Light

Light & Light & ElectromagnElectromagnetic waves etic waves

Jitesh Aggarwal Jitesh Aggarwal XII Science (2011-12)XII Science (2011-12)FAITH ACADEMYFAITH ACADEMY

A light review:• Our primary source of light is the sun.• Light travels in straight lines at a speed of

186,000miles 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.

Sensing Light

• Humans have two light detectors.

• Do you know what they are called?

Did you realize cameras and camcorders are light detectors too?

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 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 sense 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

places 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 the thermometers so that one is just outside the red end of the spectrum, with no visible light falling on it

VisibleEach 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

Prism Power: Roy G. Biv Activity

• *What happens when light shines through prisms?

• Materials :prism, PASCO “wave it,”equipment, paper, +7 Roy G. Biv crayon colors,

• 1. Give handouts. Darken the room and turn on light source. What color is the light? If I use a prism can you predict what will happen to the light?

• 2.Now use the prism. What color is the light?• 3. Color in your hand out to match the spectrum.

*PASCO Probe Activity OR *AIMS:Primarily Physics: Prism Power Activity

UltravioletSunburn / 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)

X-ray• Emitted 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

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.

• A great question!• Radio waves= (Buildings to human size);• Microwaves

(Humans-beetles);• Infrared waves (Eye of a needle);Visible waves (microscopic size)!

WOW! All the rest are the size of molecules, atoms, atomic nuclei and smaller..