jtotheizzoe:

explore-blog:

Yesteryear’s stereotype-defiers: Kick-ass vintage public domain photos of women in science.

Rock on, ladies!! Decades of inspiration here.

anndruyan:

Electric Field Due to a Uniformly Charged Disk 

Perhaps one of the most difficult concepts in general physics is uniformly charged surfaces. Really, I can’t think of anything more rigorous than E&M and complex integration.

Usually with these problem sets we are given the task of finding the E field at a distance and/or the E field when two charges are in the system.

So when given a uniformly charged disk and asked to find the E field at a distant point here’s how we do it:

First we need to divide the disk into flat rings so we can calculate the E field at our point P by adding up all the rings. Each ring will be out at a distance y and will have a radial width of dy. 

Next we’ll set up the E field equation E=kQ/r², but write it as dE=kdQ/√(x² + y²).

Now we come to our first tricky part of E field integration; the dQ. When we do these problems we must remember our charge densities - linear, surface, volume; lambda, sigma, and rho respectively. 

• Linear - lambda, 1 dimension : dQ = λdx
• Surface - sigma, 2 dimensions : dQ = σdA
• Volume - rho, 3 dimensions : dQ = ρdV

Here, we use sigma and use the relationship dQ = σdA = σ2πydy. All that means is that our charge, dq, is equal to the surface charge density, σ, times the area of the charged concentric ring.  

Now that we have our charge set we can look at the x and y components of the E field. If you look at dE_y you’ll see that as you go around the ring there is another y component that cancels each other out. Therefore we only focus on dE_x since the vector sum of dE_y will add to 0. 

Our dE_x = kdQ cosθ /(x² + y²). We use cosθ because on our free-body diagram dE_x is the adjacent-hypotenuse component of dE. Further substitute the dE_x equation by using x/√(x² + y²) for cosθ  and 1/4πε for k.

Only thing left to worry about is your trig identities of integration. Take the integral of dE_x from 0 to R and you will find the E field at point P. 

journeyofscience:

Jest to jedna z tych notek, które chciałem napisać już od dawna. Zarówno życiorys Tesli jak i Edisona byłby świetnym materiałem na artykuł. Jednak losy tych dwóch największych wynalazców XX wieku są tak blisko ze sobą powiązane, że nie sposób je rozdzielić. Zapraszam na naprawdę elektryzujący artykuł o wojnie między dwoma wynalazcami.

Źródło obrazka: http://mmcelhaney.blogspot.com/2011/09/tesla-vs-edison-g4tvcom.html

Nikola Tesla już w dzieciństwie przejawiał zamiłowanie do majsterkowania. Mając dziewięć lat zbudował swój pierwszy silnik, napędzany siłą mięśni chrabąszczy. Na Politechnice w Grazu, a później na Uniwersytecie Praskim Tesla zaskakiwał swoich profesorów.

W międzyczasie Thomas Edison zainteresował się żarówką, którą 19 lat wcześniej wymyślił i opatentował Joseph Swan (tak, tak - to nie Edison wymyślił żarówkę). Świeciła ona zaledwie kilka minut. Edison wymyślił, że gdyby udało mu się przedłużyć czas palenia żarówki to mógłby na tym nieźle zarobić. Celem było znalezienie materiału, który będzie się żażył przez długi czas, ale nie zapali się i nie spłonie (do tego wystarczy wytworzyć próżnię w bańce szklanej). Edison sprawdził około 6 - 8 tysięcy substancji. A tak na prawdę nie tyle on, co jego podwładni. Edison już wówczas miał sporo pieniędzy i stać go było na opłacenie pracowników od czarnej roboty. Najlepszym materiałem okazała się zwęglona bawełna, która żarzyła się 40 godzin.

To jednak było za mało, a Edison potrzebował więcej pieniędzy na badania. Przystroił zatem światełkami swój dom i na święta Bożego Narodzenia zaprosił na przedstawienie śmietankę biznesu. Goście oniemieli na ten widok i Edison nie miał problemu ze zebraniem odpowiedniej ilości gotówki. Niedługo potem żarówka z zwęglonym włóknem bambusa żarzyła się już 400 godzin. Edison wybudował pierwszą na świecie elektrownie i zaczął ludziom sprzedawać prąd, żarówki, oprawki, włączniki, liczniki… Podczas gdy jego pracownicy liczyli każdy grosz, on dorobił się majątku.

