Presentation on theme: "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."— Presentation transcript:
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 Spectrum Increasing 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 Lets 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