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Waves All Around: the Electromagnetic Spectrum in Everyday Life

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Waves All Around: the Electromagnetic Spectrum in Everyday Life Waves All Around: the Electromagnetic Spectrum in Everyday Life Karl Scheidt Department of Chemistry Great Minds, Great Ideas Series Finale Part I Overview • Introduction to the electromagnetic spectrum (waves? what waves?) • Basics, background and history • EM spectrum in our lives • Societal impact & questions • Discussion/Conclusion Disclaimer: I am not a physicist or electrical engineer! all rights reserved Questions.... • How much of the EM spectrum can we see? • Who discovered this stuff? • Why should I care? • Where is the EM spectrum and who “owns” it? • What does the Titanic have to do with the EM spectrum? • What does“radiation” do to cancer? all rights reserved April 14, 1912 • Maiden voyage of RMS Titanic • Received ice warnings (how??) that were discounted. • Hits iceberg at 11:40 PM...sinks by 2:30 AM. • Sends “C.Q.D.” signal 6x (how?)- Marconi’s earlier version of S.O.S. Then switches to S.O.S. by 12:45 AM. • Olympic (500 mi away), Baltic and Carpathia and others rush to coordinates- ~800 saved. • EM spectrum critical to long distance communication. How did this come about? http://www.hf.ro/#trd all rights reserved The only known photograph of Titanic's Marconi room Olympic's Marconi Room 25 year old 21 year old John (Jack) G. Phillips Harold Bride died on Titanic, not recovered survived all rights reserved Guglielmo Marconi • G. Marconi invents the radio telegraph ~1895 (20 yrs old). • awarded the 1909 Nobel Prize in Physics • Father of wireless communication. • RMS Titanic “wireless operators” (J. Phillips and H. Bride) employed by Marconi Comm. Co., not White Star Line. • “Those who have been saved, have been saved through one man, Mr. Marconi...and his marvelous invention,” British Postmaster General during Court of Inquiry, 1913. • The closing of one chapter and beginning of another in human technology. all rights reserved Introduction: Basics • Wavelength (λ) and frequency • The wave/frequency equation: where c = speed of light • higher frequency = smaller wavelength • lower frequency = longer wavelength all rights reserved Introduction: Basics • The EM spectrum is composed of waves • These waves have energy. • Similar to sound waves, but different: • Have 2 components: magnetic & electrical all rights reserved More Basics today’s lecture http://mynasadata.larc.nasa.gov/science-processes/electromagnetic-diagram/ all rights reserved How much can we see? If the entire electromagnetic spectrum stretched for 3,000 miles from Los Angeles to New York, our eyes only detect an amount equal to the length of one of our arms (the visible spectrum). All the rest of it (99.99999%) is lost from our everyday awareness. all rights reserved Key Players • James Clerk Maxwell (E and M are connected) • Max Planck (black body radiation) • Albert Einstein (photoelectric effect) • G. Marconi (“father of radio”) • Wilhelm Rontgen (discoverer of X-rays) • Philo Farnsworth/David Sarnoff (television) • Many others... all rights reserved James C. Maxwell • Formulated equations that describe electricity, magnetism and optics as “manifestations of the same phenomenon”, i.e., the electromagnetic field. • One of the great discoveries/developments in all of science. • In 1865, he demonstrated that electric and magnetic fields travel through spaces as waves at the speed of light. • Proposed (correctly) that light is composed of both E & M fields. • On par with Newton and Einstein in terms of scientific impact. Laid the ground work for all EM discoveries/devices. all rights reserved Maxwell’s Insight Maxwell-Faraday eq. (law of induction) E = electric field, B is magnetic field: a time-varying magnetic field is always accompanied by a spatially-varying electric field, and vice-versa • Maxwell-Faraday equation: Varying a magnetic field creates (induces) an electric field. The basis of all electric motors. all rights reserved Electric Motors • Thanks to Faraday and Maxwell, we can interconvert magnetic and electric fields! • Motors: Applied electric fields can rotate a shaft in a magnetic field (motors). • Power: Turbines (turned by water, steam or wind) create magnetic field disturbance that generates electric field. all rights reserved Max Planck • Theoretical physicists (Nobel Prize in 1918) • Father of quantum theory • Started working on “black body radiation” by commission from electric companies. • BBR: EM waves (radiation) emitted by source at constant temperature. • Created equation that fit the experimental data of BBR by assuming the energy was “quantized”. Radical notion! • Frequency is proportional to temperature The temperature of a Pāhoehoe lava flow can be estimated by observing its color. The result agrees well with measured temperatures of lava flows at about 1,000 to 1,200 °C (1,832 to 2,192 °F all rights reserved Albert Einstein • Discovered the photoelectric effect (1905) for which he received the Nobel Prize in physics (1921). • Needed to invoke “quantization” of EM radiation to explain this phenomenon. Inspired by Planck. • Energy of the photons = energy of electrons ejected. Electrons are in specific energy states. • Basis of solar energy: light = electric current all rights reserved 20th Century Life • “Wireless” (AM then FM radio) • Radar • Television • Cell phones & WiFi • Microwave ovens • MRI (magnetic resonance imaging) • X-rays & Gamma knives...