Properties of Light

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Chapter 26

• Properties of Light

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Electromagnetic Radiation
Light
Photons
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These three are the same

• Light
• pure energy
• Electromagnetic Waves
• energy-carrying waves emitted by vibrating
  electrons
• Photons
• particles of light

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Electromagnetic Wave Velocity

• The speed of light is the same for all seven
  forms of light.
• It is 300,000,000 meters per second or 186,000
  miles per second.

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The Electromagnetic Spectrum

• Radio Waves - communication
• Microwaves - used to cook
• Infrared - heat waves
• Visible Light - detected by your eyes
• Ultraviolet - causes sunburns
• X-rays - penetrates tissue
• Gamma Rays - most energetic

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THE ELECTROMAGNETIC SPECTRUM

• Sources

• EM Waves

Radio Waves
Vibrating charges
Molecular vibrations
Microwaves
Infrared
Molecular vibrations
Visible
Atomic vibrations
Ultraviolet
Atomic vibrations
Atomic vibrations
X-rays
Gamma rays
Nuclear vibrations
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The Electromagnetic Spectrum

• A range of light waves extending in wavelength
  from radio waves to gamma rays

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• The Visible Spectrum
• A range of light waves extending in wavelength
  from about 400 to 700 namometers.

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Transparent Materials

• Transparent - the term applied to materials
  through which light can pass in straight lines

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Opaque Materials

• Opaque - the term applied to materials that
  absorb light

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Example Questions

• Are clouds transparent or opaque to visible
  light?
• Answer opaque
• Are clouds transparent or opaque to ultraviolet
  light?
• Answer transparent

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Shadows

• Umbra - the darker part of a shadow where all the
  light is blocked
• Penumbra - a partial shadow
• These terms also apply to Solar Eclipses and
  Lunar Eclipses.

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Solar Eclipse
Umbra
Sun
Full Shadow
Earth
Moon
Partial Shadow
Penumbra

• A solar eclipse occurs when the Moon passes in
  front of the Sun.

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Annular Eclipse
Again looking at the sun while the moon passes
in front of it.
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Lunar Eclipse
Sun
Earth
Moon

• A lunar eclipse occurs when the Moon passes into
  the Earth's shadow.

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Questions

• Which type of eclipse is dangerous to view with
  the unprotected eye?
• Why are lunar eclipses more commonly seen than
  solar eclipses?

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SEEING LIGHT - THE EYE

• Cornea -

does most of the focusing

• Iris -

has the eye color and controls light intensity

• Pupil -

the hole in the

• Lens -

does remainder of focusing

• Retina -

location of light sensors, has rods and cones
center of vision, predominantly cones

• Fovea -

• Blind spot -

optic nerve exit, no light sensors
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Color Deficiency
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Myopia (Near-Sightedness)
People with near-sightedness cannot see clearly
at distance.
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Hyperopia (Farsightedness)
People with far-sightedness cannot see clearly up
close.
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Chapter 26 Review Questions
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Chapter Review

• RQ 7,9,11,16,17,21,24,26
• EX 7,11,13,17,29,31,35,38,39,41

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You will observe a total eclipse of the sun
when...
(a) you stand in the penumbra of the moons
shadow (b) you stand in the umbra of the moons
shadow (c) sunlight diffracts around the
moon (d) sunlight reflects from the moon to the
earth
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The speed of light...

• (a) has never been measured
• (b) is about the same as that of sound
• (c) is infinitely fast
• (d) is very fast, but not infinite

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In the dark at late evening, no color is seen
because of lack of stimulation of

• a. rods.
• b. cones.
• c. cornea.
• d. crystalline lens.

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End of Chapter 26