Transcript EM Spectrum
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 Notice from the definitions we can relate the properties of a wave to one another frequency 1 period wavelength velocity 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 1 1Hz s 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 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 waves Produced 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 Duality Light can behave like a wave or like a particle A “particle” of light is called a photon Radio waves Longest wavelength EM waves Uses: TV broadcasting AM and FM broadcast radio Avalanche beacons Heart rate monitors Cell phone communication Microwaves Wavelengths from 1 mm- 1 m Uses: Microwave ovens Bluetooth headsets Broadband Wireless Internet Radar GPS Infrared Radiation Wavelengths in between microwaves and visible light Uses: Night vision goggles Remote controls Heat-seeking missiles Visible light Only 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 Ultraviolet Shorter light Uses: wavelengths than visible 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-rays Tiny wavelength, high energy waves Uses: Medical imaging Airport security Inspecting industrial welds Gamma Rays Smallest 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 ( ~60,00 The Sun at Different Wavelengths Visible X-ray Ultraviolet 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 Credits J. 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