Light Waves

Light Waves• Electromagnetic waves that radiate• Made of small pieces or particles of “light”

energy called photons• The more particles you put in front of a

light wave the SLOWER it travels!• Transparent-Light passes through it & you

can see through it• Translucent- Light passes through it but

you can’t see through it• Opaque- Light does not pass through it &

you can’t see through it

More than meets the eye!

Electromagnetic Spectrum

• The full range of frequencies, from radio waves to gamma rays, that characterizes light

• The electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency. Each way of thinking about the EM spectrum is related to the others in a precise mathematical way.

• The wavelength equals the speed of light divided by the frequency

Light Review

• White Light = the presence of all colored light (all wavelengths of light are being reflected)

• Black = the absence of all colored light (all wavelengths of light are being absorbed)

• Why do things appear the color that they do?

• Wavelength-Difference between a point on one wave and the same point on the next cycle of the wave

• Unit-Meters – More commonly in nanometers (1 nm = 10-9

meters)

• Frequency-The number of wave cycles passing a point at a given time.

Wavelength and Frequency

Wavelength and Frequency

• For any kind of wave there exists a simple relationship between wavelength and frequency.

• The wavelength is measured as the distance between two successive crests in a wave. The frequency is the number of wave crests that pass a a given point in space each second.

Light Waves

• In a light wave if you change the frequency of the wave you change the color

• Remember changing frequency changes wavelength

• Each color in the visible spectrum has its own wavelength range!

Light Waves

• In a light wave if you change the amplitude of the wave you change the brightness

• The greater the amplitude the brighter the light wave!

Radio(Lowest Frequency & Longest Wavelength)

• Emitted by– Astronomical Objects– Radio Station

transmitters

• Detected by– Ground based radio

telescopes– Radios

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(Near and Thermal)

• Emitted by– Sun and stars (Near)– TV Remote Controls– Food Warming Lights

(Thermal)– Everything at room

temp or above

• Detected by– Infrared Cameras– TVs, VCRs,– Your skin

Visible

• Emitted by– The sun and other

astronomical objects– Laser pointers– Light bulbs

• Detected by– Cameras (film or

digital)– Human eyes– Plants (red light)– Telescopes

The Visible SpectrumThe Visible Spectrum

•A range of light waves extending in wavelength from about 400 to 700 nanometers (nm).

Highest FrequencyShortest Wavelength

Lowest FrequencyLongest Wavelength

Ultraviolet

• 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

Gamma Ray

• Emitted by– Radioactive materials– Exploding nuclear

weapons– Gamma-ray bursts– Solar flares

• Detected by– Gamma detectors and

astronomical satellites– Medical imaging detectors

Highest Frequency & Shortest Wavelength

Skip the Following Slides

X-rays and Gamma Rays• Black holes• Active Galaxies• Pulsars• Supernovae• Gamma-ray bursts• Unidentified

Examples from Space

• The distance from one wave crest to the next

• Radio waves have longest wavelength and Gamma rays have shortest!

Wavelength

Electromagnetic Waves

• Transverse waves consisting of changing electric fields and changing magnetic fields– Produced by constant changing fields– Can travel through a vacuum and or empty

space as well as through matter– Electromagnetic Radiation

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

Conducting 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

Red Sky – Blue Sky

• A demonstration used to illustrate how the gases in the atmosphere scatter some wavelengths of visible light more than others.

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