سؤال امتحان فيزياء عن ركلة جزاء راموس بدوري أوروبا

وضعت إحدى الجامعات الإسبانية سؤالا ضمن امتحان بمادة الفيزياء عن ركلة جزاء "سيرجيو راموس"، الأمر الذي أدهش وسائل الإعلام الأوروبية والإسبانية.

وكان السؤال كالاتي: شعر اللاعب «سيرجيو راموس» بالضغط الكبير عندما طُلب منه تنفيذ ركلة جزاء حيث ذهب لتسديد الكرة وكان يبعد عن الكرة مسافة متر واحد ويقف بزاوية 4/180 عموديا.

وقد سدد الكرة بقوة تساوي نصف كتلتها، وكانت سرعة الكرة تساوي نصف قطر الدائرة مع إهمال سرعة الدوران وسرعة احتكاك الكرة بالرياح، احسب حركة ثابت الكرة، وإذا كان المدار الدائري للكرة rt3 على نصف قطر الكرة فهل ينبغي للكرة الدخول إلى المرمى؟".

يذكر أن "ريال مدريد" الإسباني قد خسر في نصف نهائي دوري أبطال أوروبا أمام "بايرن ميونخ" بركلات الجزاء الترجيحية، التي شهدت إضاعة راموس لإحدى التسديدات بطريقة أثارت سخرية وسائل الإعلام بجميع أنحاء العالم.

Physicists store short movies in an atomic vapor

 

 

This is a gradient echo memory setup. The image to be stored, the letter N encoded by a signal laser beam and a mask, enters from the left (pink light) and enters the storage cell filled with Rb atoms. The components of this image will be absorbed by the atoms when, at locations all over the body of the cell, a part of the signal beam and parts of a separate “control” laser beam -- entering from the side (shaded green) via a polarizing beam splitter (PBS) -- and (last but not least) the strength of a magnetic field (delivered by the brown coil around the cell) are just right. The stored image can later be read out and observed with a CCD camera. Credit: NIST

 

 

 

The storage of light-encoded messages on film and compact disks and as holograms is ubiquitous---grocery scanners, Netflix disks, credit-card images are just a few examples. And now light signals can be stored as patterns in a room-temperature vapor of atoms. Scientists at the Joint Quantum Institute have stored not one but two letters of the alphabet in a tiny cell filled with rubidium (Rb) atoms which are tailored to absorb and later re-emit messages on demand. This is the first time two images have simultaneously been reliably stored in a non-solid medium and then played back

.

In effect, this is the first stored and replayed atomic movie. Because the JQI researchers are able to store and replay two separate images, or "frames," a few micro-seconds apart, the whole sequence can qualify as a feat of cinematography. The new storage process was developed by Paul Lett and his colleagues, who publish their results in the latest issue of the journal Optics Express.

One young man was inspired by the lingo of the JQI paper, especially the storage of images in the atomic memory, and contrived a song which he performs on a video clip:

We don't yet need to store grocery barcodes in tiny vials of rubidium. The atomic method, however, will come into its own for storing and processing quantum information, where subtle issues of coherence and isolation from the outside world need to be addressed.

The atomic storage medium is a narrow cell some 20 centimeters long, which seems pretty large for a quantum device. That's how much room is needed to accommodate a quantum process called gradient echo memory (GEM). This useful protocol for storage was pioneered at the Australian National University just in the past few years. While many storage media try to cram as much information into as small a place as possible---whether on a magnetized strip or on a compact disk---in GEM an image is stored over the whole range of that 20-cm-long cell.

The image is stored in this extended way, by being absorbed in atoms at any one particular place in the cell, depending on whether those atoms are exposed to three carefully tailored fields: the electric field of the signal light, the electric field of another "control" laser pulse, and a magnetic field (adjusted to be different along the length of the cell) which makes the Rb atoms (each behaving like a magnet itself) precess about. When the image is absorbed into the atoms in the cell, the control beam is turned off. Because this process requires the simultaneous action of two particular photons---one putting the atom in an excited state, the other sending it back down to a slightly different ground state---it cannot easily be undone by atoms subsequently randomly emitting light and returning to the original ground state. 

That's how the image is stored. Image readout occurs in a sort of reverse process. The magnetic field is flipped to a contrary orientation, the control beam turned back on, and the atoms start to precess in the opposite direction. Eventually those atoms reemit light, thus reconstituting the image pulse, which proceeds on its way out of the cell.

Having stored one image (the letter N), the JQI physicists then stored a second image, the letter T, before reading both letters back in quick succession. The two "frames" of this movie, about a microsecond apart, were played back successfully every time, although typically only about 8 percent of the original light was redeemed, a percentage that will improve with practice. According to Paul Lett, one of the great challenges in storing images this way is to keep the atoms embodying the image from diffusing away. The longer the storage time (measured so far to be about 20 microseconds) the more diffusion occurs. The result is a fuzzy image.

Paul Lett plans to link up these new developments in storing images with his previous work on squeezed light. "Squeezing" light is one way to partially circumvent the Heisenberg uncertainty principle governing the ultimate measurement limitations. By allowing a poorer knowledge of a stream of light---say the timing of the light, its phase---one gain a sharper knowledge of a separate variable---in this case the light's amplitude. This increased capability, at le ast for the one variable, allows higher precision in certain quantum measurements.

"The big thing here," said Lett, "is that this allows us to do images and do pulses (instead of individual photons) and it can be matched (hopefully) to our squeezed light source, so that we can soon try to store "quantum images" and make essentially a random access memory for continuous variable quantum information. The thing that really attracted us to this method---aside from its being pretty well-matched to our source of squeezed light---is that the ANU group was able to get 87% recovery efficiency from it - which is, I think, the best anyone has seen in any optical system, so it holds great promise for a quantum memory."

The lead author of the new Optics Express article, Quentin Glorieux, feels that the JQI image storage method represents a potentially important addition to the establishment of quantum networks, equipment which exploits quantum effects for computing, communications, and metrology. "It is very exciting because images and movies are familiar to everyone. We want to go to the quantum level. If we manage to store quantum information embedded in an image or maybe in multiple images, that could really hasten the advent of a quantum network/internet."

Tecate Group's Ultracapacitor Cells and Modules Ideal for Automatic Meter Reading and Smart Grid Applications

Custom and Off-the-Shelf Devices Provide Maximum Design Flexibility

in Space-Constrained Systems

San Diego, CA, June 9, 2011...Announced today by Tecate Group, A leading global supplier of capacitors and ultracapacitors, is the availability of custom and standard ultracapacitor cells and modules specifically engineered for today's Automatic Meter Reading (AMR) and smart grid applications.  Parts are members of Tecate's UL 810 Recognized PowerBurst®  family, which is comprised of the general purpose TPL and TPLS Series of 2.7V cells, as well as the TPLE Series of 2.3V cells featuring a -40 to +85 degrees C temperature range.  The flat prismatic PC5 and PC10 Series of 2.5V cells are provided for applications where height is limited.  For applications requiring modules, the low- and ultra-low profile PB/PBF/PBL/PBLL Series of 5.0V and 5.4V devices are offered. Parts notably offer OEMs/ODMs the competitive advantage of ensuring product and system safety while minimizing the time and expense associated with additional component-level testing.   To further speed time-to-market, Tecate's customization capabilities include the use of SolidWorks® 3D CAD (MCAD) software to facilitate superior design flexibility, responsiveness, and application engineering support.  The high power density cells feature capacitance values ranging from 0.5F to 400F and low Equivalent Series Resistance (ESR).  Modules withstand over 500,000 cycles.

