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Sound and Light

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Sound and Light CHAPTER 15 – PowerPoint PPT presentation

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Title: Sound and Light


1
Sound and Light
  • CHAPTER 15

2
All sound waves
  • Are caused by vibrations

3
All sound waves
  • Are longitudinal waves

4
All sound waves
  • Require a medium -- solid, liquid, or gas.

5
The speed of sound
  • Depends on the medium and temperature
  • Fastest in most solids
  • (except ones like rubber that DAMPEN or
    weaken the sound waves -- these make good
    soundproofing materials)

6
The speed of sound is
  • Slowest in gases
  • The colder the gas,
  • the slower the speed
  • Speed of sound in room temperature air 346
    m/s (760 mi/hour)

7
Why does sound travel fastest in solids?
  • The molecules are closer together than in a
    liquid or gas so they pass on the vibrations more
    quickly

8
Loudness of sound depends on wave intensity
  • Intensity in turn is determined by the amplitude
    and distance from the source of the sound.

9
Intensity
  • Increases when amplitude increases
  • Decreases when amplitude decreases

10
Intensity increases as distance from source
decreases
  • Louder when closer because waves have spread out
    less

11
Loudness is measured in decibels
  • Logarithmic scale --
  • 70 decibels is twice
  • as loud as 60

12
Frequency determines pitch.
  • Higher frequency higher pitch
  • Lower frequency lower pitch

13
Beat Frequencies
  • Interference of two or more frequencies to form a
    new wave
  • Frequencies must be close to one another but not
    the same

14
Doppler effect
  • Frequency (and pitch) go up when source of sound
    is approaching because wavelength is shortened
  • Go down when source is retreating

15
Resonance
  • Tendency of an object to vibrate with larger and
    larger amplitudes
  • Examples
  • Opera singer breaking a glass
  • Pushing a kid on a swing
  • Running fingers on rim of a glass

16
Sonar
  • Measures distance by measuring time for sound
    wave to reflect off a surface, calculated
    distance using d v x t

17
Range of human hearing
  • 20Hz to 20,000 Hz

18
Ultrasound Frequency too high for us to hear
  • Can be used in sonar systems
  • Above 20,000 Hz

19
Infrasound
  • Frequencies that are too low to be heard by
    humans
  • Below 20 Hz
  • Examples
  • Earthquakes
  • Tornadoes
  • Storms at sea

20
Light
  • Sometimes acts
  • like a wave
  • Sometimes acts
  • like a particle

21
Light acts like a wave when it
  • Reflects
  • Refracts
  • Produces interference

22
Light acts like a particle when it
  • Travels without a medium
  • Delivers packets of energy (photons) to solar
    collectors or chlorophyll

23
The energy of light
  • Is proportional to its frequency
  • Gamma rays have the most energy because they have
    the highest frequency.

24
The speed of light
  • Depends on the medium
  • In a vacuum, the speed 3 X 108 m/s.
  • This speed is known as c
  • (as in Emc2).

25
Lights brightness depends on wave intensity.
  • Wave intensity decreases when amplitude decreases
  • Increases when amplitude increases

26
Intensity increases as distance from source
decreases
  • brighter when closer because waves have spread
    out less

27
Electromagnetic spectrum
  • Light at all possible energies, frequencies, and
    wavelengths
  • Entire spectrum given off by sun and other stars

28
Electromagnetic spectrum
29
Radio waves
  • Longest wavelength, least energy
  • Used in communication and radar

30
microwaves
  • Next longest waves
  • Used in cooking, communication

31
Infrared waves
  • Thermal energy -- heat

32
Visible light
  • Red is longest wavelength of visible light
  • Violet is shortest

33
Ultraviolet (UV) light
  • 9 of suns energy
  • Can cause sunburn, cancer
  • More dangerous than visible light because it
    has a shorter wavelength

34
X-rays
  • Shorter wavelength than UV light, so more
    dangerous
  • Used in medicine, but can disrupt DNA so
    must limit exposure

35
Gamma rays
  • Shortest wavelengths, so most energy (and most
    dangerous)
  • Rays can be focused to kill cancer
  • Given off by radioactive materials

36
Reflection
  • Light bouncing off a surface

37
Rough surfaces scatter the light they reflect
  • so they look dull, not shiny.

38
Smooth surfaces reflect the light in the same
direction
  • so they are shiny and can reflect an image.

39
Polarization
  • Filtering of light

40
Curved mirrors distort images, because different
parts of the mirror reflect the light in
different directions.
41
Objects have the color of the wavelength they
reflect.
42
Fiber optics use internal reflection to transmit
light along the length of the fibers.
  • This is more efficient than transmission through
    metal wires.

43
Refraction of Light
  • Light waves can bend (refract) when they pass
    from one medium into another.
  • The waves bend because the new medium changes the
    waves speed.

44
Refraction of light
  • The bending of light waves changes the apparent
    position of objects.

45
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46
Because lenses diffract light, they can
  • magnify images
    (microscope, magnifying glass)
  • focus images (eye, telescope).
  • Correct the poor focus of a near- or far-
  • sighted eye (glasses).

47
Prisms separate light into its component colors.
  • This happens because the different colors travel
    at different speeds and therefore bend different
    amounts. (Red is fastest and bends the least, so
    it appears at the top of a rainbow.)

48
In rainbows, water droplet act as prisms.
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