Z elektrownią Edisona był pewien problem. Potrafiła wysyłać prąd jedynie na krótkie odcinki, a i tak straty energii były ogromne. Tesla znalazł rozwiązanie tego problemu. Postanowił w tym celu udać się osobiście do Edisona. Pierw znalazł pracę w firmie w Budapeszcie, która przyjaźniła się z koncernem Edisona. Następnie poprosił szefa o list polecający. Z czterema centami w kieszeni wszedł na pokład statku płynącego do Nowego Jorku. Gdy był już na miejscu pokazał Edisonowi list, w którym było napisane: “Drogi Panie Edisonie, znam dwóch wielkich ludzi i pan jest jednym z nich. Drugim zaś jest ten młody człowiek, który stoi przed panem.”

Edison chciał przetestować Tesle i zlecił mu wykonanie niemożliwego zadania. Miał on usprawnić konstrukcję dynama Gramme’a. Jeśli by to mu się udało, to otrzymałby od Edisona 50 tys dolarów (czyli na dzisiejsze 1 000 000 $). Tesla mając środki i możliwości skonstruował swój pomysł - generator prądu przemiennego. Umożliwiał on przesył prądu na właściwie dowolne odległości przy minimalnej stracie energii. Okazał się on 50% bardziej wydajny od dynama Gramme’a. Mimo tego Edison odmówił wypłacenia pieniędzy mówiąc: “Wy Europejczycy nigdy nie zrozumiecie naszego amerykańskiego poczucia humoru”.

Nowy rodzaj prądu nie spodobał się Edisonowi prawdopodobnie dlatego, że oznaczało ono konieczność przebudowy elektrowni i sieci przesyłowej, w którą wpakował już dużo pieniędzy.

Wielki potencjał w młodym naukowcu ujrzał milioner George Westinghouse. Zaproponował on Tesli 60 tys $ za prawa do patentów (z czego tylko 5 tys gotówką). Zgodził się on, mimo tego, że na jego patentach Westinghouse zarobi potem grube miliony. Tesli z resztą nigdy nie chodziło o pieniądze. Miał on wyższe cele… ale o tym później.

Sukces systemu Tesli spowodował gwałtowny wzrost cen miedzi. To zabolało kieszeń Edisona, który potrzebował ogromnych ilości tego materiału do budowy nowej elektrowni co dwa kilometry. Wściekł się. Postanowił przeprowadzić kampanię, po której przeciętny Amerykanin zacznie się bać wynalazku Tesli. Z okolic zaczęły ginąć zwierzaki. Edison bowiem zaczął płacić dzieciakom 25 centów za przynoszenie zwierzaków, które następnie uśmiercał publicznie przy pomocy wynalazku Tesli. Przy tej okazji wymyślił także (i opatentował) krzesło elektryczne. Pierwszym skazanym straconym na krześle był William Kemmler, który zamordował swoją konkubinę siekierą. Przy pierwszej próbie egzekucja się nie udała. Kemler był rażony prądem przez 20 sekund, a mimo to przeżył. Podniesiono napięcie do dwóch kilowoltów, ale trzeba było czasu, aby ponownie naładować generator. W tym czasie ofiara męczyła się niemiłosiernie. Druga próba trwała minutę. Cała scena była opisywana przez świadków jako przerażająca.

Tesla jako człowiek bez umiejętności interpersonalnych, nie umiał sobie poradzić z atakami Edisona. Pomagał mu w tym Westinghouse, który przekonał innych milionerów i wybudowali elektrownie wodną nad wodospadem Niagara. Energie wysłali 40 kilometrów dalej do miasta Buffalo. Edison po tym sukcesie skapitulował. Mimo to zawiść między tymi wynalazcami kwitła. Gdy w 1915 roku Agencja Reutera podała, że Nagroda Nobla zostanie w tym roku zostanie podzielona między Tesle a Edisona. Oboje zakomunikowali, że w takim razie jej nie przyjmą.