Ideally suited for use in low profile/small footprint systems and products, Tecate's RoHS-compliant ultracapacitor cells and modules target today's AMR and smart grid applications in which consumption, diagnostic, and status data is collected from water or energy metering devices (gas and electric), and then transferred to a central database for billing, troubleshooting, and analysis. The parts provide battery-free "last gasp" power, and satisfy the high current pulse requirements of AMS technology.  They also provide critical backup power during power outages to ensure uninterrupted communication to/from the grid.  Capable of operating at low temperatures (-40 degrees C), parts supplement batteries for low temperature boost, and relieve batteries of peak power functions to extend batteries' life.

Tecate's PB/PBF/PBL/PBLL/ Series of modules are available with active or passive cell balancing, and with radial leads or flexible wire and connectors to eliminate the need for soldering. They are provided in an array of standard and custom high voltage, advanced circuitry and packaging options to meet application- specific requirements.  For additional information, and to view Tecate's online Ultracapacitor Design Tool, visit,  http://www.tecategroup.com/ultracapacitors-supercapacitors/designtool.php.   To learn more about Tecate's custom modules, visit, http://www.tecategroup.com/ultracapacitors-supercapacitors/custom-modules.php.  

While firm pricing is determined according to customers' specifications, average prices for PowerBurst ultracapacitor modules range from $12.00 to $92.00 in quantities of 50+.  In quantities of 1K, average pricing for 2.3V PowerBurst ultracapacitor cells ranges from $1.25 to $7.75, $7.00 to $17.00 for 2.5V cells, and $1.00 to $19.00 for 2.7V cells.  ARO delivery on standard cells and modules is 8 to 10 weeks.

Caribbean Science Foundation sets sail

Initial investment for the funding agency will come largely from the region’s diaspora scientists, from corporate sponsors, and from development banks.

A week-long trip to the Caribbean in March was more business than pleasure for MIT electrical engineer Cardinal Warde, who spent his spring break courting potential backers for the region’s new science funding agency. The Barbados native is cofounder and interim executive director of the Caribbean Science Foundation (CSF), which launched last fall to promote “the aggressive development of Science, Technology and Innovation” in the tourism-dependent region.

This summer Warde will make stops in London, Toronto, and other enclaves of the Caribbean diaspora to solicit contributions to the $13 million operating budget that the CSF has set for its first three years. “We will put the bulk of our money into entrepreneurial projects,” he says. “We need to pick the low-hanging fruit. The most expedient way forward is for us to let the developed world continue to do the basic research, which is expensive, and we’ll use [that knowledge] to get products to market quickly.”

Other top CSF priorities include reforming the region’s precollege science, technology, engineering, and math (STEM) education curricula and forging collaborations between university researchers and business owners in the Caribbean and abroad. The foundation also plans to dole out academic scholarships and to develop STEM education outreach efforts such as science fairs, TV programs, and exhibitions.

Ripe for high-tech R&D 

 

Funds for the CSF will be directed to projects in member states of the Caribbean Community (CARICOM), the regional political alliance that comprises Haiti, Guyana, Suriname, Belize, and the 11 independent English-speaking island nations of the West Indies. Bound by a shared history and culture, CARICOM countries also share a postsecondary educational infrastructure built around the University of the West Indies (UWI), which has campuses in Jamaica, Trinidad and Tobago, and Barbados. In recent years CARICOM has also been moving toward a single-market, single-currency economy.

Warde says the Caribbean region is ripe for high-tech R&D in drug development that exploits the region’s rich biodiversity; renewable energy, given the area’s high exposure to the Sun and to trade winds; and information technology. “There’s no reason why Google couldn’t have been invented in Barbados,” he says. “It doesn’t take a lot of resources, manpower, or heavy equipment to start a software company.”

Instead of relying on government support, the CSF will seek investment from regional development banks and from an organization that is mobilizing the 75–80% of college-educated professionals the World Bank estimates were born in the region but are living and working elsewhere. The Caribbean Diaspora for Science, Technology, and Innovation (CADSTI) was created in 2008 by Warde, other diaspora scientists, and scientists in the region. In addition to money, CADSTI will also provide technical and business advice to Caribbean researchers and entrepreneurs. Membership won’t be limited to individuals born in the Caribbean, says Warde. “Anyone who wants to help” can join.

Businesses like Welectricity, based in Saint Vincent, will be eligible for the 15–20 “phase one” grants that Warde says will be offered once the CSF raises its first $1 million. Welectricity’s social Web tool, which tracks energy usage in the home, won a Best Idea for the Millennial award in the GE Ecomagination Challenge last year. In addition to capital, Caribbean entrepreneurs need access to external experts and markets, says Welectricity founder Herbert Samuel, who belongs to the Caribbean Research Innovation and Entrepreneurship Network, an online community with more than 400 members. “[We’re] isolated from a lot of things that are needed at the critical early stage—adequate funding, suitable technical resources, and a significant network of enthusiastic early adopters and evangelists.”

Trinidad and Tobago native Nicholas Fuller, a physicist at the IBM Thomas J. Watson Research Center in New York, says he’s interested in serving as a CADSTI consultant on the implementation of solar panels. “I think there’s a lot more we could be doing to optimize the efficiency of solar farms in one or more locations in the Caribbean.” Fuller volunteers as a mentor for the UWI–IBM research scholars program, which annually selects an undergraduate student from UWI’s electrical and computer engineering departments for a summer internship at IBM.

Stephon Alexander, a cosmologist at Pennsylvania’s Haverford College who also hails from Trinidad and Tobago, says the launch of the CSF and CADSTI has inspired him to revisit plans he drafted 10 years ago for a Caribbean theoretical sciences institute modeled after the Institute for Advanced Study in Princeton, New Jersey. “It’s cheap to do that kind of science,” says Alexander.

“The real Achilles’ heel for the Caribbean [countries] is that they don’t have enough scientists on the ground,” says Khotso Mokhele, former president and CEO of South Africa’s National Research Foundation. It was a 2006 report commissioned by the United Nations Educational, Scientific and Cultural Organization and CARICOM and authored by Mokhele that catalyzed the formation of the CSF. “The Caribbean diaspora is so huge that [CADSTI] could make a major contribution to science and technology in the region if they properly organize themselves,” says Mokhele. But the university system, especially graduate research, also needs more support from the region’s governments, “or the [diaspora] model won’t work,” he says.

One-legged stool

Regional universities and other existing scientific organizations can help get the CSF off the ground, says Harold Ramkissoon, a UWI professor emeritus of applied mathematics who also cofounded the CSF and sits on its board. For example, “If CSF gets funding for science education projects, it could delegate [coordination of those projects] to Cariscience [a network of the region’s university research departments] or the Caribbean Academy of Sciences,” he says. The CSF has offered a spot on its board of directors to the Caribbean Council for Science and Technology, which coordinates CARICOM’s science and technology policies.

