Post on 16-Dec-2015
transcript
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
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
X-rays and Gamma Rays• Black holes• Active Galaxies• Pulsars• Supernovae• Gamma-ray bursts• Unidentified
• 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 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.