THE DEFINITIVE BLOG FOR EVERYTHING YOU NEED TO KNOW ABOUT THE ENVIRONMENT YOU LIVE IN, WITH REFERENCE TO LIFE, EARTH AND COSMIC SPACE SCIENCES, PRESENTED BY ENVIRONMENTAL ENGINEER DORU INDREI, ENVIRONMENTAL QUALITY AND ENERGY SPACIALIST
"Life is not about what we know, but what we don't know, craving the unthinkable makes it so amazing, that is worth dying for."Doru Indrei
Nasa is to fire a space probe directly at the Sun to answer some of the most important questions about our solar system.
A small car-sized spacecraft will plunge into the sun's atmosphere approximately four million miles from its surface, exploring a region no other spacecraft has ever visited before.
The unprecedented project, named Solar Probe Plus, is scheduled to launch by 2018.
Nasa has selected five science investigations that will unlock the Sun's biggest mysteries as the probe repeatedly passes through its atmosphere.
‘This project allows humanity's ingenuity to go where no spacecraft has ever gone before,' said Lika Guhathakurta, Solar Probe Plus program scientist at NASA Headquarters, in Washington.
'For the very first time, we'll be able to touch, taste and smell our sun.'
As the spacecraft approaches the sun, its revolutionary carbon-composite heat shield must withstand temperatures exceeding about 1,400 degrees Celsius (2,550 degrees Fahrenheit) and blasts of intense radiation.
The spacecraft will have an up-close and personal view of the sun, enabling scientists to better understand and forecast the radiation environment for future space explorers.
‘The experiments selected for Solar Probe Plus are specifically designed to solve two key questions of solar physics - why is the sun's outer atmosphere so much hotter than the sun's visible surface and what propels the solar wind that affects Earth and our solar system? ' said Dick Fisher, director of NASA's Heliophysics Division in Washington.
'We've been struggling with these questions for decades and this mission should finally provide those answers'
NASA invited researchers in 2009 to submit science proposals. Thirteen were reviewed by a panel of NASA and outside scientists and the five selected investigations are receiving approximately $180 million for preliminary analysis, design, development and tests.
The Solar Wind Electrons Alphas and Protons Investigation will specifically count the most abundant particles in the solar wind - electrons, protons and helium ions - and measure their properties.
The investigation also is designed to catch some of the particles in a special cup for direct analysis.
A telescope on board will make 3-D images of the sun's corona, or atmosphere. The experiment actually will see the solar wind and provide 3-D images of clouds and shocks as they approach and pass the spacecraft.
Another will make direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the sun's atmospheric plasma.
The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft's antenna.
Another experiment from the Southwest Research Institute in San Antonio will look at elements in the sun's atmosphere using a mas spectrometer to weigh and sort ions in the vicinity of the spacecraft.
You've probably seen calculators with solar cells -- devices that never need batteries and in some cases, don't even have an off button. As long as there's enough light, they seem to work forever. You may also have seen larger solar panels, perhaps on emergency road signs, call boxes, buoys and even in parking lots to power the lights.
Although these larger panels aren't as common as solar-powered calculators, they're out there and not that hard to spot if you know where to look. In fact, photovoltaics -- which were once used almost exclusively in space, powering satellites' electrical systems as far back as 1958 -- are being used more and more in less exotic ways. The technology continues to pop up in new devices all the time, from sunglasses to electric vehicle charging stations.
The hope for a "solar revolution" has been floating around for decades -- the idea that one day we'll all use free electricity from the sun. This is a seductive promise, because on a bright, sunny day, the sun's rays give off approximately 1,000 watts of energy per square meter of the planet's surface. If we could collect all of that energy, we could easily power our homes and offices for free.
Photovoltaic Cells: Converting Photons to Electrons
The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity. A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays, like the one operating at Nellis Air Force Base in Nevada.
Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Ba¬sically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.
PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.
That's the basic process, but there's really much more to it. On the next page, let's take a deeper look into one example of a PV cell: the single-crystal silicon cell.
How Silicon Makes a Solar Cell
Silicon has some special chemical properties, especially in its crystalline form. An atom of silicon has 14 electrons, arranged in three different shells.
The first two shells -- which hold two and eight electrons respectively -- are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell.
The only problem is that pure crystalline silicon is a poor conductor of electricity because none of its electrons are free to move about, unlike the electrons in more optimum conductors like copper. To address this issue, the silicon in a solar cell has impurities -- other atoms purposefully mixed in with the silicon atoms -- which changes the way things work a bit. We usually think of impurities as something undesirable, but in this case, our cell wouldn't work without them.
Consider silicon with an atom of phosphorous here and there, maybe one for every million silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. It doesn't form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.