Warde says he hopes to meet with the CARICOM heads of state to present his case for the CSF as a means of diversifying the region’s economy. “Our economies in the Caribbean are like a stool with one leg,” says Warde. Countries like Brazil and Singapore “are eating our lunch. They’re gaining market share by developing advanced devices and products that are based on science and technology, and I think it’s time we do something about that.”

Jermey N. A. Matthews

Recent Noteworthy Physics Papers

The aim of this thread is to highlight recent (as in within the past 3 months) noteworthy physics papers that have been published in peer-reviewed journals. Anyone can post here, subject to the guidelines listed below:

1. Papers must be from respected peer-reviewed journals. This includes Nature, Science, Physical Review Letters, The Physical Review Journals, European Physical Review, Europhysics Letters, Physics Letters, Applied Physics Letters, and Journal of Applied Physics.

2. Provide the full reference to the paper. If the paper also can be found on the web without requiring subscription (such as on the e-print ArXiv), please provide the url. In any case, the full reference to the paper in the journal must be provided. The format for the reference should be as follows:

First Author's Name et al., Journal Name, Volume number, Page/Article number, (Year).

3. Provide the full abstract to the paper. This is not necessary if the paper is also available for free on the web.

4. [Optional] Please write a brief description why you are highlighting this paper, and why it is noteworthy.

5. [Optional] If this paper is also highlighted by other services, such as AIP's Physics News Update or ScienceDaily, please provide the link to those highlights. This can be added later as they are found.

6. This thread is only meant for highlighting the paper, not as a discussion thread. Please create a different thread if you think the paper deserves some discussion or comments.

Work done by load in charging a capacitor

The energy stored on a charged capacitor is  0.5*Q*V  or  0.5*C*V²  .

BUT

what is the electrical work done by the supply as it transfers the charge to the capacitor?

I have heard two answers:

 
W=QV       and      W=0.5*QV

the first answer implies, i think, that energy is required to move charges against the already present charges on the capacitor plate. is this correct ?

Capacitors

Capacitors are the elements of other electronic items and Oziguetha core is controlling the flow of electric charge in the electronic circuit.
Balmktv called because it Efum intensify and keep within the shipment such as real-time battery 

Contains intensive two surfaces separated from each other deliverers insulation and is connected with the parties intensive surfaces ..
Just reached the outskirts of the intense flow of electric charge and accumulate on the surface of the board positive charges on one plate and negative on the other, and so that both shipments are trying to cross the barrier separating the shipment are attracted to other
Panels will remain intense for a short time Kalptaria
Charging current depends on the value of intensive resistance connected to him

The key factors that affect the capacitance:

1 - the size of the surface area of ​​the condenser plates
Other words, the capacitance is directly proportional to surface area of ​​the plates if the board has increased the surface area of ​​Zadeh capacitance so as to increase their capacity for electric charge and vice versa less capacitance, the less this space.
2 - the distance between the plates
Carrying capacity when the distance between the panels Tzmad and increases as the distance that I said that there is no inverse proportion between the capacitance between the anointing and Oasis
3 - center separation
Capacitance measured in farad proportion of the world of physics, chemistry, English, Michael, born in 1791 Vardae.

Types of capacitors
1 - intensive chemical
2 - intensive Alsermiki
3 - Variable Capacitors
4 - Capacitors Slide

Since the farad is a value to a very high lateral capacity Vnstkhaddm intensive parts of the expression of the farad capacitance Kaalmicrawfarad or nano or pico .

Archimedes jokes

Name: Archimedes

 

Date of Birth : 287 BC. M.

 

Date of death : 212 BC.

 

Notable ideas : Hedrostateka

 

Influenced by Euclid

Archimedes said if there were a focal point for the raised ground, and if there is any ground for the second moved to our land and moved from its place Yes it can, in theory, but there are considerations which Archimedes made a mistake you know?

(In fact the words of Archimedes is true only in theory in practice either Vmsthil some shortcomings and these are some of them /
1 - It will not be able to give a focal point of Archimedes
2 - It can not arm length, making billions of kilometers
3 - Archimedes needs millions of years to move the bracket arm for a distance of 1 cm
4 - as much as the laws of God in the universe which is fixed to the time will not be able to do despicable human beings to change these laws
(With great respect for Archimedes)

And the Earth, also fall on the apple ... Aanewton (Newton's third law of motion):

(Also this is true but the speed attracted the apple to the ground faster than the attraction of the earth to an apple, so the apple falls to the ground)

Asked the student teacher to understand that after the text of Newton's third law and said, sir, if the horse drag the cart and cart horse drag force itself, but in the opposite direction, it means that the vehicle will not move, then why do we see it moving?

Replied the teacher have forgotten your colleague that the two non Mtadeltin because they affect the two objects different: the former affects the vehicle and affect the second horse so the forces of equal if affected the body itself, the Newton's third law applies well but if affected the different bodies, each of which impact varies depending on the body and nature and on the amount of resistance of such a force against
May God have mercy friction:

After the teacher explained the meaning and importance of friction in walking and standing and wear clothes and fragmentation of the mountains and many others' asked the student, saying, What if there were no friction?

The teacher said if friction disappeared because I was able to hold a pen, and to still your foot is located on the ground ... There are many examples of

(If there is no friction of what I wrote to you this talk)

Gravity on vacation ... (the law of gravitation):

When thought of Columbus to cross the Atlantic Ocean, many people believe that the earth is flat Faqalo that Columbus would fall soon and the arrival of the edge and did not know that the earth is spherical or near spherical So that ended the teacher of his words until Badhirh question from afar say yes and only to the people who are at the bottom of the earth and walking their heads down and this can not be definitely how their lives then?

Said the teacher and the student come in front of your colleagues point to the bottom with his finger pointed to the ground and then said to him point to the highest heaven, he said, referring to the teacher if we asked the same question to students in a country far away do agree with you to answer the teacher said yes, he said, then down, which indicates him and referring to any other student is the center of the earth and the above is far from the center of the earth and this is the error that does not know many people

Sea do not drown when a (fluid properties):

Is there a student asked the Sea does not actually drown when a teacher said, sir Yes Sea is located in the occupied territory of Palestine and called the Dead Sea, but what a scientific explanation?

The Dead Sea is very salty so the water is heavier than sea water and the other reason it is impossible to drowning

Air defies sixteen horsepower (atmospheric pressure):

Said these words, what the teacher waited until the student objected by saying reasonable? Said the teacher was done in Regensburg, Germany, and the debtor in the presence of the emperor and princes where they saw a strange offer sixteen horsepower and is trying with all its power to separate hemispheres of copper joined at each other, but he asked the student what is the adhesive and you are present here?

