A light review Our primary source of light

A light review: • Our primary source of light is the sun. • Light travels in straight lines at a speed of 186, 000 miles per second. • Light waves travel faster than sound waves. • 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. • When light reaches an object, it is absorbed, reflected, or passes through it.

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

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: – 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

Let’s take a look at Herschel’s Experiment • Herschel’s Experiment – Discovered Invisible Light – In 1800, Herschel placed his control thermometer just outside the red end of the spectrum – Result: The outside thermometer registered the highest temperature

Let’s set up Herschel’s Experiment • Set up of Box Design for Conducting the Herschel Experiment.

Conducting Hershel’s Experiment • • Place a sheet of white paper inside a cardboard box Tape three thermometers together and place inside box Cut a small notch in the top of the box and position a glass prism so that the spectrum is projected inside the box Arrange thermometers so that one is just outside the red end of the spectrum, with no visible light falling on it

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

Ultraviolet Sunburn / black light • 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)

• Emitted by – – – X-ray 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 *Slide from 2004 NSTA Conference • 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,

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?

• 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, atomic nuclei and smaller. .