(?) all rights reserved Radio • Information, such as sound, is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude, frequency, phase, or pulse width. • Both Edison and Tesla were in fierce competition in late 1890’s for wireless transmission of energy (radio waves). • Marconi the first to successfully build system of transmitting signals for long distance. (1905) • The overall process: all rights reserved Radio • Wavelength = 1 mm to 1 km. Freq. 300 GHz-3Hz. Very little energy. • AM (amplification modification) developed first. Then FM (frequency modulation). • FM stations now predominate normal radio listening. AM signals have much more range (>1000 miles). all rights reserved Radio Spectrum all rights reserved Radar • Radar: RAdio Detection And Ranging • 1886: German physicist H. Hertz demonstrates that radio waves are reflected by solid objects. • US Navy investigates in the early 1900s... RADAR is born. Major world wide conflict necessary to prompt development. all rights reserved Battle of Britain • Summer/Fall of 1940- Germans initiate major aerial attack/bombing campaign to invade & defeat England. • Surprise attacks early on were devastating. A NEW tool was necessary to save lives and England. • “Chain Home” radar defenses were established for early warning of Luftwaffe attacks. • A. Loomis and Tuxedo Park lab was instrumental in making key radar advances (range, precision) which saved England and possibly WWII. all rights reserved Battle of Britain Suggested Reading: TUXEDO PARK: A Wall Street Tycoon and the Secret Palace of Science That Changed the Course of World War II all rights reserved Weather Tracking • During World War II, military radar operators noticed noise in returned echoes due to rain, snow • Radar is major advance in weather tracking and forecasting. Now critical in tornado and hurricane predictions. • Doppler radar provides information about MOVEMENT of targets as well as position (change in frequency). all rights reserved Doppler Effect • The change in frequency of wave for an observer relative to a MOVING source (sirens, trains). • Can be sound waves, radio waves (RADAR), etc. not moving < speed of sound > speed of sound all rights reserved Television • Radio wave transmissions in 54-890 MHz frequency band. (VHF & UHF) Now all digital signals & HD. HD means more information sent per “cycle”- more pixels. • First public demonstration in Berlin in 1931- 1936 Olympic games were broadcast live in Berlin to public. • Philo Farnsworth (1906-1971) was major TV pioneer- inventor of electric television. He battled RCA (and David Sarnoff) for patent priority and technology for decades. • “Cable” now major player vs. over the air (OTA). • Satellite TV use 950-2150 MHz frequencies. Satellites are in geostationary orbits (~23,000 mi above equator). all rights reserved Television Suggested Reading: The Last Lone Inventor: A Tale of Genius, Deceit, and the Birth of Television Evan Schwartz “The fascinating inside story of how this eccentric loner invented television and fought corporate America." —Walter Isaacson, biographer, past chariman of CNN all rights reserved Satellite Bands- wow! all rights reserved Break! all rights reserved Cell Phones • In WWII, military used hand-held radio transceivers. • 1960s-70s: Frequency “reuse” and switching of call (handoff) from one tower to multiple receivers developed. “Cell” is a land area covered by a transceiver (base station). • April 1973, Martin Cooper of Motorola makes 1st mobile telephone call (to J. Engel at Bell Labs). 1 kg with 10 h charge for 30 min (analog signal, 1G). • 4G systems now all digital and avoids circuit switching. • Has clearly changed how the world communicates (Facebook, Twitter, etc). How is all this information handled??? all rights reserved Cell Phones • CDMA: Code division multiple access. • Each call gets a unique “code” • Information is spread over all available frequencies. “Multiple” means that >1 user can use the same frequency. • CDMA greatly increases practical “bandwidth”, range of frequencies available to transmit specific information. • Operates in the 800 MHz and 1900 MHz bands. • Europe uses GSM (Global System for Mobile comm) protocol. Uses
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