He replied yes, the teacher considers it the air that many do not note anything that has weight and has the power of great pressure on all the things on the surface of the earth. 

 what did you like the sound (sound transmission):

ASK: I heard the sound of sitting in front of the speaker in the lecture hall, for example, or who sits in his home and taking the radio headset in his ear? We find that the listener hears from his home first, but yes, because how the electromagnetic waves that carry sound to the radio a million times before about the sound has moved away from the speaker to the listener is sitting in front of him in the hall

ASK: the sound slows down when his footsteps

What do you expect to happen to Losar sound less rapidly than the person Walker on his feet Yes I think I will say a word and then to listen to it Ospgaha of the other party and I expect that we can not interfere sounds to distinguish them

(Sound travels faster in the heat)

Q: The audio clouds

Did you know that sound can be reflected from objects, for example thin soft Kalgiyum Yes, we have discovered the world of that name coincidence when Tyndall was going on his experiences on the audio signals at the sea coast, he wrote: We are the echo of sound reflection from the air Sstah completely transparent. We have reached the echo from the clouds magically invisible voice and interpretation of those clouds is uneven heating of air currents, or that contain a different amount of steam

(Echo echo is a sound after 0.1 seconds of Asdrah, the object which is not only an echo of his voice is a duck)


And said the student, sir What will happen if the Earth stopped rotating suddenly? What happens

Said Professor / something serious happens there will be no houses or trees or the life on Earth because of inertia will cast them away from that surface and fly at speeds of the bullet on the line tangent to the Earth's surface and then fall down and shatter



Well ... What's her decision: - gravity

It is known that the deeper wells do not extend into the ground Elyokther of 7.5 km, but let's say that there is a well extends along the axis of the earth, from pole to another (half the diameter of the Earth 6400 km) and that someone has fallen into this Alair, which has no decision What would happen to this person if we ignore air resistance?

Student said: It will hit the rock bottom and crumbling or settle in the center of the Earth

The teacher said no, so that when he arrived to the center, the speed of his fall had reached a very large (8 km / s), which makes standing in that Anakthomra impossible, and this means that it will continue to fall to the bottom while reducing the speed to fall gradually until it reaches to the level of the corresponding edges of the well hole, and here we must cling to the edge of the well and strong, but fell a second time and sent back to the first hole

(And so will say that, who fell in the well fell into the highest for South hemisphere and will fall upon his return to the top for the north hemisphere)

This is confirmed by the laws of mechanics such as Newton's law of universal attraction and will take the process of falling back and forth 84 minutes 24 seconds exactly

Watermelon ... Bomb: - kinetic energy

Said the teacher can hold your hand Balrsash hum emanating heard someone said that the students this is beyond the scope of reasonable because the speed of the bullet high temperature and high

Actually happened to a French pilot was flying at an altitude of 2 km, where he saw something small moving close to his face what was it only that he found that he plucked a bullet taking off! But what is the interpretation that

Teacher said that the bullet does not remain always taking off speed Primary ranging between 800 and 900 m / s, as a result of air resistance reduces the bullet from its speed gradually and at the end of landing speed to 40 m / s only and with such speed was flying the plane at the time and this is what makes the shot look like a static for the pilot Vomcnh captured easily


This question I have for all Asraaaaahh I do not know where the sky
(I mean the sky the sky where there is a Lord Almighty)

Says in the hadeeth that the Prophet (peace be upon him) asked under way: Where God
She said, in the sky. He did not deny them that

Where is heaven?

Brothers sisters / if we say that the sky at the top, this is not true.

Because the highest in the Arctic is down to the south pole and the highest for the south pole is down for the Arctic and the highest for the equator is the horizontal direction for the North and South poles)

Where if the sky?

Blue sky

Can you explain that diversity in the beautiful twilight sky at sunset and the beautiful blue color and what is part of the sky more blue, and why not be the color of the sky are all regular, and why the sky is not blue at night?
Based set color of the sky on the relationship between the wavelength of the light of the sun and Asttarth particles air according to the model of Rayleigh scattering dispersion works as the electric field of the light falling on the fluctuation of electrons in molecules, which restores thus radiating light, Vtnhrv wavelengths short or end the blue of the spectrum visible for direction the original by more than deviate by wavelengths long or red end, and so Tkzn the sky above the viewer blue for the most part, when the sun is close to the more appropriate and less blue parts of the sky, which increases the distance from the sun on the 90 degree, because the sunlight that illuminates these parts from the sky, it would go a long path through the atmosphere Vinvd so some of what it contains of the blue light The sky near the sun and is on the horizon appears as a red or yellow light that Biiha go long distances through the atmosphere Vinvd blue.

Different experiments with electricity

Battery of potatoes:
Ogrz piece of copper wire and a piece of zinc (zinc) in the normal raw potato, and now I took a normal telephone handset and made the ends of the wire is located where the two pieces of wire Elamsan Almgruztin in potatoes I heard a clunk to clear when a contact. 

Explanation: This is the sound caused by the presence of an electric current holds in a grain of potatoes, just as occurs in the battery is weak at small private and Nall that the impact of chemically juice or liquid grain of potatoes on each of the two wires, causing Almadnyin for electrical energy and this process is called process galvanizing or plating elements electrically.
Stream of metal:
Take a piece of metal currency (the currency of the cash, for example) of copper metal and pieces as well as the occasion of zinc metal and then cut pieces of blotting paper soaked with salt water and arranged the pieces of copper and zinc and cut blotting paper between two pieces so that it is different and so you get the electrical energy .
And shows us that if we take a wire copper high and the Venah on the compass (50 laps almost) and we take the first party of it to touch a piece of zinc at the top and the second party to come in contact with a piece of copper in the bottom note moves a needle compass indicates the presence of an electric current in the wire under the influence of liquid salt and minerals from the passage of electric current is produced at both ends of the wire.
Does the effect of a magnetic current:
Take a wire in a high transmission of electricity and install it on a base cup glass by adhesive tape so that a curve or arc and put under the bow compass, and now move the cup so that the compass needle parallel to the arch wire completely, if reached end of the wire metal battery dry, you notice immediately move the needle Status of the compass to become orthogonal to the previous situation.
Explanation: When the passage of electric current in the wire magnetic force be formed by the arc pole magnetically south Koreans and other produce movement of the compass of the existence of the field (field) magnetic source voltage.

Electromagnet:
Wrap copper wire and insulated high-length (1 or 2 m) on the axis of iron (a nail) and then brought the poles of a battery cable and then notes that the axis attracts iron objects Aden and the reason is that the passage of electric current in the wire, especially around the axis results in the field of magnetic axis gain property made up the pole magnetization and other south Koreans If the axis of the light-iron quality, the magnetization of it quickly disappear as soon as power cuts, but if the axle is made of steel, the magnetization remains, despite the power cuts.
Graphite carrier:
Take a pen Rsasia and proven in the heel bulb small and brought the head of a pin Baktab battery and then brought a pair of scissors and brought the tip of the first body bulb metal and the other end of the scissors Baktab Battery II, and then the light bulb where it passes electricity through coal graphite to the bulb, causing lit as graphite material is good for Electricity Transmission If you painted on a sheet of ordinary writing pencil line heavy graffiti, this line transmits power Alkahrbaúakonh wire and can be verified using the handset
Mini radio:
Take the matchbox is empty (the tray containing the rods only), Enter the rods of the pencil so that Tkonan parallel rod and place the last images of a small cross over them and then brought the first penis penis Baktab battery and the second telephone handset and the other side of the handset battery Baktab second, And now if you put the handset in a room far away and then spoke in a matchbox to hear your words in the speaker.
Interpretation: that the sound vibrations affect the movement of the penis that connects the current cross-frequencies and vibration frequencies commensurate with the vibrations of speech and thus become similar to the words in the headset amplifier.
Forms of the magnetic field:
Place a piece of cardboard (cardboard) and passed the midpoint of copper wire and place the dish in question Cups identical horizontally using for example a battery arrived ends of the wire on top and sprinkle iron filings paper Vengdaa circles have formed strange and beautiful overlapping its hole, through which the wire.

