The Lighter Side of Physics Prof. Roger McWilliams Department of Physics & Astronomy University of California, Irvine 92697, USA Email: email@example.com 949-824-6228 lab phone and fax The slides of this talk are posted at http://HAL9000.ps.uci.edu How did we get to today? • Civilization – the combination of culture and technology, both at relatively high levels. – Science and engineering create and make technology. – Science and engineering contribute to culture as well, but we shall focus on technology here. • Mechanical Age – previous societies were in ages described by mechanical names (stone, bronze, iron, steam) • Electrical Age – a new type of age The Electrical Age • Professors Maxwell & Faraday, and others, gave us the electrical age starting in about 1834. • From the following Maxwell’s Equations, we get modern civilization: Electricity, Magnetism, Electromagnetic Waves, Light come from understanding these equations (motors, power generators, lasers, transistors, et cetera). • To understand how important these equations are, try turning off your electrical power at home and work. • Maxwell’s Equations: D Free B 0 B E t D H jFree jFree jDisplacement t Michael Faraday Faraday’s Law: Time-changing magnetic fields make electric fields Result: Electric motors Generators Electric power plants for all electrical appliances and lights The Discovery of Electromagnetic Induction The experiment was conducted on 29 August 1831. When the primary circuit was closed, there was a displacement of the galvanometer needle in the secondary winding. Deflections of the galvanometer were only observed when the current in the electromagnet was switched on and off. This was the discovery of electromagnetic induction. Faraday’s notebook James Clerk Maxwell Scotland’s Greatest Physicist Celebrating the 175th Anniversary of Maxwell’s birth and the opening of the James Clerk Maxwell Laboratories at the Edinburgh Academy Albert Einstein (1931) “We may say that, before Maxwell, Physical Reality, in so far as it was to represent the process of nature, was thought of as consisting in material particles, whose variations consist only in movements governed by partial differential equations. Since Maxwell’s time, Physical Reality has been thought of as represented by continuous fields, governed by partial differential equations, and not capable of any mechanical interpretation. This change in the conception of Reality is the most profound and the most fruitful that physics has experienced since the time of Newton.” James Clerk Maxwell – A Commemorative Volume 1831-1931 Maxwell as a college student: Edinburgh University (1847-1850) Lecture courses attended Mathematics – Kelland Natural Philosophy – Forbes Logic – William Hamilton Publications in Transactions of the Royal Society of Edinburgh On the Theory of Rolling Curves The Equilibrium of Elastic Solids Books borrowed from library Cauchy: Calcul Différential Fourier: Théorie de la Chaleur Monge: Géometrie Desciptive Newton: Optics Poisson: Mechanics Taylor: Scientific Memoirs Willis: Principles of Mechanism Maxwell’s Equations Maxwell figured out how electromagnetic phenomena could be described by the mathematics in these four equations. Maxwell is responsible for dreaming up that last term in the last equation. • • • • Electric charges make electric fields Magnetic charges would make magnetic fields, but we’ve never seen any Time-changing magnetic fields make electric fields Electric currents or time-changing electric fields make magnetic fields D Free B 0 B E t D H jFree jFree jDisplacement t A Dynamical Theory of the Electromagnetic Field (1865) Maxwell's own view of this paper is revealed in what Francis Everitt calls “a rare moment of unveiled exuberance” in a letter to his cousin Charles Cay: “I have also a paper afloat, containing an electromagnetic theory of light, which, till I am convinced to the contrary, I hold to be great guns”. A Treatise on Electricity & Magnetism (1873) • “The most important aspect of any phenomenon from a mathematical point of view is that of a measurable quantity. I shall therefore consider electrical phenomena chiefly with a view to their measurement, describing the methods of measurement, and defining the standards on which they depend.” • “The internal relations of the different branches of the science which we have to study are more numerous and complex that those of any other science hitherto developed.” • “It appears to me, therefore, that the study of electromagnetism in all its extent has now become of the first importance as a means of promoting the progress of science.” And, once more, Maxwell’s Equations D Free B 0 B E t D H jFree jFree jDisplacement t Let’s see now, hmm, if that third equation says time-changing magnetic fields make electric fields, then the electric fields must be changing in time also (because we can start with zero magnetic field). And the fourth equation says time-changing electric fields make magnetic fields! Ah, ha! Does this mean that time-changing electric and magnetic fields can make each other with no other assistance? Can they go together through space on their own? Gee whillikers, you betcha! From National Radio Observatory http://www.nrao.edu/ The combination of time-changing electric and magnetic fields propagating through space or matter is what we call electromagnetic waves or light waves. Voodoo Science: A Trick with a ScientificSounding Premise False claim: This experiment shows how ESP makes successful predictions. Recent statistics suggest that this system can predict the correct outcome of your choice with 98% accuracy. Let me repeat. I am conducting an experiment. There are six small cards below. Select a card, stare at it, and be sure to remember it. By detecting your electromagnetic energy after your choice is made I can know your card. Prediction: I know your card and will now remove it from the cards. I have removed your card! Quantum consistency is: 671. This is not science. Even though scientific terms are used and there is a claim of predictive capability, there is no proof that your card was known