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An Introduction to Light
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
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.”
wavelength
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!
Heinrich Hertz
• German Physicist• In 1887, he proved
what Maxwell had predicted 23 years earlier
• Guess who got credit for the work?
• Good beard…at best
The Electromagnetic Spectrum
Notice the wavelength is long(Radio waves) and gets shorter (Gamma Rays)
Electromagnetic SpectrumIncreasing Energy
Radio waves
• Lowest energy Electromagnetic (EM) waves
Microwaves
• Next highest energy EM waves
• Used in telecommunications, microwave ovens and astronomy (measuring background radiation from Big Bang Theory)
Infrared Light
• Used in remote controls, lasers, heat detection, physical therapy and food warming
Visible light
• Only portion of the spectrum that can be seen
• Examples: human vision, rainbows, visible lasers
Activity
• Let’s stop there and have a look at an experiment first done by Sir Isaac Newton in the year 1666
Ultraviolet light• Invisible• Causes skin to tan
and burn• Kills bacteria in food
and water• “black” lights
X-rays
• Very high energy EM waves
• Short wavelength• Used in medical
imaging, security equipment and cancer treatment
Gamma rays
• Highest energy EM waves
• Used in cancer treatment
• Product of some nuclear decay
• Incredible Hulk???
How is light produced?
I mean besides from the Sun…
Light from Incandescence
• Producing light as a result of high temperature
• Eg. Stove burner on high, light bulb, molten glass, sparks, etc.
Light from Electric Discharge
• Producing light as a result of an electric current running through a gas
• Eg. Lightning, neon lights, etc.
Light from Phosphorescence
• “glow-in-the-dark” objects are coated with phosphors (material that gives off light)
• Eg. Toys, watch dials, etc.
Light from Fluorescence
• When an object absorbs UV light and immediately releases the energy as visible light
• Can laundry soaps really make clothes brighter?
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.
• When chemi-luminescence occurs in nature
• Quite common!• Eg. Bacteria,
fungi, fish, and of course glow-worms and fireflies
Light from Bioluminescence
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
Triboluminescence
• Production of light when certain crystals are scratched, crushed or rubbed together
• Has no real use at this time
Activity
• Try Triboluminescence