Second, static electricity:

Electrified balloon:
Blow air and several Bualen Link Vohtha tightly and then Bdekha piece of woolen cloth, and its proximity to the angle of the roof of the room notes that they remain in place for a long time, as if stuck. And the reason that when the balloons let alone a piece of wool shipments are gaining power and this means that the balloons have got a negative electrical charge of a piece of wool, these shipments are called electrons and the survival of the balloons in the corner of the roof of the room is the meeting due to pending negative electrons from the positive proton in balloons ceiling of the room and that will attract negative electrons. and electrons in the ceiling of the room in which to roam electron Te and be equally balanced and the roof is bad or poor electrical conductivity for several hours when the room air dry.
Attraction and repulsion:
Blow balloons and close the mouth of two antennas each thread, and then let you Albalonen piece of woolen cloth and hold the parties to the linear Albalonen notes as they may be moved apart from each other instead of to each other as they approached, as expected. Because of Scrubs gained Alballonan negative electrons from the cloth mystic who became containing electrons and positive for this Alballonan may find that apart from each other to the clear winners for two shipments, while similar, we find that close to the balloons and are attracted to the mystic cloth that contains positive protons and thus
Curvature of the path of water flow:
Take a plastic spoon and Adekha several times on a piece of woolen cloth and then open the faucet until the water a little bit of water percolated Silana lightly and try not to approach the plastic spoon is Dekha As mentioned flume water immediately how to bend notes Ceylon and water tends to near the spoon. Vaahnat power gained by the spoon as a result Scrubs affected the water molecules and caused the attraction towards her. And if it reaches the water flow to the spoon was liberated shipments immediately and faded away and returned to the water flow vertically as normal rainfall and the reason for this is that the appointments, a spoon of water shipments gained.
Sort salt pepper ground:
Mix a little bit of salt is ground fine with a little pepper soft. How can we work to sort pepper for salt?
Take a teaspoon of plastic commonly used in food and Adekha on a piece of wool and put the spoon over the mixture Madaukh notes immediately jumped high and pepper to stick a spoon. The reason for this is that Scrubs earn Almlqh electrical discharges lead to the mixture to attract a spoon. And if you put a spoon just enough of the mixture is close to notice that the pepper is soft, which is attracted to the spoon because it is lighter than salt and salt if you wish to attract Aiza you have to do that closer to the spoon of the mixture even more.
Ketroscop is simple:
Take an empty bottle and lid Skewer and enter the middle of this hole in the copper rod Mtauajja in the form of hook and tightened plug the hole, through which a rod or wire are well separated by an insulator for the wire cover and dismiss him with him and commented on the hook thin rectangular plate of metal from the aluminum bent in the middle of the symmetric. And now charge the pen with plastic wrap Bdekh on Canvas Sophie Deka well to acquire electrical charges sufficient and if not possible you have a pen used plastic comb, or the like and near the pen of the head of the penis or wire notes on the spot spacing sections of plate aluminum from each other When touching the pen to the wire by moving electrons through the wire to the aluminum sections, where tin is shipped Ksmiha equally leading to the spacing sections from each other depending on the strength of shipments enjoyed by the pen

Third, experiments in the magnetization:

Htoot magnetic force:
Take a paper print A4 for example, and placed on the magnet in the form of U and then brought refinery small soft and place in which filings iron soft and Ankhalha evenly over the paper with shaken lightly and you will see then a mirror image of the magnet and lines around atoms of iron filings, which are settled according to the paths magnetization and events that show you the beautiful lines of a consistent
In order to substantiate this view, but experience has prepared a paper marked with the wax melted, and after that the lines of iron filings near the iron garrison of which even begins to melt the wax and then let it cool until you have an image consists of a beautiful way and help to explain.

Pencil Mobile:
Take a pen and polygon Rsasia put on the table then take the rarely last long circular section and has focused Maamda pen first and then near the top of the pen notes how good a magnet is attracted to the pencil magnet
Because the graphite inside the pencil has the viability of magnetization but it does not enjoy the same advantages enjoyed by the iron in its ability to magnetize.
Inclination toward the pole:
Take Dbusan Fullavean Ojolhma Mmagntin great and good, then take a piece of sponge and a length of industrial display pen to write about and then passed a piece of the middle of a needle in a balanced way and put this piece of the balance between the two glasses and the direction of Mark (s) in the same direction South North notes that the piece tends to the North and the angle of inclination varies from country to country and from place to place and in the region of the Earth's magnetic pole is the direction of the magnetic needle vertically.
Ducks magnetic:
Cut a piece of cardboard the slave in the form of a duck in duplicate and Olsqhma with each other and Ogrz between the two versions pin magnetized and then cut another model similar to the first and put the pin similar and proved each model inside the cover of cork or a cork round and leave the two models in a dish containing notes how the water meets two models in terms of head or tail of the hand toward the north and south according to the magnetization Aldbusan
And the movement of the two models of the Ducks cause a strong and different events: the poles attract each non-equals, heterogeneous effect of the two electrodes and equals the effectiveness of terrestrial magnetism

Plasma

Plasma .....
Password plasma for most people means only that it the fourth case of material which is found only in the nuclear reactions that occur in the depths of the stars and on the roofs or those that occur in nuclear reactors, where high temperatures and high pressure, but there are many industries technological very complex completely dependent on the use of plasma processed in the laboratory, these industries from manufacturing electronic integrated circuits and manufacturing of diamonds and served chips and wires of superconducting materials for electricity and gas as well as in the conversion of toxic gases as well as useful for this study and understand the mysteries of the universe vast. In this article will shed light on the plasma and its uses.


Most of the material found in nature in three situations, the solid state and liquid state and gaseous state and can convert material from one state to another either by changing temperature or pressure, and in all these cases, the atoms of the material retains electrons associated with the electrical forces of attraction. But there is a fourth case of a substance to be the image of gas but this gas contains a mixture of equal numbers of positively charged ions and electrons is negative. This mixture is called the gas ionized or plasma Plasma, and as the plasma unstable state, the power of attraction electrical work to restore the Union of positive and negative charges with each other, and the result of re-union is launching light of a specific frequency depends on the energy levels of atoms making up the material plasma.



Where are the plasma?

