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Waves and wave motion

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Waves Sound Light Water Radio Seismic. ... Properties of waves 4 Interference occurs when waves from two sources meet to produce a wave of different amplitude. – PowerPoint PPT presentation

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Title: Waves and wave motion


1
Waves and wave motion
2
Can you think of some examples of waves?
3
Waves
  • Sound
  • Light
  • Water
  • Radio
  • Seismic.

4
What is the function of a wave?
  • A wave is a means of transferring energy from one
    place to another

5
TYPES OF WAVES
  • Waves are classified into different types
    according to their natures

6
Wave Types
Mechanical Electromagnetic
e.g. Water waves, waves on a rope, sound e.g. Radio, X-Rays, Light
Must have a substance to travel through Cannot travel in a vacuum Does not need a substance to travel through but can travel through various substances Can travel in a vacuum
Vibrations passed on from molecule to molecule Travel at very fast speed in a vacuum 3 108 m/s
7
Travelling Waves
  • Waves that travel from one place to another
  • e.g. Waves on rope
  • e.g Waves on water
  • e.g. compression waves on spring

8
Compression and Rarefraction
9
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10
Longitudinal wave
11
Types Of Waves
12
TRANSVERSE
A wave where the direction of the vibration is
perpendicular to the direction in which the wave
travels
LONGITUDINAL
A wave where the direction of the vibration is
parallel to the Direction in which the wave
travels.
13
Transverse Waves
  • Transverse waves
  • A transverse wave is a one in which the direction
    of vibration is perpendicular to the direction of
    propagation.
  • Examples
  • Light waves.
  • Radio waves.
  • Waves on a rope.
  • Water waves

14
Longitudinal Waves
  • Longitudinal Waves
  • A longitudinal wave is one in which the direction
    of vibration is parallel to the direction of
    propagation.
  • Examples
  • Sound waves in a solid, liquid or gas.
  • Compression waves on a spring.
  • Seismic waves.

15
Wave..........
  • The wavelength of a wave is the distance from
    one point on the wave to the corresponding point
    on the next cycle.

16
  • The frequency of a wave is a measure of the
    number of oscillations (vibrations) of the wave
    per second.
  • The periodic time of a wave (T) is the time taken
    for one complete cycle.

17
Symbols and units
Variable Symbol Unit Symbol for Unit
Frequency f Hertz Hz
Wavelength ? (lamda) metre m
Velocity v (or c for light) metre/second m/s
Time T second s
18
The relationship between frequency, velocity and
wavelength
  • c f ?
  • or
  • v f ?

19
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20
Properties of waves
  • 1. Reflection Reflection is the bouncing of a
    wave off an object.

21
Properties of waves
  • 2 Refraction is the bending of a wave as it
    travels from one medium to another. Note that
    when a wave travels from one medium to another
    its frequency does not change.

22
Properties of waves
  • 3. Diffraction is the spreading of waves around a
    slit or an obstacle.
  • This effect is only significantly noticeable if
    the slit width is approximately the same size as
    the wavelength of the waves.

23
Properties of waves
  • 4 Interference occurs when waves from two sources
    meet to produce a wave of different amplitude.

24
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.


25
Two types of interference
Constructive Interference Destructive
Interference
26
Constructive Interference
  • Constructive Interference occurs when waves from
    two coherent sources meet to produce a wave of
    greater amplitude.
  • (Constructive interference occurs when the crests
    of one wave are over the crests of another wave).

27
Destructive Interference
  • Destructive Interference occurs when waves from
    two coherent sources meet to produce a wave of
    lower amplitude.
  • (Destructive interference occurs when the crests
    of one wave are over the troughs of the second
    wave. This will happen if one wave is half a
    wavelength out of phase with respect to the
    other).

28
5. Polarisation
  • Only TRANSVERSE waves can be polarised.
  • To polarise a wave means to make it vibrate in
    one plane only
  • horizontally plane polarised or
  • vertically plane polarised

29
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30
Polarised sunglasses
31
The frequency of a wave is a measure of the
number of oscillations (vibrations) of the wave
per second. Another way of defining frequency of
a wave is to say it is the number of waves that
pass a fixed point per second. T 1/f
32
  • The relationship between periodic time and
    frequencyT 1/f
  • or
  • f 1/T

33
Standing waves
A standing wave/stationary wave is the result of
two waves of the same wavelength, frequency, and
amplitude travelling in opposite
directions through the same medium.
34
  • From the diagram we can see that
  • The distance between two consecutives nodes is
    ?/2
  • The distance between two consecutive antinodes is
    ?/2
  • The distance between an anti-node and the next
    node is ?/4

35
The Doppler Effect
  • The Doppler effect is the apparent change in
    frequency of a wave due to the motion of the
    source or the observer.
  • The observed frequency is higher when the source
    and observer are getting closer.
  • The observed frequency is lower when the source
    and observer are getting farther away.

36
  • The distance between successive crests is the
    constant and so the number of crests passing a
    point in one second is the frequency of the wave.
  • These waves will pass an observer in equal
    intervals of time.
  • This means that the wavelength, and the
    frequency, will be constant.

Consider a source S emitting a wave with crests
1, 2, 3 as shown.
37
In this case the source is moving to the right
while emitting the waves.
  • The result is that
  • Ahead of the moving source the crests are closer
    together than crests from the stationary source
    would be. This means that the wavelength is
    smaller and the frequency is greater.
  • Behind the moving source, the crests are further
    apart than crests from the stationery source
    would be. This means the wavelength is greater
    and so the frequency is less.

38
Formula f apparent frequency f actual
frequency c speed of the wave u speed of the
moving source
39
Example of the Doppler Effect
The noise from a racing car as it approaches and
then moves away from an observer is an example
of the Doppler effect. This is NOT an
APPLICATION of the Doppler effect.
40
Applications of the Doppler Effect
  • Police speed traps
  • Measuring the red shift of galaxies in astronomy

41
Doppler shift gives radial velocity
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