When energy is added to pure silicon, in the form of heat for example, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons, called free carriers, then wander randomly around the crystalline lattice looking for another hole to fall into and carrying an electrical current. However, there are so few of them in pure silicon, that they aren't very useful.
But our impure silicon with phosphorous atoms mixed in is a different story. It takes a lot less energy to knock loose one of our "extra" phosphorous electrons because they aren't tied up in a bond with any neighboring atoms. As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon. The process of adding impurities on purpose is called doping, and when doped with phosphorous, the resulting silicon is called N-type ("n" for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon.
The other part of a typical solar cell is doped with the element boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type ("p" for positive) has free openings and carries the opposite (positive) charge.
Anatomy of a Solar Cell
Before now, our two separate pieces of silicon were electrically neutral; the interesting part begins when you put them together. That's because without an electric field, the cell wouldn't work; the field forms when the N-type and P-type silicon come into contact. Suddenly, the free electrons on the N side see all the openings on the P side, and there's a mad rush to fill them. Do all the free electrons fill all the free holes? No. If they did, then the whole arrangement wouldn't be very useful. However, right at the junction, they do mix and form something of a barrier, making it harder and harder for electrons on the N side to cross over to the P side. Eventually, equilibrium is reached, and we have an electric field separating the two sides.
This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't climb it (to the P side).
When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side.
This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to the P side to unite with holes that the electric field sent there, doing work for us along the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.
There are a few more components left before we can really use our cell. Silicon happens to be a very shiny material, which can send photons bouncing away before they've done their job, so an antireflective coating is applied to reduce those losses. The final step is to install something that will protect the cell from the elements -- often a glass cover plate. PV modules are generally made by connecting several individual cells together to achieve useful levels of voltage and current, and putting them in a sturdy frame complete with positive and negative terminals.
How much sunlight energy does our PV cell absorb? Unfortunately, probably not an awful lot. In 2006, for example, most solar panels only reached efficiency levels of about 12 to 18 percent. The most cutting-edge solar panel system that year finally muscled its way over the industry's long-standing 40 percent barrier in solar efficiency -- achieving 40.7 percent [source: U.S. Department of Energy]. So why is it such a challenge to make the most of a sunny day?
Energy Loss in a Solar Cell.
Visible light is only part of the electromagnetic spectrum. Electromagnetic radiation is not monochromatic -- it's made up of a range of different wavelengths, and therefore energy levels.
Light can be separated into different wavelengths, which we can see in the form of a rainbow. Since the light that hits our cell has photons of a wide range of energies, it turns out that some of them won't have enough energy to alter an electron-hole pair. They'll simply pass through the cell as if it were transparent. Still other photons have too much energy.
Only a certain amount of energy, measured in electron volts (eV) and defined by our cell material (about 1.1 eV for crystalline silicon), is required to knock an electron loose. We call this the band gap energy of a material. If a photon has more energy than the required amount, then the extra energy is lost. (That is, unless a photon has twice the required energy, and can create more than one electron-hole pair, but this effect is not significant.) These two effects alone can account for the loss of about 70 percent of the radiation energy incident on our cell.
The familiar sight of a rainbow represents just a sliver of the greater electromagnetic spectrum.
Why can't we choose a material with a really low band gap, so we can use more of the photons? Unfortunately, our band gap also determines the strength (voltage) of our electric field, and if it's too low, then what we make up in extra current (by absorbing more photons), we lose by having a small voltage. Remember that power is voltage times current. The optimal band gap, balancing these two effects, is around 1.4 eV for a cell made from a single material.
We have other losses as well. Our electrons have to flow from one side of the cell to the other through an external circuit. We can cover the bottom with a metal, allowing for good conduction, but if we completely cover the top, then photons can't get through the opaque conductor and we lose all of our current (in some cells, transparent conductors are used on the top surface, but not in all). If we put our contacts only at the sides of our cell, then the electrons have to travel an extremely long distance to reach the contacts.
Remember, silicon is a semiconductor -- it's not nearly as good as a metal for transporting current. Its internal resistance (called series resistance) is fairly high, and high resistance means high losses. To minimize these losses, cells are typically covered by a metallic contact grid that shortens the distance that electrons have to travel while covering only a small part of the cell surface. Even so, some photons are blocked by the grid, which can't be too small or else its own resistance will be too high.
Solar-powering a House
What would you have to do to power your house with solar energy? Although it's not as simple as just slapping some modules on your roof, it's not extremely difficult to do, either.
First of all, not every roof has the correct orientation or angle of inclination to take full advantage of the sun's energy. Non-tracking PV systems in the Northern Hemisphere should ideally point toward true south, although orientations that face in more easterly and westerly directions can work too, albeit by sacrificing varying degrees of efficiency. Solar panels should also be inclined at an angle as close to the area's latitude as possible to absorb the maximum amount of energy year-round.