via ESP sensing of electromagnetic energy. Instead, there only is proof that your card was removed. The trick is no cards shown above were on the previous page. But careful examination is needed to see that. Many people believe this trick actually shows ability to know the card you selected. Be skeptical of claims of predictive capability unless verified by scientists independent of those who would profit from claims. From Nasa Maxwell’s Colour Triangle Maxwell’s original version Modern version Light comes out of many plasmas. A solar flare, viewed through a blue filter, on our most important plasma, the Sun. Photo: NASA The Northern Lights (Aurora Borealis). Photo: J. Curtis Collisionally-induced fluorescence Temporal evolution of emitted photons can be observed. This is collisionally-induced fluorescence from electrons raining down upon neutrals. Comet Hale-Bopp. Photo: D. Toohey Ultraviolet-induced fluorescence Visible and near-visible photons can provide nonintrusive diagnosis of plasmas. Blue comet plasma tail is visible due to fluorescence induced by ultraviolet photons from the Sun. White tail is sunlight scattered from comet dust tail. When light travels through matter, it is slowed down by the electrons in the atoms. Different frequencies/wavelengths are slowed different amounts depending on the atoms in the material. Prism of quartz example below. Diamonds have very strong wavelength dependence (spread the colors a lot) and are very durable (Zircon nearly as good). Leaded glass is great, too. Now let’s go look at some fun atmospheric light effects http://www.atoptics.co.uk Rainbow – large drops (refraction, reflection) primary, secondary, higher, supernumerary (wave interference) Corona – small drops (diffraction) Glory and Heiligenschein (not same) Halo – parhelic circle, sun dog, tangential arc Green flash Corona are caused by diffraction around small water mist in the atmosphere. Typically seen around 15 degrees from the sun or moon. Can have rainbowlike color spread. What is a laser; why do we care to know? • Light Amplification of Stimulated Emission Radiation (LASER). Often laser light is: – Aimed pretty much in one direction, – Pretty much near one wavelength (color) • Lasers are described by Maxwell’s Equations, with a little bit of quantum mechanics thrown in. • There are lasers in nature, but most interest is for business purposes. And, lasers are big business. Theodore Maiman (my mother was acquainted with him) got the patent for the first laser. Maiman with a ruby laser on the laser’s 25th anniversary. Photo courtesy of Kathleen Maiman 1960 invention 1961 patent application 1967 patent issued A double Laser-Induced Fluorescence (LIF) system: Two pump plasma ion lasers, in background, drive two tunable dye lasers (one with cover removed). (This photo is 15 years old, but was hard to make; we are not doing it again). How your airplane follows its flight path Subtitle: Ring laser gyroscopes, plasma etching, the US Supreme Court, and Doctrine of Equivalents, which may put you in a fog (fiber optic gyroscope). Author: Willy Makeit Illustrator: Betty Wont In 1978 a man and his dog found a way to make incredibly-highly reflecting mirrors. He did not know why this way worked and the dog would not say, but Litton Industries was very happy. Among the pleasant people assembled for the Litton team was attorney John Roberts. You know him now as Chief Justice of the US Supreme Court. Tissue Discrimination via LIF Purpose • To find a practical, inexpensive, and noninvasive method of discriminating healthy from unhealthy biological tissue Picture by Medicine Net <http://www.medicinenet.com/images/illustrations/skin.jpg> Hopes and Dreams • Fluorescence on human skin might be done without damage • Fluorescence might allow discrimination of different types of skin conditions and growths • Perhaps various skin cancers can be detected by fluorescence instead of skin biopsy technique presently used • Potential for much lower cost, very fast analysis while the patient is in the office, and no biopsy wound requiring healing And finally, how do lasers and plasmas help you use the internet? Optical fibers carry your conversations to their destinations • Your voice is converted into pulses of light traveling down “light tubes” called optical fibers. • Fibers are especially useful for long lines, like from US to Japan. • Still, while traveling on long lines, the signal gets weaker and needs to be amplified occasionally. • Putting atoms which can lase directly into the fiber allows the fiber to become the amplifier. Erbium-doped Fiber Amplifiers (EDFA) can give you clear communication anywhere a fiber can be run On the 1550 nm voice signal where one might want a stable, low-power laser source • UC Irvine worked with New Focus to develop small, inexpensive tunable, stable diode lasers. • New Focus was another Milton Chang startup (like Newport Corporation). • New Focus now owned by Bookham Technologies (whose president worked for me in graduate school). New Focus laser in blue box in middle. Note how small it is compared to person in photo. On the 980 nm amplifying laser pump power where one might want a stable, high-power laser source • UC Irvine worked with SDL to develop 0.5W single-pass diode laser amplifiers. SDL MOPA with diffraction grating cavity removed. The 0.5 W output active semiconductor chip diode is white dot in center of gold holder. Chip is about 2 mm wide. Shakespeare’s King Henry VI, Part III, Act II, Scene I EDWARD: Dazzle mine eyes, or do I see three suns? RICHARD: Three glorious suns, each one a perfect sun; Not separated with the racking clouds, But sever'd in a pale clear-shining sky. See, see! they join, embrace, and seem to kiss, As if they vow'd some league inviolable: Now are they but one lamp, one light, one sun. In this the heaven figures some event. Conclusions • Every person in this room is relying on electromagnetism around the clock for their participation in civilization. • The lighter side of physics is fun to observe and understand.
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