A solar cell is a device for converting energy from the sun into electricity.
The high-efficiency solar cells you can buy at Radio Shack and other stores are made from highly processed silicon, and require huge factories, high temperatures, vacuum equipment, and lots of money.
If we are willing to sacrifice efficiency for the ability to make our own solar cells in the kitchen out of materials from the neighborhood hardware store, we can demonstrate a working solar cell in about an hour.
Our solar cell is made from cuprous oxide instead of silicon. Cuprous oxide is one of the first materials known to display the photoelectric effect, in which light causes electricity to flow in a material.
Thinking about how to explain the photoelectric effect is what led Albert Einstein to the Nobel prize for physics, and to the theory of relativity.
Materials you will need
The solar cell is made from these materials:
A sheet of copper flashing from the hardware store. This normally costs about $5.00 per square foot. We will need about half a square foot.
Two alligator clip leads.
A sensitive micro-ammeter that can read currents between 10 and 50 microamperes. Radio Shack sells small LCD multimeters that will do, but I used a small surplus meter with a needle.
An electric stove. My kitchen stove is gas, so I bought a small one-burner electric hotplate for about $25. The little 700 watt burners probably won't work -- mine is 1100 watts, so the burner gets red hot.
A large clear plastic bottle off of which you can cut the top. I used a 2 liter spring water bottle. A large mouth glass jar will also work.
Table salt. We will want a couple tablespoons of salt.
Tap water.
Sand paper or a wire brush on an electric drill.
Sheet metal shears for cutting the copper sheet.
How to build the solar cell
My burner looks like this:
The first step is to cut a piece of the copper sheeting that is about the size of the burner on the stove. Wash your hands so they don't have any grease or oil on them. Then wash the copper sheet with soap or cleanser to get any oil or grease off of it. Use the sandpaper or wire brush to thoroughly clean the copper sheeting, so that any sulphide or other light corrosion is removed.
Next, place the cleaned and dried copper sheet on the burner and turn the burner to its highest setting.
As the copper starts to heat up, you will see beautiful oxidation patterns begin to form. Oranges, purples, and reds will cover the copper.
As the copper gets hotter, the colors are replaced with a black coating of cupric oxide. This is not the oxide we want, but it will flake off later, showing the reds, oranges, pinks, and purples of the cuprous oxide layer underneath.
The last bits of color disappear as the burner starts to glow red.
When the burner is glowing red-hot, the sheet of copper will be coated with a black cupric oxide coat. Let it cook for a half an hour, so the black coating will be thick. This is important, since a thick coating will flake off nicely, while a thin coat will stay stuck to the copper.
After the half hour of cooking, turn off the burner. Leave the hot copper on the burner to cool slowly. If you cool it too quickly, the black oxide will stay stuck to the copper.
As the copper cools, it shrinks. The black cupric oxide also shrinks. But they shrink at different rates, which makes the black cupric oxide flake off.
The little black flakes pop off the copper with enough force to make them fly a few inches. This means a little more cleaning effort around the stove, but it is fun to watch.
When the copper has cooled to room temperature (this takes about 20 minutes), most of the black oxide will be gone. A light scrubbing with your hands under running water will remove most of the small bits. Resist the temptation to remove all of the black spots by hard scrubbing or by flexing the soft copper. This might damage the delicate red cuprous oxide layer we need to make to solar cell work.
The rest of the assembly is very simple and quick.
Cut another sheet of copper about the same size as the first one. Bend both pieces gently, so they will fit into the plastic bottle or jar without touching one another. The cuprous oxide coating that was facing up on the burner is usually the best side to face outwards in the jar, because it has the smoothest, cleanest surface.
Attach the two alligator clip leads, one to the new copper plate, and one to the cuprous oxide coated plate. Connect the lead from the clean copper plate to the positive terminal of the meter. Connect the lead from the cuprous oxide plate to the negative terminal of the meter.
Now mix a couple tablespoons of salt into some hot tap water. Stir the saltwater until all the salt is dissolved. Then carefully pour the saltwater into the jar, being careful not to get the clip leads wet. The saltwater should not completely cover the plates -- you should leave about an inch of plate above the water, so you can move the solar cell around without getting the clip leads wet.