Tesla wymyślił także radio. Jednak Guglielmo Marconi wyprzedził go w urzędzie patentowym. W walce o palmę pierwszeństwa wspierał go Edison i milioner Andrew Carnegie. Tesla wytoczył procesy sądowe przeciwko Marconiego o bezprawne użycie jego 17 patentów. Procesy toczyły się w nieskończoność co doprowadziło Tesle do bankructwa. Dodatkowo przyznanie nagrody Nobla Marconiemu za wymyślenie radia wpędziło Tesle w depresje. Kilka lat po śmierci Tesli Sąd Najwyższy USA przyznał mu prawo do patentu radia. Nie może tu jednak być mowy o sprawiedliwości historycznej. Po prostu Stany Zjednoczone używały radia podczas drugiej wojny światowej. Po wygraniu wojny Marconi upomniał się o należność za wykorzystanie jego wynalazku. USA po prostu zamiast płacić, zdecydowały się przyznać patent nieżyjącemu już Nikoli Tesli.

Tesla wymyślił również wiele innych wynalazków, które nie przypisuje się jemu. Na przykład za wynalazcę radaru uznaje się Roberta Watsona-Watta (1935). Podczas gdy w 1917 roku podczas I wojny światowej, swój radar Tesla przedstawił marynarce Stanów Zjednoczonych. Niestety szefem jednostki badawczo-rozwojowej marynarki w ówczesnych czasach był… Thomas Edison, który uznał wynalazek za bezużyteczny. Innym przykładem są promienie X, które Tesla wymyślił przed Rontgenem. Postulował też istnienie sztucznego promieniowania na długo przed Marią Curie-Skłodowską.

Marzeniem Nikola Tesli była bezprzewodowa transmisja energii. Marzył, że któregoś dnia prąd będzie dostępny dla każdego za darmo. Swoje marzenia próbował zrealizować. Naturalnie nie spodobało się to bogaczom, którzy przestali finansowo wspierać Tesle. Dopiero w 2007 roku udało się dokończyć jego prace fizykom z MIT.

Z okazji 70 rocznicy śmierci Nikoli Tesli.

ihititwithmyaxe:

Science!, simplified.

brookhavenlab:

This gorgeous shot of the complexity that is the STAR detector at Brookhaven comes from amateur photographer Enrique Diaz, who won our recent photography competition. 

Two months ago, Brookhaven National Lab invited 50 amateur and professional photographers to a three-hour, behind-the-scenes tour of the laboratory. Our cutting-edge experiments explore the fringes of fundamental science and represent singular achievements in design and engineering, and these photographers lent their considerable talent to capturing these marvels and showing off the beauty of science. 

We received more than 100 stunning submissions that revealed our facilities through fresh eyes, and we’ll be featuring a few of the Top 10 here throughout the next week.

howstuffworks:

From How Electricity Works:

Even though they didn’t fully understand it, ancient people knew about electricity. Thales of Miletus, a Greek philosopher known as one of the legendary Seven Wise Men, may have been the first human to study electricity, circa 600 B.C. By rubbing amber — fossilized tree resin — with fur, he was able to attract dust, feathers and other lightweight objects. These were the first experiments with electrostatics, the study of stationary electric charges or static electricity. In fact, the word electricity comes from the Greek elektron, which means amber.

The experiments wouldn’t continue until the 17th century. That’s when William Gilbert, an English physician and amateur scientist, began to study magnetism and static electricity. He repeated the research of Thales of Miletus, rubbing objects together and charging them by friction. When one object attracted or repelled the other, he coined the term “electric” to describe the forces at work. He said these forces developed because the rubbing action removed a fluid, or “humour,” from one of the objects, leaving an “effluvium,” or atmosphere, around it.

