A light review: Our primary source of light is the sun. Light travels in straight lines at a speed of 3.00 x 108 m/s. Light energy from the sun travels through space , reaches earth, and some of it turns to heat energy and warms the earth’s air. Light from the sun also travels to the cells of green plants (producers) and is stored as energy. The peak wavelength of our sun is green. When light reaches an object, it is absorbed/ reflected (giving it colour), or passes through it.

EM Theory Henry and Faraday linked electricity and magnetism by finding that changing magnetic fields will generate a current in nearby conductors. The linking of these two forces (electric and magnetic) allowed physicists to move closer to the ultimate goal of linking all the forces into a Grand Unified Theory (G.U.T.) The nuclear forces (weak and strong) are explained by an interaction of EM waves Gravity is the elusive force that has not been nailed down into the G.U.T.

EM Theory In 1846, Faraday theorized that light could be a vibration of electric and magnetic fields (dropping the ether model) James Maxwell proved Faraday’s theory mathematically, 10 years later. All electromagnetic waves are generated by accelerated charges. As a charge is accelerated, it will continually emit excess energy as an EM wave (to limit the particle’s velocity to less than “c”). The accelerated charge generates a changing magnetic field which creates a changing electric field, which generates a changing magnetic field, etc

EM Theory

What is light really? Electromagnetic radiation waves Light waves are three dimensional Light waves vibrate in all planes around a center line. The waves have high points called “crests.” Waves also have low points called “troughs.” *The distance from one crest to the next crest is called a “wavelength.” *The number of waves passing a given point in one second is called the “frequency.” wavelength

*Electromagnetic Radiation Electromagnetic radiation can be described in terms of a stream of photons. Each photon is traveling in a wave-like pattern, moving at the speed of light and carrying some amount of energy. The only difference amongst radio waves, visible light, and gamma-rays is the amount of energy of the photons. Radio and AC waves have photons with low energies. Microwaves have a little more energy than radio waves. Infrared has still more energy. As we move down the chart we see visible, ultraviolet, X-rays, and gamma-rays whose photon energies gradually increase. Gamma and Cosmic rays have the highest energy waves.

Remember radio waves are long…and gamma rays are small. Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic

EM Theory An electron forced to oscillate at 102.1 MHz will produce an FM radio wave An electron accelerated by a Mega-Volt and fired into a metal target will produce X-rays (rapid deceleration of electrons) A magnetron in a microwave oven accelerates charges to produce an EM wave that is forced to oscillate at about 2.4 x 109 Hz (the electric field spins polar water molecules to create heat).

Radio (Longest electromagnetic waves) Emitted by Astronomical Objects Radio Station Transmitters Detected by Ground based radio telescopes *If you turn on a radio,, it will convert the radio wave energy into sound energy.

Television Shorter than radio, also used to carry messages (pictures & sound) to our TV sets. We can detect the TV waves around us with our televisions.

Microwave Emitted by: Detected by Gas clouds collapsing into stars Microwave Ovens Radar Stations Cell Phones Detected by Microwave Telescopes Food (heated) Cell phones Radar (systems)

Infrared (Heat or Thermal) Are you a source of infrared? YES you are! Emitted by Sun and stars (Near) TV Remote Controls Food Warming Lights (Thermal) *Everything at room temperature or above,=HEAT Detected by Infrared Cameras TVs, VCRs, Your skin

Visible Each color is a different size wave Visible Each color is a different size wave. Red the longest & violet the shortest Emitted by The sun and other astronomical objects Laser pointers Light bulbs Detected by Cameras (film or digital) Human eyes Plants (red light) Telescopes RoyG.Biv

Ultraviolet Sunburn / black light He can get skin cancer! Emitted by Tanning booths (A) The sun (A) Black light bulbs (B) UV lamps Detected by Space based UV detectors UV Cameras Flying insects (flies)

X-ray Emitted by Detected by Astronomical objects X-ray machines CAT scan machines Older televisions Radioactive minerals Airport luggage scanners Detected by Space based X-ray detectors X-ray film CCD detectors

Chandra X-ray Observatory Chandra is designed to observe X-rays from high energy regions of the universe, such as the remnants of exploded stars. The most sophisticated observatory built to date. Deployed by the Space Shuttle Columbia on July 23, 1999, Chandra X-ray Observatory *Slide from 2004 NSTA Conference

Gamma Ray (Short electromagnetic waves but more energetic) Emitted by Radioactive materials Exploding nuclear weapons Gamma-ray bursts Solar flares Detected by --Geiger counters Gamma detectors and astronomical satellites Medical imaging detectors

Sources of g-ray Emission • Black holes • Active Galaxies • Pulsars • Diffuse emission • Supernovae Gamma-ray bursts • Unidentified

COSMIC Rays (The highest energy waves and the deadliest) Cosmic rays come from deep space and can pass through the Earth. Neutrinos are emitted by all stars Dark matter/energy?

How big are the waves? A great question! Radio waves= (Buildings to human size); Microwaves (Humans-beetles); Infrared waves (Eye of a needle); Visible waves (microscopic size)! All the rest are the size of molecules, atoms, atomic nuclei and smaller..

EM Waves In 1865, Maxwell proved that all EMR travels at the speed of light where: The permittivity of free space is εo = 8.85x10-12 C2/(N●m2) and the permeability of free space is μo = 4π x 10-7 T●m/A The speed of light is defined today as c = 299 792 458 m/s

EM Waves EM waves are produced using the following steps: Energy is supplied to a source of EM radiation The source does work on charges making them accelerate The charges continually emit EMR radiating away excess kinetic energy The atomic model proved a challenge as accelerated electrons (in the Bohr-orbit model) did not radiate EMR continuously (the atom would collapse) and Bohr solved this by stating this didn’t occur in the atom.