General Properties of WAVE

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General Properties ofWAVE

• Sec 3 Exp
• Science PHYSICS

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What is a Wave?

• Wave is a mechanism that carries energy from one
  point to another.
• A wave is created by vibrations or oscillations
  of objects or substances.
• Waves carry energy from one point of vibrations
  or oscillations to another.

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2 Types of Waves

• TRANSVERSE
• LONGITUDINAL

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Transverse waves

• Waves that travel in a direction perpendicular to
  the direction of vibration of particles.
• This means that particles of transverse wave only
  moves up and down, while wave travel sideways.
• Some examples are rope waves, water waves, light
  waves and radio waves.

Direction of wave
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Transverse Wave
Transverse wave in air. Direction of wave is from
left to right. Notice how the air particles are
vibrating with respect to the direction of wave
motion. The air particles are just vibrating up
and down about their fixed positions as the wave
moves from left to right.
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Longitudinal Waves

• Waves that travel in the same direction as the
  direction of vibration of particles.
• Particles of longitundinal waves move
  side-to-side in a direction parallel to direction
  of wave.
• Some examples are sound waves and waves produced
  by springs.

Direction of wave
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Longitudinal Wave
Longitudinal wave in air. Direction of wave is
from left to right. Notice how the air particles
are vibrating with respect to the direction of
wave motion. Although it appears at first glance
that groups of air particles are moving from left
to right, if you look closely, the air particles
are in fact just vibrating about a fixed position.
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Key point 1! for ALL wave motion

• During wave motion, the particles are NOT
  transferred from one point to another.
• They just vibrate about their fixed or neutral
  position.

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Terms used in waves

• Crests
• Troughs
• Displacement
• Amplitude

• Wavelength
• Frequency
• Period
• Wavefront

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Crests
Displacement /m
wavelength
amplitude
Distance/m
amplitude
wavelength
Troughs
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Properties of Wave Motion

• Crest The highest point of a transverse wave.
• Trough The lowest point of a transverse wave.
• Amplitude Maximum displacement from rest
  or central position. Unit meter (m).
• Displacement has positive and negative values.
  Normally when particles moves upwards its
  positive. When downwards its negative.

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Describing a wave

• Wavelength Shortest distance between two ( ?
  ) points on the wave that are in phase.
  Unit meter (m)
• Distance between two troughs.
• Distance between two crests.
• (In phase both particles move in the same
  direction, at the same speed and have the same
  displacement from rest position.)

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Describing a wave

• Frequency Number of complete waves ( f
  ) produced in one second.
• Unit Hertz (Hz)
• Period Time taken to produce one ( T )
  complete wave. Unit seconds (s)
• Inverse of frequency
• (i.e. T 1 / f )

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Describing a wave

• Wave speed The distance travelled by a wave
  (v) in one second.
• SI unit m /s
• Wavefront An imaginary line on a wave that
  joins all points which have the same
• phase of vibration.

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Quick Check

• A boy sings as he plays with a rope. He vibrates
  one end of the rope up and down repeatedly, while
  the other end is fixed to a wall.
• What type of wave is obtained in the rope?
• Transverse
• Define transverse wave.
• A wave where its particles vibrate in a
  perpendicular direction to that of the direction
  of wave.
• (c) The sound that the boy made while singing is
  an example of (transverse, longitudinal) wave.

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Quick Check

• Give one example of a longitudinal wave.
• Sound wave
• 3. Label the wave terms crest, trough,
  wavelength and amplitude in the
  displacement-distance graph below of a transverse
  wave.

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Relationship between velocity, frequency and
wavelength

• Speed of a wave frequency of wave X
  wavelength of the wave
• In symbols,
• v f ?

v wave speed/velocity (m/s) f frequency
(Hz) ? wavelength (m)
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The frequency period equation
f 1/T

• Knowing frequency, we can find the period of a
  wave.
• Similarly, if we know the period, we can find the
  frequency of the wave.

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The Ripple Tank

• The ripple tank allows us to observe the
  behaviour of waves easily.
• Basically waves behaves similar to that of light
• Waves reflect
• Waves refract

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Measuring wavelength
1 wavelength
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Displacement vs distance Graph

• Waves can be plotted on a displacement vs
  distance graph.
• The displacement refers to displacement of
  particles, while distance refers to the distance
  of particles from a starting point.
• From this graph, we can find
• Wavelength
• Amplitude
• Distance of particles from a position

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Displacement /m
wavelength
amplitude
Distance/m
amplitude
wavelength
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Displacement vs time Graph

• Waves can be plotted on a displacement vs time
  graph.
• The displacement refers to displacement of
  particle just one particle, while time refers to
  the time of that same particle moves a particular
  displacement
• From this graph, we can find
• Period of wave
• Amplitude
• From period, we can calculate the frequency of
  the wave

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Displacement /m
period
amplitude
Time/s
amplitude
period
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Eg. Displacement vs time Graph

• A displacement time graph of a wave with
  wavelength 0.4m is shown.
• Calculate the frequency of the wave.
• Period of wave is 0.5 s
• So f 1/T 1/0.5 2 Hz
• (b) Calculate the speed of the wave.
• Speed frequency x wavelength 2 x 0.4
• 0.8m/s

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Displacement /m
0
0.25
0.5
0.75
Time/s
1.0
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Quick Check

• Calculate the wave speed of a wave of frequency
  500 Hz and a wavelength of 0.02 m.
• v 500 x 0.02 10 m/s
• Calculate the wavelength of a wave that has a
  frequency of 2kHz and speed of 5m/s.
• wavelength v/f 5/2000 0.0025 m

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Quick Check

• A wave of speed 330 m/s has a wavelength of 2m.
• Calculate the frequency of the wave.
• frequency v/wavelength 330/2 165 Hz
• (b) Calculate the period of the wave.
• period 1/f 1/165 0.006 s