electromagnetic radiation
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Electromagnetic Radiation. Physics Relax and Enjoy the Ride… It’s quite a ride. Waves… a review. Most waves are either longitudinal or transverse. Sound waves are longitudinal. But all electromagnetic waves are transverse…. ?. ?. Wave Relationships. - PowerPoint PPT PresentationTRANSCRIPT
Electromagnetic Radiation
Physics
Relax and Enjoy the Ride… It’s quite a ride.
Waves… a reviewMost waves are either longitudinal or transverse.
Sound waves are longitudinal.
But all electromagnetic waves are transverse…
?
?
Wave Relationships
Notice from the definitions we can relate the properties of a wave to one another
periodfrequency 1
wavelengthvelocity wavelength frequency
period
Wave Relationships Frequency is usually expressed in the unit of Hertz
This unit is named after a German scientist who studied radio waves
For example, if a wave has a period of 10 seconds, the frequency of the wave would be 1/10 Hz, or 0.1 Hz
sHz
11
Note that light is always traveling at the same speed
(c ~ 3 x 108 m/s)
Remember: velocity = wavelength x frequency
If frequency increases, wavelength decreases If frequency decreases, wavelength increases
Electromagnetic wavesProduced by the movement of electrically charged particles
Can travel in a “vacuum” (they do NOT need a medium
Travel at the speed of light
Also known as EM waves
Wave-particle DualityLight can behave like a wave or like a particle
A “particle” of light is called a photon
Radio wavesLongest wavelength EM wavesUses:
TV broadcasting AM and FM broadcast radio Avalanche beacons Heart rate monitors Cell phone communication
MicrowavesWavelengths from 1 mm- 1 mUses:
Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS
Infrared RadiationWavelengths in between microwaves and visible light
Uses: Night vision goggles Remote controls Heat-seeking missiles
Visible lightOnly type of EM wave able to be detected by the human eye
Violet is the highest frequency light
Red light is the lowest frequency light
Wavelengths of Light - Visible
What we see as white light is actually made up of a continuum of components
Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)
There is actually a continuous transition of color, each with its own wavelength and frequency
UltravioletShorter wavelengths than visible light
Uses: Black lights Sterilizing medical equipment Water disinfection Security images on money
Ultraviolet (cont.)UVA UVB and UVC
Energy Highest of UV waves
Lower than UVA
Health risks
Extremely low risk for DNA damage Can destroy Vitamin A in skin
Can cause DNA damage, leading to skin cancer Responsible for sunburn
X-raysTiny wavelength, high energy waves
Uses: Medical imaging Airport security Inspecting industrial welds
Gamma RaysSmallest wavelengths, highest energy EM waves
Uses Food irradiation Cancer treatment Treating wood flooring
Blackbody Radiation
Cool gas ( ~60K)
Young star ( ~600K)
The Sun (~6000K)
Hot stars in a cluster ( ~60,000K)
The Sun at Different Wavelengths
Visible Ultraviolet
X-ray X-ray
With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The CMB's serendipitous discovery in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned them the 1978 Nobel Prize.
Doppler Effect
The motion of an object can be measured through a change in the frequency of the waves emitted by the object
The increase in pitch of an approaching police car is caused by the compression of the sound wave The pitch decreases as the police car moves away
Doppler Shift
In astronomy, the same effect happens to light waves
A source that is moving away will appear redder (redshift)
A source that is moving toward us will appear bluer (blueshift)
Note: Only objects moving toward or away from us (radial motion) will show this effect
EM Spectrum HW:p. 389 # 1-3, 31-35
Powerpoint CreditsJ. Beauchemin 2009 free online ppt
Image credits1. http://www.antonine-education.co.uk/New_items/MUS/imag
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Image Credits13. http://farm3.static.flickr.com/2385/2381723771_1
2548f4bd1.jpg?v=121742987914. http://intamod.com.au/images/uv2.JPG15. http://science.hq.nasa.gov/kids/imagers/ems/
xrays.html16. http://www.sciencelearn.org.nz/var/
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