The Electromagnetic Spectrum and Light

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Chapter 18

• The Electromagnetic Spectrum and Light
• (Sections 18.1-18.3 only)

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18.1 Electromagnetic Waves
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What Are Electromagnetic Waves?

• EM waves consist of changing electric fields and
  magnetic fields.
• EM waves carry energy from place to place.

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How are EM waves produced?

• When an electric field changes, so does the
  magnetic field.
• The changing magnetic field causes the electric
  field to change. When one field vibratesso does
  the other.
• EM waves are produced when an electric charge
  vibrates or accelerates. In other words it is
  produced in constantly changing fields.

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How are EM waves produced?

• Electromagnetic waves are produced when an
  electric charge vibrates or accelerates.

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How they travel

• EM waves can travel through a vacuum, or
• empty space, as well as through matter.
• This is called electromagnetic radiation.

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Did you know?

• The speed of light is constant in a vacuum.
• Speed of light (c) 3.00 x 108 m/s

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Wavelength and Frequency

• EM waves vary in wavelength and
• frequency despite traveling at the same
• speed.
• Speed of light (c) wavelength x frequency

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Quick Facts

• Speed 3.0 x 108 m/sec (speed of light)
• Wavelength varies
• Frequency varies
• Travels in a straight line (need satellites to
  account for this problem)
• Video Clip (328)

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18.2 Electromagnetic Spectrum
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Electromagnetic Spectrum

• Radio waves
• Infrared rays
• Visible light
• Ultraviolet rays
• X-rays
• Gamma rays

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Radio Waves

• AM (frequency is the same and amplitude changes)
• FM (frequency changes and amplitude is the same)

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Which is AM radio?
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Television Waves

• Same as radio but also sends pictures.

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Microwaves

• Waves of this frequency are absorbed by water and
  heat food.
• Food is in motion and therefore creates heat

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How is a cell phone like a microwave?
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Get off the phone!
10950 watts is the same as 1.09 kWatts
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Now tell me how a cell phone is like a microwave!!

• If you talk on cellular phone more than 20 min.
  your brain temperature raises for up to 2
  degrees.

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Low wavelength, frequency energy
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Infrared Rays

• Used as a source of heat
• Discover areas of heat differences
• Cant see but skin can sense.

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A thermogram can be used to diagnose problems in
a utility line.
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More Thermograms

• What color is showing cooler temperatures?

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Visible Light

• The only part of the spectrum the human eye can
  see.
• Each color of light corresponds to a different
  range of wavelengths.

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How to remember order

• Red part of visible light it towards Infrared
• Violet part of visible light is towards
  ultraviolet

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Ultraviolet Rays

• Uses in health and medicine, and in agriculture.
• helps your skin produce vitamin D
• used to kill microorganisms
• Treats jaundice in newborn
• help plants grow.
• Negative Can cause skin
• cancer and blindness in
• humans

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X-rays

• Used in medicine, industry, and transportation to
  make pictures of the inside of solid objects.

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I can see that!
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Gamma Rays

• Used in the medical field and in industrial
  situations as an inspection tool.
• used to make pictures of the human brain
• used in radiation therapy to kill cancer cells
• used to check pipes by taking pictures to look
  for rusting, cracks, or other signs of damage.

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Electromagnetic Spectrum You will make a chart
similar to this but far more detailed.
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Keep in mind

• The electromagnetic spectrum can be expressed in
  terms of energy, wavelength, or frequency.
• Frequency is measured in cycles per second (which
  is called a Hertz)
• Wavelength is measured in meters
• Energy is measured in electron volts.

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Lets compare them.
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18.3 Behavior of Light
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How does light do that?

• When light strikes a new medium, the light can be
  
• Reflected
• Absorbed
• Transmitted.

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Reflection

• Regular light waves hit a smooth surface

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Reflection

• Diffuse light waves hit a rough surface and
  reflects light in many different directions.

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Regular (same as Specular)
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How does light do that?

• When light is transmitted, it can be
• Refracted
• Polarized
• Scattered.

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Refraction

• Light refracts (or bends) when it moves from one
  medium to another.
• What are the 2 mediums shown here?

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Polarization

• A vertical polarizing filter blocks light that is
  horizontally polarized.

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Polarization

• A horizontal polarizing filter blocks light that
  is vertically polarized.

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Polarization

• Put them together and almost ALL light is blocked
  out.
• View Clip

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Scattering

• Light is redirected as it goes thru a medium.
• Blue, green, and yellow wavelengths of sunlight
  are heavily scattered in certain weather
  conditions.
• What color is left?

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The Color of the Sun
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The science behind it

• Description at sunrise and sunset the sun is
  yellow, orange or red
• Physical process Rayleigh scattering by air
  molecules and fine dust particles.
• Explanation on clear days only the blue light is
  scattered away, on hazy days the yellow and the
  orange wavelengths are also scattered and only
  the red remains in the direct solar light.
• Conclusion Red sunsets suggest that there is
  dust in the air (pollution, haze over the ocean,
  volcanic activity, dust storms).

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The Timing of the Sunset Sunrise
We see the sun before it actually rises above the
horizon and after it sets below the horizon.
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Twilight
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Flattening of the Suns Disk at Sunset
Green flash
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Green Flash?

• Your thinking, Ms. Lolich first the Hulk and now
  this?

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Green Flash

• They are usually seen at an unobstructed horizon,
  such a
• Higher frequency light (green/blue) curves more
  than lower frequency light (red/orange), so
  green/blue rays from the upper limb of the
  setting sun remain visible after the red rays are
  obstructed by the curvature of the earths over
  the ocean.

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Development of Green Flash
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A larger than usual green flash in Santa Cruz
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Stages of a green flash
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Quiz Regular or Diffuse?
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As the wavelength decreases from the red end of
the spectrum to the violet end, what happens to
the frequency?

• It remains constant.
• It increases.
• It decreases.
• It is impossible to predict what will happen.

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As the wavelength decreases from the red end of
the spectrum to the violet end, what happens to
the frequency?

• It remains constant.
• It increases.
• It decreases.
• It is impossible to predict what will happen.

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The End