Often most of the material found in this vast universe there is in the form of plasma. This plasma is at high temperatures and high density as well, and change these conditions from one place to another, for example, temperature of center of the sun ten million degrees Celsius while on the surface, the temperature of up to six thousand degrees Celsius, hence, the plasma inside the sun quite different from the outside. But on the globe where there is often material in the solid state, and the layers of the atmosphere is a gas is ionized, ie that there is no case of normal plasma on the surface of the earth. But you can work in a laboratory plasma? If you read this article under the light of fluorescent lamp (neon), the source of this light is a plasma manufacturer, when the passage of power supply in the gas (gas mercury) under low pressure, it works on the ionization of the gas, leaving a mixture of positive ions and electrons, which will quickly be combine with each other and the result is emission of bright light, and continue these processes (ionization and the European Union) as long as the power supply in the force. This is an example on the source plasma temperature is low in your home.

But the past and the present day astrophysicists interested in to reveal the secrets of the universe and understand what is happening on the surface of the sun and other stars. So scientists tried to manufacture the same stars found in the plasma in the laboratory, and to make this plasma scientists have developed various devices capable of generating tremendous energy to produce the plasma in the same plasma conditions found in nature, was one of these devices is a device specifically magnetic Magnitec-confinment devices. And has to know a lot of information on the composition of the surface and understand the outside of the solar envelope. But what about the plasma inside the sun with very high temperatures. How can be manufactured in the laboratory?

In fact, until recently, and the development of laser Ajhrh became possible to get a plasma similar to those found on any star, whether inside or outside of it.



Get a plasma by laser?

We know that light is a fluctuation of two perpendicular, one electric and one magnetic. The laser is just a light has distinctive characteristics make the radiance intensity (energy per unit area per unit time) increases with increasing electric field and magnetic Mujath.



But you can have a light output of the laser is stronger than solid objects? The intensity of the electric field of the laser beam of 5x1011v / m when the intensity of radiance 3x1020W/m2, and in these days reach the intensity of some types of laser radiation to approximately 1022W/m2. Compared to radiation strongly regular electric lamp (60Watt) at a distance of two meters or meter is not more than 0.1W/m2. Since the electric field of this radiation much greater than the electric field that connects the atoms of solids to each other and thus the electric field of the laser beam will affect the electrons solids separated from the atoms, leaving the positive ions and thus prevents the laser part of the solid material to the case of plasma. It is clear from the foregoing that the use of lasers can be focused to produce a plasma at very high temperatures inside the laboratory and at low cost. Figure (1) how to make plasma in the laboratory using a laser.

This system has many important applications in the field of astrophysics where the choice of target material and design engineering are given so that the plasma generated in the laboratory plasma conditions similar to the real star to be studied. In addition to that, the plasma used in many industries.



Industrial applications of plasma

Integrated circuit industry

Using plasma with low temperatures in many important areas, for example, most integrated circuits very complex and entering in the composition of each electronic device, this circuit contains tens of thousands of transistors and capacitors connected to each other by wire diameter in the range 0.1 micrometers, this type of nanotechnology and manufactured using a complex Albularma, where the plasma carve electronic circuits on a chip based on silicon metal mask is subject to the slide.

In this process is a sculpture on a silicon chip as follows: -

Since the electrons within the plasma free movement and energy higher than the cation, they reach the outskirts of the plasma quickly and in turn attract cations direction and Tjlha towards the slide and when the collision cation areas exposed on the slide you Bnanha, and then replaces the mask metal the last printed by the circuit of class II Thus for the third and fourth layer ...... And so on until the process of sculpture.

There is another way which is followed depends on the use of composite Carbon tetrafluoride CF4 plasma as a source of production, and then turns this compound to other parts of fluorine atoms. These atoms react with silicon atoms, consisting of the slide and be a new compound is a Silicon tetrafluoride, which can be removed during the pumping process. Clear from the foregoing that this method is the chemical process in which the fluorine atoms devour silicon to be removed. This process is faster than the previously mentioned process of sculpture.

It should be noted that research and development underway since 1980 and until now to get the plasma regularly to cover the largest possible area where the chip silicon used an old 2 per cm 2 now they are up to 20 cm 2, and this plasma has many uses, they are used in computer screens of mobile Notebook computer as a source Optical, which led to a major development in the field of display technology. Scientists are now seeking to get the screen area of ​​1 square meter and thickness of no more than 4-5 cm to be used as a screen TV can be suspended in homes and shops, without running into the room, and this will be achieved to reach a homogeneous plasma on an area of ​​1 meter square.



Portfolio of a clean environment

Plasma is used now in many developed countries to get rid of toxic substances polluting the environment, based on the chemical processes that are unique within the plasma. Where the plasma can convert toxic substances emitted from factory chimneys and car exhaust gas such as sulfur dioxide (SO) and nitric oxide (NO) to non-toxic materials. For example, NO gas before it comes out of the chimney to the atmosphere, draws upon a package of high-energy electrons from a device installed in the middle of the chimney works to ionize gases (NO toxic material and air) any transformation to the case of plasma. Before going out to be the air ionization phase has ended and is composed of nitrogen and oxygen molecules as a result of re-union. Thus, we have around us polluting gases into gases and low-cost beneficial.

It should be noted here that it was going to address the newly released gases from the exhausts of cars, where the device was installed in the plasma exhaust to the car addresses the toxic gases into the atmosphere before they leave.

Also conducted numerous experiments on solid waste and liquid plasma are used at high temperatures up to 6000 ° C working to vaporize and break down toxic substances and converts them to non-toxic gases, and in the end of the process that remains of the solids in the form of glass. It was in America last year to get rid of about 4000 warehouse containing solid waste and polluting the environment by the plasma. This has been a waste buried in the ground, which were causing the dangers of pollution. Using the plasma can now get rid of 200 kilograms of toxic materials in time.



How to create a plasma in the laboratory

In order to make a plasma under low pressure to a gas, all that is needed is a vicious air meter and display half a meter almost as well as a source of nutrition for the AC, (in the industry be a source of power in the field of radio frequency 13.56MHz and newly can use the devices microwave frequencies higher 2.45 GHz). In the plasma can actually work in any form, but the most widely used in industry is shown in Figure (2), and contains two tablets half Qtarhama metal about 15 centimeters and the distance between them of 4-5 cm. After pumping the air by the gas enters the circle to be converted to a state plasma may be a mixture of gases, and once the passage of electric current (~ 200Watt) begins with a source of gas in the glow a bright light in color depends on the type of gas.

Definitions in Physics

Momentum: the amount of physical direction is heading in the same direction and speed of the body expressed as body mass Bhasal hit in speed.
* Strengths: time rate of change in the amount of movement.
* Payment: is the amount of bound equal to the product of the force acting at the time of impact.