The photo above shows the solar cell in my shadow as I took the picture. Notice that the meter is reading about 6 microamps of current.
The solar cell is a battery, even in the dark, and will usually show a few microamps of current.
The above photo shows the solar cell in the sunshine. Notice that the meter has jumped up to about 33 microamps of current. Sometimes it will go over 50 microamps, swinging the needle all the way over to the right.
How does it do that?
Cuprous oxide is a type of material called a semiconductor. A semiconductor is in between a conductor, where electricity can flow freely, and an insulator, where electrons are bound tightly to their atoms and do not flow freely.
In a semiconductor, there is a gap, called a bandgap between the electrons that are bound tightly to the atom, and the electrons that are farther from the atom, which can move freely and conduct electricity.
Electrons cannot stay inside the bandgap. An electron cannot gain just a little bit of energy and move away from the atom's nucleus into the bandgap. An electron must gain enough energy to move farther away from the nucleus, outside of the bandgap.
Similarly, an electron outside the bandgap cannot lose a little bit of energy and fall just a little bit closer to the nucleus. It must lose enough energy to fall past the bandgap into the area where electrons are allowed.
When sunlight hits the electrons in the cuprous oxide, some of the electrons gain enough energy from the sunlight to jump past the bandgap and become free to conduct electricity.
The free electrons move into the saltwater, then into the clean copper plate, into the wire, through the meter, and back to the cuprous oxide plate.
As the electrons move through the meter, they perform the work needed to move the needle. When a shadow falls on the solar cell, fewer electrons move through the meter, and the needle dips back down.
A note about power
The cell produces 50 microamps at 0.25 volts.
This is 0.0000125 watts (12.5 microwatts).
Don't expect to light light bulbs or charge batteries with this device. It can be used as a light detector or light meter, but it would take acres of them to power your house.
The 0.0000125 watts (12.5 microwatts) is for a 0.01 square meter cell, or 1.25 milliwatts per square meter. To light a 100 watt light bulb, it would take 80 square meters of cuprous oxide for the sunlit side, and 80 square meters of copper for the dark electrode. To run a 1,000 watt stove, you would need 800 square meters of cuprous oxide, and another 800 square meters of plain copper, or 1,600 square meters all together. If this were to form the roof of a home, each home would be 30 meters long and 30 meters wide, assuming all they needed electricity for was one stove.
There are 17,222 square feet in 1,600 square meters. If copper sheeting costs $5 per square foot, the copper alone would cost $86,110.00 USD. Making it one tenth the thickness can bring this down to $8,611.00. Since you are buying in bulk, you might get it for half that, or about $4,300.00.
If you used silicon solar panels costing $4 per watt, you could run the same stove for $4,000.00. But the panels would only be about 10 square meters.
Or, for about a dollar, you can build a solar stove out of aluminum foil and cardboard. For about $20, you can build a very nice polished aluminum parabolic solar cooker.
Infosys Technologies Ltd. (NASDAQ: INFY) was started in 1981 by seven people with US$ 250. Today, we are a global leader in the "next generation" of IT and consulting with revenues of over US$ 4 billion.
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Infosys has a global footprint with over 50 offices and development centers in India, China, Australia, the Czech Republic, Poland, the UK, Canada and Japan. Infosys and its subsidiaries have 105,453 employees as on September 30, 2009
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1. The word "queue" is the only word in the English language that is still pronounced the same way when the last four letters are removed.
2. Beetles taste like apples, wasps like pine nuts, and worms like fried bacon.
Of all the words in the English language, the word 'set' has the most definitions!
3. What is called a "French kiss" in the English speaking world is known as an "English kiss" in France.
4. Almost" is the longest word in the English language with all the letters in alphabetical order.
5. Rhythm" is the longest English word without a vowel.
6. In 1386, a pig in France was executed by public hanging for the murder of a child
7. A cockroach can live several weeks with its head cut off!
8. Human thigh bones are stronger than concrete.
9. You can't kill yourself by holding your breath
10. There is a city called Rome on every continent.
11. It's against the law to have a pet dog in Iceland!
12. Your heart beats over 100,000 times a day!
13. Horatio Nelson, one of England's most illustrious admirals was throughout his life, never able to find a cure for his sea-sickness.