This concept — that electricity existed as a fluid — persisted into the 1700s. In 1729, English scientist Stephen Gray observed that certain materials, such as silk, didn’t conduct electricity. His explanation was that the mysterious fluid described by Gilbert could travel through objects or be hampered from traveling. Scientists even built jars to hold this fluid and study its effects. The Dutch instrument makers Ewald von Kleist and Pieter van Musschenbroek created what is now known as a Leyden jar, a glass jar containing water and a nail that could store an electrical charge. The first time Musschenbroek used the jar, he received a massive shock.

Keep reading…

kateoplis:

Fermilab’s 570-megapixel Dark Energy camera captures first images

quantumaniac:

First Practical Maser (Microwave Laser) Built

Using spare chemicals, a laser bought on eBay and angst from a late-night argument, physicists have got the world’s first room-temperature microwave laser working. The achievement comes nearly 60 years after the first clunky versions of such devices were built, and could revolutionize communication and space exploration. The work is published this week in Nature.

Before there were lasers, there were microwave lasers, or masers. First conceived in the Soviet Union and the United States during the 1950s, early maser machines were the size of a chest of drawers. They produced only a few nanowatts of power, severely limiting their usefulness.

Because of this impediment, most in the field gave up on masers and moved on to lasers, which use the same principles of physics, but work with optical light instead of microwaves. Lasers are now used in applications ranging from eye surgery to CD players. The poor maser lived on in obscurity. It found only a few niche uses, such as boosting radio signals from distant spacecraft — including NASA’s Curiosity Mars rover. Those masers work only when cooled to less than ten degrees above absolute zero, and even then they are not nearly as powerful as lasers.

Pink power
But Mark Oxborrow, a physicist at the UK National Physical Laboratory in Teddington, wondered whether a crystal containing the organic molecule pentacene might offer a breakthrough. He came across a decade-old publication by Japaneseresearchers suggesting that when the electrons in pentacene are excited by a laser, they configure such that the molecule could work as a maser, possibly even at room temperature.

He borrowed some spare pentacene from a lab at Imperial, and cooked it with another organic molecule known as p-terphenyl. The result was a pink crystal a few centimeters long.

Next, the team needed a powerful laser. Oxborrow located an old medical laser on eBay and drove to a warehouse in north London to pick it up. But the researchers were filled with doubts — the whole thing seemed too easy. Oxborrow admits that he was skittish about the experiment. “For about three days, I could have done it, but I didn’t have the nerve to switch on that button,” he says.

The final impetus came from an argument with his wife. Whereas less well-behaved people might have wallowed in the pub, “I went to the lab as a bit of therapy”, says Oxborrow. “I said, ‘Oh well, what the hell, let’s just try it.” And it worked on the first go.

Excited state
The laser light excited the pentacene molecules to an energy level known as a metastable state. Then a microwave passing through the crystal triggered the molecules to relax, releasing a cascade of microwaves of the same wavelength.

It was the same principle as an optical laser. “The signal that came out of it was huge,” says Oxborrow, about a hundred million times as powerful as an existing maser. Alone in his lab, “I swore a lot and walked around the corridor about five times talking to myself”.

Left: New maser

Right: A Hydrogen Radio Frequency Discharge (early Maser)

sciencesoup:

The Resolution of the Human Eye

In an age of ever-improving technology, the question of the human eye’s resolution is more interesting than ever. Resolution is the ability to see two sources very close together, and is measured in arcminutes, with 60 arcminutes in a degree. The further away two objects are, the smaller the angle separating them—for example, the Hubble Space Telescope has a resolution of 0.0008 arcminutes, which means that if two stars are closer together than that, they appear as a single object. The resolution limit of the human eye varies from person to person, but if you had 20/20 vision your resolution would be 0.6 arcminutes. Our vision isn’t like an image, though; it’s more like a constant video stream, with our eyes moving rapidly and constantly updating the images we see, so the resolution of the human eye is far greater than any camera—it’s the equivalent of 576 megapixels. Potentially, a 576 megapixel image could fool our eyes into thinking it was the real thing, but only if you covered one eye—as soon as both eyes move, you’d be able to detect that the image was flat, not 3D. Intriguing stuff.

everlane:

An alarming visualization of when the Earth’s non-renewable resources will run out from the BBC. 

crookedindifference:

Tycho Brahe, in his Astronomiæ instauratæ mecanica (Wandsbek 1598), shows how to mount the sextant to measure the elevation of celestial objects

ihateallyourgods:

Much better

thescienceofreality:

1.  Chaos: Making a New Science - James Gleick: “James Gleick’s bestseller introduces the story of one of the most significant waves of scientific knowledge in our time. Gleick makes chaos theory not only fascinating but also accessible, and opens our eyes to a surprising new view of the universe. “
2.  Free Will - Sam Harris:  ”It is difficult to think about law, politics, religion, public policy, intimate relationships, morality—as well as feelings of remorse or personal achievement—without first imagining that every person is the true source of his or her thoughts and actions. And yet the facts tell us that free will is an illusion.”
3.   A Brief History of Time - Stephen Hawking: “Stephen Hawking’s book explores such profound questions as: How did the universe begin—and what made its start possible? Does time always flow forward? Is the universe unending—or are there boundaries? Are there other dimensions in space? What will happen when it all ends?”
4.  The Black Swan: The Impact of the Highly Improbable - Nassim Nicholas Taleb: “A black swan is an event, positive or negative, that is deemed improbable yet causes massive consequences. In this groundbreaking and prophetic book, Taleb shows in a playful way that Black Swan events explain almost everything about our world, and yet we—especially the experts—are blind to them.”
5.  The Selfish Gene - Richard Dawkins: “Richard Dawkins’ brilliant reformulation of the theory of natural selection has the rare distinction of having provoked as much excitement and interest outside the scientific community as within it. His theories have helped change the whole nature of the study of social biology.”
6.  A Primate’s Memoir: A Neuroscientist’s Unconventional Life Among the Baboons - Robert M. Sapolsky: “ ‘I had never planned to become a savanna baboon when I grew up; instead, I had always assumed I would become a mountain gorilla,’ writes Robert Sapolsky in this witty and riveting chronicle of a scientist’s coming-of-age in remote Africa.”
7.  Cosmos - Carl Sagan: “The best-selling science book ever published in the English language, COSMOS is a magnificent overview of the past, present, and future of science. Brilliant and provocative, it traces today’s knowledge and scientific methods to their historical roots, blending science and philosophy in a wholly energetic and irresistible way.”
8.  Godel, Escher, Bach: an Eternal Golden Braid - Douglas Hofstadter: “This book concerns the nature of “maps” or links between formal systems. However, according to Hofstadter, the formal system that underlies all mental activity transcends the system that supports it. If consciousness can emerge out of a formal system of firing neurons, then so too can computers attain human intelligence.”
9.  Ideas and Opinions - Albert Einstein: “A collection of Albert Einstein’s popular writings, gathered under the supervision of Einstein himself. The selections range from his earliest days as a theoretical physicist to his death in 1955; from such subjects as relativity, nuclear war or peace, and religion and science, to human rights, economics, and government.”
10.   Wider than the Sky: the phenomenal gift of consciousness - Gerald Edelman: “Edelman puts forward the theory of neuronal group selection, also known as Neural Darwinism. The book also makes a distinction between primary consciousness and higher-order consciousness.”
11.  What Do You Care What Other People Think? - Richard Feynman: “This volume presents the adventures of the Nobel Prize-winning physicist Richard Feynman. Readers learn the inner workings of the Rogers Commission, the stupifying realities of bureaucratic obfuscation, and the confusion and misjudgement that have plagued NASA in recent years.”
12.  Primates and Philosophers: How Morality Evolved - Frans de Waal: ““It’s the animal in us,” we often hear when we’ve been bad. But why not when we’re good? Primates and Philosophers tackles this question by exploring the biological foundations of one of humanity’s most valued traits: morality.”
13.  Thought Contagion: How Belief Spreads Through Society (The New Science of Memes) - Aaron Lynch: “This book explores the notion that an idea which can influence human behavior may blindly evolve the capacity to influence its own prevalence in the human population by motivating its human hosts to engage in behavior that spreads the idea.”