* Average thrust: the force is fixed in the body if affected during the same period of time that affect the changing power earned him the same amount of pay.
* Theory of payment - the amount of move: You will pay caused by power collected in the body during a period of time equal to the change in the amount of body movement during that period.
* System: a set of particles that affect each other in some.
* Closed or isolated system: a set of objects that remain constant throughout the mass of any operation, and the only forces that affect the closed system isolated are the forces exchanged between the objects or particles within the system.
* Body Gassae: is the body that do not change the dimensions of engineering at the points where the impact of forces such as: metal balls.
* Body is Gassae: is the body that change the dimensions of engineering at the points where the impact of forces such as a piece of wet dough.
* Center of mass: a set of objects that can be replaced by a bullet body mass equal to the total mass of objects and the subject in the center of mass collection of objects in the system.
* The text of the law of conservation of momentum: "If the outcome of the external forces affecting the collection of objects, including a reciprocal effect in a closed system = zero, the total amount of movement of these objects remains constant amount and direction before and after the mutual influence."
* Collision: the impact of exchange between two objects, one or more mobile so that at least a temporary reaction is between him and the other the body through the exchange of impact forces pay as Newton's third law, which occurs during a very short period.
* The time of the collision: the time of the impact of the forces exchanged between the colliding objects.
* Collision flexible: the collision, which is the kinetic energy of the college and also the amount of move reserved, meaning that there is no loss in kinetic energy of the system as the amount of before and after the collision is fixed and separated objects ceased immediately after the collision without that happening to them any change in shape and temperature Example : The collisions between atomic particles collisions flexible.
* Inelastic collision: A collision in which the amount of reservation and the reservation to move the energy of movement, where the proportion of the kinetic energy lost a very large and the objects ceased to unite together Almtsadman Akunan any one body after the collision.
* Relative speed: the speed at which one of them seems to be moving in when the body is made of the relative speed with the other two cars traveling the same speed and in the same direction is equal to zero.
* Regression coefficient: the ratio between the vertical speed of the vehicle relative to the two objects after the collision to the vehicle speed relative to the vertical of the two objects before the collision.
* Conductive materials: The materials that contain free shipments.
* Current terminology: has come to represent the direction of electric current in the circuit towards the movement of positive charges is contrary to the actual direction of movement of electrons in metallic conductors, which is called stream-mail.
* Current density: the result of dividing the intensity of electric current on-sectional area of ​​Mosul, the intensity of electric current density is measured in unit w 1 A / m 2.
* Ohm's law: the intensity of the power density of direct proportion to the intensity of the electric field inside the moving metallic conductors and symbolized by the

 "W = T / A"
     
* Electrical resistance: the reluctance expressed by the connector for the passage of the current resistance of Mosul.
* Resistivity: conductor resistance of a length of 1 m and cross section area of ​​cross 13 o'clock ².
* Connectors with a linear resistance (ohmic) conductors that are applied by the law of Ohm.

The great graphene name game

By Tushna Commissariat

Here at Physics World, the word graphene gets used a lot. You might find that simply saying the word “graphene” elicits a groan from most of the editorial team. But this is usually followed quite swiftly by a fair amount of interest, because it’s undeniable that graphene is some kind of “wonder material” with a seemingly endless list of bizarre properties and applications. Along with the plethora of potential applications for graphene comes an interesting array of names for graphene-based materials. When our news editor Michael Banks heard that scientists in Spain had created an acoustic analogue for graphene, he dubbed it “graphone” – a name that has a certain resonance to it!

But it seems that researchers at the UK’s University of Exeter really ran out of suitable graphene-related names recently as they have decided to call their new graphene-based material “GraphExeter”. According to the researchers, GraphExeter is the most transparent, lightweight and flexible version of graphene that is also an excellent at conducting electricity, and so “could revolutionize the creation of wearable electronic devices, such as clothing containing computers, phones and MP3 players”.

The researchers created GraphExeter by sandwiching molecules of ferric chloride between two layers of graphene. Ferric chloride enhances the electrical conductivity of graphene without affecting the material’s transparency. The researchers say it is also much more flexible than indium tin oxide (ITO), the main conductive material currently used in electronics. As ITO is used so extensively, it is expensive and resources are expected to run out by 2017. The research is published in the journal Advanced Materials here.

Lead researcher Monica Craciun says “GraphExeter could revolutionize the electronics industry. It outperforms any other carbon-based transparent conductor used in electronics and could be used for a range of applications, from solar panels to ‘smart’ T-shirts. We are very excited about the potential of this material and look forward to seeing where it can take the electronics industry in the future.”

According to a University of Exeter press release, the researchers are “now developing a spray-on version of GraphExeter, which could be applied straight onto fabrics, mirrors and windows”. While the applications of GraphExeter may be varied and interesting, the researchers might have to come up with a slightly more user-friendly name for their new material if they intend to use it in a T-shirt venture!

Boomerang in Zero Gravity

Boomerang in Zero Gravity
Japanese astronaut Takao Doi proves that a boomerang will always return to the person who threw it — even in outer space.

How to hide from a magnetic field

Researchers in Europe have built a magnetic cloak that, in theory, is reasonably practical to manufacture. An object concealed by the new cloak, the researchers claim, is magnetically undetectable, while the cloak itself is made from materials available in many physics labs the world over. This means that it is, in principle, the first cloak that should be reasonably practical to manufacture. 

Cloaks and shields

In 2011 Alvaro Sanchez and colleagues at Universitat Autònoma de Barcelona, Spain, developed a theory for a type of magnetic cloak they called an "antimagnet" that would have two crucial properties. One is that any magnetic field created within the cloak would not leak outside the cloaked region and the other is that the cloak and the cloaked region would be undetectable by an external magnetic field; that is, the field would not be distorted by the cloak. Now, Sanchez along with Fedor Gömöry and colleagues from the Slovak Academy of Sciences, has designed and demonstrated a modified version of the cloak proposed last year.

The new cloak is a simple bi-layer cloak made up of two common materials – an inner superconducting layer made up of a high-temperature superconducting tape and an outer ferromagnetic layer composed of a few turns of a thick FeNiCr commercial alloy sheet. "The cloak we proposed last year was more of an ideal cloak," explains Sanchez. "But it was complicated with 10 layers and included superconducting plates. This new cloak, while not perfect, is a much simpler design for achieving similar results using a static uniform magnetic field." He adds that it is fair to say that this is the first cloak that is an exact cloak that can be feasibly implemented in practice.

The superconducting layer on its own repels the magnetic field, while a ferromagnetic layer on its own attracts the magnetic field lines; so both independent layers distort the field. The cloak is the accurate combination of the two layers, determined by a specific radius, which adjusts for the permittivity (μ) such that there is no external field distortion at all. This radius is calculated using Maxwell equations. "It is quite amazing that almost 160 years after Maxwell equations were first developed, we are still finding new solutions based solely on them!" says Sanchez.

Perfection problems

Sanchez tells physicsworld.com that the entire team is highly inspired by the initial work on building invisibility cloaks using transformation optics carried out by John Pendry and colleagues at Imperial College London since 2006. "There are generally two ways of achieving a cloak – either using transformation optics or using plasmonics. The problem with the first is that, while it is theoretically the perfect cloak, it is nearly impossible to physically create. With plasmonics, while the materials are available, you get a slight shadowing or scattering effect, not a complete cloak at all. This is the first time that you get both using commercially viable materials," Sanchez explains.

Sanchez points out that an advantage in developing a cloak for a static magnetic field is that, for such a field, the magnetic and electric effects decouple and the researchers only have to consider the magnetic permeability. The team tested its cloak using a static field of 40 mT – which is greater than the Earth's magnetic field. Currently, the cloak has been built on a small but reasonable scale – 12.5 × 12 mm. Sanchez explains that another advantage is that, for a static magnetic field, the cloak can work on any length scale – from microns to metres – as there is no intrinsic cut-off, unlike other cloaks that work at fixed wavelengths.

