An Introduction to Light

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An Introduction to Light
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What is light?

• Sun is our closest star
• Source of all energy on Earth
• Energy produced by nuclear reactions in core
  reach Earth in form of light (and heat)
• Source of all life on Earth

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What is light really?Electromagnetic radiation
waves

• Light waves are three dimensional.
• Light waves vibrate in all planes around a center
  line.
• Waves have high points called crests.
• Waves also have low points called troughs.
• Distance from one crest to the next crest is
  called a wavelength.
• Number of waves passing a given point in one
  second is called the frequency.

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James Clerk Maxwell

• English Physicist
• In 1864, predicted that electricity forms a
  change travelling through space (electromagnetic
  waves)
• Also knew that it would travel at the speed of
  light
• Great beard!

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Heinrich Hertz

• German Physicist
• In 1887, he proved what Maxwell had predicted 23
  years earlier
• Guess who got credit for the work?
• Good beardat best

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The Electromagnetic Spectrum
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Notice the wavelength is long(Radio waves) and
gets shorter (Gamma Rays)
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Electromagnetic Spectrum
Increasing Energy
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Radio waves

• Lowest energy Electromagnetic (EM) waves

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Microwaves

• Next highest energy EM waves
• Used in telecommunications, microwave ovens and
  astronomy (measuring background radiation from
  Big Bang Theory)

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Infrared Light

• Used in remote controls, lasers, heat detection,
  physical therapy and food warming

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Visible light

• Only portion of the spectrum that can be seen
• Examples human vision, rainbows, visible lasers

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Activity

• Lets stop there and have a look at an experiment
  first done by Sir Isaac Newton in the year 1666

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Ultraviolet light

• Invisible
• Causes skin to tan and burn
• Kills bacteria in food and water
• black lights

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X-rays

• Very high energy EM waves
• Short wavelength
• Used in medical imaging, security equipment and
  cancer treatment

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Gamma rays

• Highest energy EM waves
• Used in cancer treatment
• Product of some nuclear decay
• Incredible Hulk???

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How is light produced?

• I mean besides from the Sun

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Light from Incandescence

• Producing light as a result of high temperature
• Eg. Stove burner on high, light bulb, molten
  glass, sparks, etc.

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Light from Electric Discharge

• Producing light as a result of an electric
  current running through a gas
• Eg. Lightning, neon lights, etc.

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Light from Phosphorescence

• glow-in-the-dark objects are coated with
  phosphors (material that gives off light)
• Eg. Toys, watch dials, etc.

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Light from Fluorescence

• When an object absorbs UV light and immediately
  releases the energy as visible light
• Can laundry soaps really make clothes brighter?

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Light from Chemiluminescence

• Production of light as a direct by-product of a
  chemical reaction
• Almost no heat produced, called cold light
• Eg. Glow sticks, Luminol (CSI), etc.

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Light from Bioluminescence

• When chemi-luminescence occurs in nature
• Quite common!
• Eg. Bacteria, fungi, fish, and of course
  glow-worms and fireflies

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Light from a Light-Emitting Diode

• Aka LED light
• Electronic device allows electricity to flow in
  one direction
• With current, LED emits light
• Cooler and more energy efficient than incandescent

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Triboluminescence

• Production of light when certain crystals are
  scratched, crushed or rubbed together
• Has no real use at this time

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Activity

• Try Triboluminescence