14.  The Oxford Book of Modern Science Writing - Richard Dawkins: “Boasting almost one hundred pieces, The Oxford Book of Modern Science Writing is a breathtaking celebration of the finest writing by scientists—the best such collection in print—packed with scintillating essays on everything from “The Discovery of Lucy” to “The Terror and Vastness of the Universe.””
15.  The Most Human Human: What Talking with Computers Teaches Us About What it Means to be Alive - Brian Christian: “Each year, the AI community convenes to administer the famous Turing test, pitting sophisticated software programs against humans to determine if a computer can “think.” The machine that most often fools the judges wins the Most Human Computer Award. But there is also a prize, strange and intriguing, for the “Most Human Human.””
16.  Thinking, Fast and Slow - Daniel Kahneman: “A tour of the mind that explains the two systems that drive the way we think. System 1 is fast, intuitive, and emotional; System 2 is slower, more deliberative, and more logical. Kahneman exposes the extraordinary capabilities—and also the faults and biases—of fast thinking, and reveals the pervasive influence of intuitive impressions on our behavior.”
17.  Death by Black Hole and other Cosmic Quandaries - Neil deGrasse Tyson: “Here, Tyson compiles his favorite essays across a myriad of cosmic topics. The title essay introduces readers to the physics of black holes by explaining the gory details of what would happen to your body if you fell into one.”
18.  Tipping Point: How Little Things can make a Big Difference: “The tipping point is that magic moment when an idea, trend, or social behavior crosses a threshold, tips, and spreads like wildfire. Just as a single sick person can start an epidemic of the flu, so too can a small but precisely targeted push cause a fashion trend, the popularity of a new product, or a drop in the crime rate.”
19.  From Poison Arrows to Prozac: How Deadly Toxins Changed Our Lives Forever: “Curare poison, first used to tip the arrows of native South Americans,  was to become the cornerstone of modern anesthetics and went on to provide the key to how we understand the nervous system, leading to drugs as diverse as indigestion pills and Prozac. More recently it has led to our understanding of Alzheimer’s and Parkinson’s disease.”
20.  The Theory That Would Not Die - Sharon Bertsch McGrayne: “Bayes’ rule appears to be a straightforward, one-line theorem: by updating our initial beliefs with objective new information, we get a new and improved belief. To its adherents, it is an elegant statement about learning from experience. To its opponents, it is subjectivity run amok.”
21.  Napoleon’s Buttons: How 17 Molecules Changed History - Penny Le Couteur : “This is the fascinating account of seventeen groups of molecules that have greatly influenced the course of history.”
22.  The Emperor of all Maladies: A Biography of Cancer - Siddhartha Mukherjee: “A magnificent, profoundly humane “biography” of cancer—from its first documented appearances thousands of years ago through the epic battles in the twentieth century to cure, control, and conquer it to a radical new understanding of its essence. Physician, researcher, and award-winning science writer, Siddhartha Mukherjee examines cancer with a cellular biologist’s precision, a historian’s perspective, and a biographer’s passion.”
23.  Freakonomics: A Rogue Economist Explores the Hidden Side of Everything - Steven Levitt & Stephen Dubner: “Which is more dangerous, a gun or a swimming pool? What do schoolteachers and sumo wrestlers have in common? How much do parents really matter? These may not sound like typical questions for an economist to ask, but Freakonomicsstudies the riddles of everyday life and reaches conclusions that turn conventional wisdom on its head. ”
24.  Hyperspace - Michio Kaku: “A roller coaster of an intellectual ride through the extraordinary world of black holes, wormholes, parallel universes, higher dimensions and time travel.”
25.  Musicophilia: Tales of Music and the Brain - Oliver Sacks: “Music can move us to the heights or depths of emotion. It can persuade us to buy something, or remind us of our first date. It can lift us out of depression when nothing else can. It can get us dancing to its beat.  But the power of music goes much, much further. Indeed, music occupies more areas of our brain than language does—humans are a musical species.”

mothernaturenetwork:

5 things your brain does better than a computer