14. The skeleton of Jeremy Bentham is present at all important meetings of the University of London
15. Right handed people live, on average, nine years longer than left-handed people
16. Your ribs move about 5 million times a year, everytime you breathe!
17. The elephant is the only mammal that can't jump!
18. One quarter of the bones in your body, are in your feet!
19. Like fingerprints, everyone's tongue print is different!
20. The first known transfusion of blood was performed as early as 1667, when Jean-Baptiste, transfused two pints of blood from a sheep to a young man
21. Fingernails grow nearly 4 times faster than toenails!
22. Most dust particles in your house are made from dead skin!
23. The present population of 5 billion plus people of the world is predicted to become 15 billion by 2080.
24. Women blink nearly twice as much as men.
25. Adolf Hitler was a vegetarian, and had only ONE testicle.
26. Honey is the only food that does not spoil. Honey found in the tombs of Egyptian pharaohs has been tasted by archaeologists and found edible.
27. Months that begin on a Sunday will always have a "Friday the 13th."
28. Coca-Cola would be green if colouring weren’t added to it.
29. On average a hedgehog's heart beats 300 times a minute.
30. More people are killed each year from bees than from snakes.
31. The average lead pencil will draw a line 35 miles long or write approximately 50,000 English words.
32. More people are allergic to cow's milk than any other food.
33. Camels have three eyelids to protect themselves from blowing sand.
34. The placement of a donkey's eyes in its' heads enables it to see all four feet at all times!
35. The six official languages of the United Nations are: English, French, Arabic, Chinese, Russian and Spanish.
36. Earth is the only planet not named after a god.
37. You're born with 300 bones, but by the time you become an adult, you only have
38. Some worms will eat themselves if they can't find any food!
39. Dolphins sleep with one eye open!
40. It is impossible to sneeze with your eyes open
41. The worlds oldest piece of chewing gum is 9000 years old!
42. The longest recorded flight of a chicken is 13 seconds
43. Queen Elizabeth I regarded herself as a paragon of cleanliness. She declared that she bathed once every three months, whether she needed it or not
44. Slugs have 4 noses.
45. Owls are the only birds who can see the colour blue.
46. A man named Charles Osborne had the hiccups for 69 years!
47. A giraffe can clean its ears with its 21-inch tongue!
48. The average person laughs 10 times a day!
49. An ostrich's eye is bigger than its brain
50. One of these facts is false, can you guess which one? Answer is below.
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The 'fact' about pet dogs in Iceland is incorrect. However, it is true that an epidemic once killed most of the Icelandic dog population
here is the list of books useful for GATE - EE ....
hope this might b usefull ....
Electrical Machines
Electrical Machinery- P.S.Bimbhra
Electrical Machines- J.B.Gupta
Electrical Machinery (5th Edition) -Fitzgerald, Charles Kingsley
Electrical Machines (2nd Edition)- E.J.Nagrath, D.P.Kothari
The Performance And Design Of Alternating Current Machine -M.G.Say
Theory Of Alternating Current -Machinery Langsdorf
Elements Of Electromagnetics (3rd Edition) -Sadiku
Problems In Electrical Engineering (4th Edition) -N.N.Parker Smith
Electrical Engineering (Problems & Solutions) -V.C.Natesan
The Performance And Design Of Direct Current Machines -A.E.Clayton, N.N.Hancock
Electromechanics - I (Direct Current Machine) -S.Kamakshaiah
Synchronous Induction And Special Machines- Sheilac Haren
Electrical Technology (Vol - II) -B.L.Dheraja, A.K.Dheraja
Power Electronics
Priniciples Of Electric Machines and Power Electronics (2nd Edition)- P.C.SEN
Thyristorised Power Controllers -Dubey, Sinha, Doradla, Joshi
Power Electronics (2nd Edition) -Rashid
Power Electronics -P.S.Bimbhra
Power Electronics (2nd Edition) -Mohan/Undeland
