Wave

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Wave

• S.5B HUNG WING YAN (14)
• LEUNG YI LAM (23)

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Content

• Wave Motion
• Water Waves
• Light Waves
• E.M Waves
• Sound Waves

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Wave Motion

• Mechanical waves require a material medium to
  travel (air,water, ropes). These waves are
  divided into three different types.
• Types of Waves
• Transverse waves
• Longitudinal waves
• Surface waves
• Electromagnetic waves
• Matter waves

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Transverse waves

• A transverse waves is one in which the
  vibrations of the medium particles are at right
  angles to the direction of travel of the wave
  motion

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Longitudinal waves

• A longitudinal waves is one in which the
  vibrations of the medium particles are at
  parallel to the direction of travel of the wave
  motion

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Standing Waves

• Fixed one end of a long string onto a wall and
  shake the other and continuously. By adjusting
  the rate of shaking, some vibrating to move
  backwards or forwards. This is called standing
  waves or stationary wave.

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Measuring Waves

• Any point on a transverse wave moves up and down
  in a repeating pattern.  
• The shortest time that a point takes to return to
  the initial position (one vibration) is called
  period, T. In this example, every vibration is
  marked with a short pause.

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• The number of vibrations per second is called
  frequency and is measured in hertz (Hz). Here's
  the equation for frequencyf 1 / T
• The shortest distance between peaks, the highest
  points, and troughs, the lowest points, is the
  wavelength,

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• By knowing the frequency of a wave and its
  wavelength, we can find its velocity. Here is the
  equation for the velocity of a wave
• However, the velocity of a wave is only affected
  by the properties of the medium. It is not
  possible to increase the speed of a wave by
  increasing its wavelength. By doing this, the
  number of vibrations per second decreases and
  therefore the velocity remains the same.

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• The amplitude of a wave is the distance from a
  crest to where the wave is at equilibrium. The
  amplitude is used to measure the energy
  transferred by the wave. The bigger the distance,
  the greater the energy transferred.

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Example

• A radio wave has a frequency of 93.9 MHz (93.9
  106 Hz). What is its period? f 93.9 106 Hz
  f 1 / T T 1 / f T 1 / 93.9 x 106 Hz T
  1.06 x 10-8 s

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Moving from one medium to another

• Once a wave (incident wave) has reached the end
  of a medium, part of the energy is transferred to
  the medium that is immediately next to it
  (transmitted wave) and part is reflected backward
  (reflected wave).
• The energy transferred depends on the difference
  between the mediums. If there is a significant
  difference, almost all the energy will be
  reflected. If the mediums are similar, most of
  the energy will be transferred. However, the
  reflected waves will be inverted if the medium
  that comes next is more dense or it won't be
  inverted if the medium is less dense

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Collision of waves

• When two waves traveling in opposite directions
  through the same medium collide, the amplitude of
  the resulting wave will be the sum of the two
  initial waves. This is called interference and
  there are of two types 
• Constructive interference
• Destructive interference

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Water Waves

• A dot vibrator
• produces
• circular waves.
• A bar vibrator
• produces plane
• waves.

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Reflection of Water Waves at Straight Line

• Reflection of water
• waves obeys the law of reflection,
• ANGLE OF INCIDENCE i
• ANGLE OF INCIDENCE j

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Refraction of Water Waves

• Refraction takes place when there is a change in
  the waves speed when the waves travel across a
  boundary between two different depths.
• When the water enter a shallow water region, its
  speed and hence its wavelength decreases.

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Diffraction of Water Waves

• Diffraction of water waves refers to the
  spreading out of waves when the waves travel
  round the edge of obstacle or passing through a
  silt.
• There is no change in v,f and of the
  diffracted waves.

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• 2. For a given gap size, the amount of
  diffraction increase with longer wavelength
• 3. For a given wavelength, the amount of
  diffraction increase with smaller wavelength

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Interference of Water WavesInterference is the
superposition of two wave frequency and
amplitude.

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Interference of Water Waves
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Constructive interference

• Constructive interference is when the
  amplitudes of the initial waves are in the same
  direction. The resulting wave will be larger than
  the original waves. The highest point of a
  constructive interference is called an antinode

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Destructive interference

• Destructive interference is when the amplitudes
  of the initial waves are opposite. The amplitude
  of the resulting wave will be zero. The point in
  the middle of a destructive interference is
  called a node and it never moves.

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Light Waves

• Of all the electromagnetic waves, light is the
  only portion of waves that can be detected by the
  human eye.
• Colors Red, green and blue are known as primary
  colors, because when they are added together
  white light is formed.
• By mixing primary colors in pairs
• we obtain secondary colors. Red
• and green produce yellow. Blue
• and red produce magenta, and
• blue and green produce cyan.

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Light Waves

• Light is one of the electromagnetic waves ( EM
  Waves ) . Light rays show reflection and
  refraction. But these two properties are not
  sufficient to prove that light is wave. In
  1801,Thmas Wong demonstrated the interference of
  light in his Double-Slit Experiment and the wave
  nature of light established

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E.M Waves
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Sound Waves

• They are longitudinal waves
• produced by variations in air
• pressure.A vibrating source
• pushes molecules in air back
• and forth, creating areas of
• compression and rarefaction. When a molecule
  moves, it collides with the next one and makes it
  move too. The energy of a sound wave travels away
  from the source trough a series of molecule
  collisions parallel to the. direction of the
  wave.
• Sound cannot travel through
• a vacuum.

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• Sound waves can also travel trough liquids and
  solids. The velocity of a sound wave depends on
  the temperature of the medium and its elasticity
  (more elasticity means that molecules will move
  easily). Through air, sound waves travel at 343
  m/s. Actually, sound waves move faster through
  liquids and solids than through gases. 

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Measuring sound waves

• The human ear is able to feel frequencies between
  20 Hz to 15 000 Hz, depending on the age of the
  person. Sound waves with a frequency above 20 000
  Hz are called ultrasonic waves.  The amplitude
  or volume of a sound wave is the amount of
  pressure exerted by a sound source to air
  molecules. The higher the pressure, the harder
  the molecules will collide and the farther the
  wave will travel.

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• Pitch
• The frequency of a sound wave is called pitch. In
  music, different pitches (C, D, E, etc.) are
  represented by notes. Its note depends on the
  frequency of the sound. The higher frequency, the
  higher the pitch.

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• The loudness of a note depends on the amplitude
  of the sound. The greater the amplitude, the
  louder the sound

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• Quality
• The quality of a note depends on its waveform.
  Although different musical instrument may produce
  waves with same frequency, their waveforms may be
  different.

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a.An echo-location system, called sonar,
is used by ships and boats toi. detect large
object under water,ii. detect shoals of
fishiii. to measure the depth of the sea.The
depth of sea, dvt/2where v is the speed of
sound in water and t is the time interval for the
reflected ultrasonic wave to be detected.

• Ultrasonic

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• b. Diagnosis in medicine
• c. Autofocusing in cameras
• d. To detect flaws and cracks in metal product
• e. To clean small delicate object e.g spectacles
  and jewellery
• f. Used in remote control systems e.g hi-fi sets
  and televisions

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• END