Because the cloak is capable of running under relatively strong magnetic fields and relatively warm liquid-nitrogen temperatures, and as it is made from commercially available materials, it could be readily put to practical use, the researchers say. The team is also looking at other methods to manipulate and control magnetic fields into different "shapes", for purposes other than cloaking, in the coming months.

The research is published in Science 335 1466.

About the author

Tushna Commissariat is a reporter for physicsworld.com

Quirky solar cell sets new efficiency record

Researchers in the US have built a new type of solar cell that emits light as well as absorbs it, making it the most efficient single-junction device ever developed. The efficiency of their prototype cell allows it to convert 28.6% of the Sun's energy into electricity. This is a considerable increase from the previously recorded highest efficiency of 26.4%, which was achieved in 2010.

Scientists have known since 1961 that the absolute limit for the amount of energy that can be harvested from sunlight hitting a typical solar cell is about 33.5%. However, for almost five decades researchers have been unable to come close to achieving this theoretical efficiency. But now, Eli Yablonovitch and his graduate student Owen Miller from the University of California, Berkeley have designed and built a new type of solar cell that gets closer to that limit by mimicking the behaviour of a light-emitting diode. That is to the say the solar cell is highly capable of absorbing light as well as emitting it. In fact, it is the controlled emission of light that has boosted the efficiency.

The researchers have shown that the better a solar cell is at emitting photons, the higher its voltage is and the greater its efficiency. "[The result] is almost paradoxical and counterintuitive. It can be quite confusing to grasp at first," says Yablonovitch, as he tells physicsworld.com that he and his colleagues discovered the connection while trying to resolve the large gap between the theoretical and achieved limits for solar-cell efficiency.

Managing photons

The solution lay in a mathematical connection between absorption and emission of light – a phenomenon better understood as "photon management". Conventionally, photon management involves controlling the photons incident on a solar cell so that a photon ejects as many electrons as possible, thereby generating the maximum amount of electric current. "But there is another aspect to photon management, in that we manage not only the incident light, but also the emitted light. Emitted photons sometimes get 'lost' within the cell, so what we do is make sure those photons are emitted," explains Yablonovitch. In a conventional solar cell, photons from the Sun hit a semiconductor material, knocking electrons loose and allowing them to flow freely. But this process can also generate new photons, in a process known as "luminescent emission". As there is a fundamental thermodynamic link between absorption and emission, designing solar cells to emit light causes an increase in the voltage produced by the device.

The researchers' novel concept has been put into practice by a company called Alta Devices, which was co-founded by Yablonovitch and California Institute of Technology physicist Harry Atwater in 2007. The firm was set up specifically to produce economic and high-energy solar cells. The new prototype solar cell is made of gallium arsenide, a material often used to make solar cells for satellites. The result is a device that operates at 28.6% efficiency.

First to put into practice

The prototype solar cell

While the theory of luminescent emission causing an increase in voltage has been known for a while, it has never been put into practice. "It is somewhat puzzling why it has never been used in the field of solar-cell development until now. But a lack of certain requirements might explain that," says Yablonovitch. He goes on to say that solar cells are "grown" on substrates that are generally of poor quality and act as "sinks" for the emitted luminescent photons, which are then lost. The new cell made by Alta Devices is separated from the substrate, which delivers a much better performance. "In fact, we separate the substrates on which the cells are grown and then re-use them. This not only helps with efficiency, but it also brings the cost of producing our cells down, and so it is a key factor," says Yablonovitch. He explains that the cells are still as thin (1 µm) as traditional cells and so people are genuinely shocked to know the devices have been developed cheaply using gallium arsenide. Alta Devices is already producing the cells on an industrial scale, with samples being shipped to customers.

Yablonovitch says he hopes researchers will be able to use this technique to achieve efficiencies close to 30% in the coming years. And given that the work applies to all types of solar cells, the findings have implications throughout the field.

The team will present its findings at the Conference on Lasers and Electro Optics to be held in early May in California in the US.

The research is to be published in Journal of Photovoltaics.

'Missing silicon problem' solved, say geophysicists

Researchers in Japan have new evidence that the Earth's lower mantle contains more silicon than its upper mantle. The results suggest that the composition of the Earth's silicates match the type of meteorites thought to exist in the solar nebula from which the Earth was created.

The Earth's mantle can be divided into three sections: the upper mantle, which stretches from the thin crust down to about 400 km in depth; a transition zone of about 250 km; and finally the lower mantle, which stretches from the transition zone to about 2900 km in depth. Most geoscientists agree that the upper mantle is composed mostly of peridotite, a dense igneous rock containing a high proportion of the mineral olivine (Mg,Fe)₂SiO₄. At the transition zone, a change in the way seismic waves propagate has generally been explained by a phase transition in the structure of the olivine, suggesting that the lower mantle, too, is peridotite in composition. If this is true, however, the Earth would contain far less silicon than chondritic meteorites – the type of meteorites thought to exist at the time of the Earth's formation.

More or less silicon?

In the past, this "missing silicon problem" has provoked much debate. Some geoscientists believe that the missing silicon must be made up in the Earth's core, while others believe the lower mantle must contain an additional source of silicon. There has even been a suggestion that the meteorites from which the Earth formed contained less silicon than is generally assumed.

Now, geophysicist Motohiko Murakami of Tohoku University in Sendai and colleagues claim to have solved the missing silicon problem. They believe that the lower mantle in fact contains more silicon than the upper mantle – which is consistent with the Earth having been formed from chondritic meteorites. "The main result of our work is that the mantle has [a] chemically stratified structure with [a] silicon-enriched lower mantle in comparison with the upper mantle," says Murakami.

Murakami and colleagues performed laboratory-based seismic-velocity measurements on two possible lower-mantel minerals – silicate perovskite, or (Mg Fe)SiO₃, and ferropericlase, or (Mg,Fe)O – under very high pressures and temperatures. Comparing these measurements with actual seismic-velocity data using a model, the researchers found that more than 93% of the lower mantle should be made of perovskite, the silicon-rich mineral.

James Connolly, a geoscientist at the Swiss Federal Institute of Technology in Zurich, says that in recent years there has been a trend in seismic models towards a silicon-enriched lower mantle, although he adds that the enrichment proposed by Murakami and colleagues is the "most extreme" he has seen. He thinks the group's conclusions are interesting because they support the notion that the mantle has two separate layers that circulate independently, and that the Earth was formed by accretion of chondritic meteorites. "The popularity of both of these hypotheses has been waning in recent years," he says.

Some uncertainty

However, geophysicist Baosheng Li of Stony Brook University in New York thinks there may be a problem with the Japanese researchers’ modelling. For example, he says that there is a "large uncertainty" in their temperature measurements, which may compromise their conclusions. Still, he thinks the group’s techniques are, in general, "first class". "I found this paper interesting, although in my personal view it still needs more data to confirm [that] the lower mantle holds the 'missing silicon'," he adds.

The research is described in Nature.