Power Electronics- P.C.SEN
Power Electronics (2nd Edition)- Mohan, Undeland, Robins
Power Electronics- Singh, Kanchandani
Digital And Microprocessors
Modern Digital Electronics(2nd Edition) Jain
Digital Fundamentals (3rd Edition) Floyd
Digital Electronics And Microprocessor R.P.Jain
Power Systems
Power System Stability (Vol - I) Kimbark
Power System Stability (Vol - II) Kimbark
Power System Engineering Nagrath, Kothari
Power Systems - II Y.V.Naidu
Power System Production And Switch Theorem Badri Ram, Viswakama
Modern Power System Analysis (2nd Edition) Nagrath, Kothari
Power System (Millennium Edition) V.K.Mehta
Electrical Power Systems Wadhwa
Power System Analysis Haddi, Scadat
Elements Of Power System Analysis (4th Edition) William D, Stevenson
Electrical Power J.B.Gupta
Generation, Distribution And Utilization Of Electrical Energy C.L.Wadawa
HDVC Power Transmission System Padiyar
Electromagnetic Force
Electromagnetics (2nd Edition) Administer
Analog
Electronic Devices And Circuit Theory Boylestad, Nashelsky
Micro Electronics (2nd Edition) Jacob Millman
Solid State Electronics (5th Edition) Streetman, Banerjee
Electronic Devices Salivahan, Suresh Kumar, Vallava Raj
Electronic Devices And Circuits Millman, Halkias
Pulse Digital And Switching Waveforms Millman, Taub
Integrated Electronics Millman, Halkias
Electrical Engineering And Basic Electronics G.B.Bharadwajan
Control Systems
Automatic Control Systems (7th Edition) KUO
Control Systems (1st Edition) Anagoor, Kani
Control Systems Engineering I.J.Nagrath, M.Gopal
Modern Control Engineering Ogata
Measurements
DC Machines Measurements & Measuring Insruments G.B.Bharadhwajan
Electrical And Electronic Measurement And Instrumentation A.K.Sawhney
Network Theory
Network Analysis Van, Valkenbarg
Network Theory "JNTU" Sudhakar, Shyam Mohan
Electronic Devices And Circuits (Problems And Solutions) Experienced Teachers
Electric Circuits (3rd Edition) Sudhakar, Shyam Mohan
Electronic Devices And Circuits (Problems And Solutions) Experienced Teachers
Electric Circuits (3rd Edition) Administer & Nahvi
Engineering Circuit Analysis (6th Edition) Hay T, Kemmerly, Durbin
Orkut????
A guy lost his girlfriend in a train accident.... but
the gal's name nowhere appeared in the dead list. This guy grew up n
became IT technical architect in his late 20's, achievement in itself!!
He hired developers from the whole globe and plan to make a software where he could search for his gf through the web..
Things went as planned...
n he found her, after losing millions of dollars and 3 long years!!
It was time to shut down the search operation, when the CEO of Google had a
word with this guy n took over this application,
This Software made a whopping 1 billion dollars profit in its first year,
which we today know as ORKUT.
The guy's name is Orkut Büyükkökten Yes
it's named after him only. Today he is paid a hefty sum by Google for
the things we do like scrapping. He is expected to b the richest person by 2009..
Orkut Büyükkökten today has 13 assistants to monitor his scrapbook & 8 to
monitor his friends-list. He gets around 20,000 friend-requests a day & about 85,000 scraps!!!
Some other Cool Facts about this guy:
* He gets $12 from Google when every person registers to this website.
* He also gets $10 when you add somebody as a friend.
* He gets $8 when your friend's friend adds you as a friend & gets $6 if
anybody adds you as friend in the resulting chain.
* He gets $5 when you scrap somebody & $4 when somebody scraps you.
* He also gets $200 for each photograph you upload on Orkut.
* He gets $2.5 when you add your friend in the crush-list or in the hot-list.
* He gets $2 when you become somebody's fan.
* He gets $1.5 when somebody else becomes your fan.
* He even gets $1 every time you logout of Orkut.
* He gets $0.5 every time you just change your profile-photograph.
* He also gets $0.5 every time you read your friend's scrap-book & $0.5 every time you view your friend's friend-list.
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