and magnetic fields varying at right angles to
each other. The entire pattern moves in a direction
perpendicular to both E and B fields.
7.5 x 10-7m 7.0 x 10-7m
6.0 x 10-7m
5.0 x 10-7m
4 x 10-7m
Properties of all
electromagnetic waves
1.They transfer energy from one place to another
2.They are all transverse waves
3.They can be reflected, refracted, diffracted
4.They can all travel through a vacuum
5.They all travel at 3.00 x 108 m/s in a vacuum
6.The shorter the wavelength (the higher the
frequency), the more penetrating they become
and the more dangerous they are