A different orientation and/or inclination could be used if you want to maximize energy production for the morning or afternoon, and/or the summer or winter. Of course, the modules should never be shaded by nearby trees or buildings, no matter the time of day or the time of year. In a PV module, if even just one of its cells is shaded, power production can be significantly reduced.
If you have a house with an unshaded, southward-facing roof, you need to decide what size system you need. This is complicated by the facts that your electricity production depends on the weather, which is never completely predictable, and that your electricity demand will also vary. Luckily, these hurdles are fairly easy to clear. Meteorological data gives average monthly sunlight levels for different geographical areas.
This takes into account rainfall and cloudy days, as well as altitude, humidity and other more subtle factors. You should design for the worst month, so that you'll have enough electricity year-round.
With that data and your average household demand (your utility bill conveniently lets you know how much energy you use every month), there are simple methods you can use to determine just how many PV modules you'll need. You'll also need to decide on a system voltage, which you can control by deciding how many modules to wire in series.
You may have already guessed a couple of problems that we'll have to solve. First, what do we do when the sun isn't shining?
Einstein called the cosmological constant his “greatest blunder.” Einstein was wrong. The cosmological constant was a neat idea for General Relativity that’s still important today, and General Relativity was, IMO, his greatest accomplishment. The idea that space and time are curved by matter and energy, and that curvature is what makes gravitational force is profound and beautiful, and profoundly affects the way I look at everything that involves Gravity.
But Einstein had his blunders, oh yes. The big thing Einstein was wrong about? Quantum mechanics. One of Einstein’s more memorable quotes was this: “God does not play dice with the Universe.”
What was this in reference to? In good ol’ regular, classical physics (including General Relativity), if you know all the initial conditions of your system and you know the laws of physics, you can figure out exactly what’s going to happen. In quantum mechanics, though, if you know the initial conditions and you know the laws of physics, you can figure out the probability of various outcomes happening, but you can never know which one will definitely occur until after it’s over. Einstein didn’t believe it, and held a series of great debates with Neils Bohr over the issue.
But this isn’t Lincoln-Douglas. This is physics. You want to settle something? You do it with an experiment. So Einstein (and his grad student, Nathan Rosen) tried to show that the Universe had to be deterministic. Their hope was that there are variables that we just haven’t seen yet that determine what’s going to happen. It doesn’t, and there’s now a theorem that tells us why. So Bohr was right, and Einstein was wrong. The Universe isn’t deterministic, not even according to the laws of physics.
But this is abstract. Let’s give you a concrete example of an experiment that you can do (well, in principle) to help you better understand this. Imagine I’ve got a big screen with two narrow slits that are very close together. And I’ve got a Cathode Ray Tube that shoots out electrons. If I leave both slits open and shoot a whole myriad of electrons, the electrons go through and act like waves.
They interfere with one another, and produce a nice pattern where they have constructive interference (where lots of electrons land) and destructive interference (where no electrons land). You can keep track of where the electrons land over time, and here’s what you see when you add it all up.
Cover either slit up, and the interference pattern goes away. So it needs two slits. What about electrons? What if you fire them one-at-a-time? Sure, electrons can interfere with other electrons. But, can one electron interfere with itself? What do we see if we shoot the electrons through the double slit experiment one at a time? Well, it takes a long time to get enough electrons to see, but here’s what the results are:
Amazing. The electron must be interfering with itself! How does it know where to go? And how do you determine which slit it went through?
Now, here’s where things get interesting. You can set up some light sensors on each of the slits to figure out which one the electrons go through. When the electron passes through the slit, if a photon (a particle of light) hits the electron, you know which slit it goes through. If a photon doesn’t hit it, you don’t know.
Here’s the crazy part: if you hit the electron with a photon, the interference pattern goes away. You force it to go through only one slit, and you just get two bumps on your screen, one for each of the two slits. If you don’t hit the electron, though, the electron does interfere with itself, and you get the interference pattern above.
If you look, and you try to know, you will destroy the quantum mechanical effects. If you don’t look, though, God plays dice while your back is turned.
It’s messed up. And it’s awesome. Was Einstein wrong? About quantum mechanics, yes. Yes he was. And that, my friends, is what Einstein’s greatest blunder really was. Einstein never accepted quantum mechanics, never accepted that this is the way the Universe works. If you can accept and understand this, then at least about this one thing, you’ll have taken a step that Einstein never did.
Bolts of lightning can travel as far as 25 miles or more. Lightning kills an average of 55 people in the United States each year. The only two safe places to be during a thunderstorm are in a car or in an enclosed house that has electricity and plumbing.
Britney Wehrle was walking with a friend on a sunny, warm day when she was suddenly struck by lightning, even though the sky above her was clear and blue.
And while that may sound like a rare or even freakish event, it's not that uncommon for lightning to travel far from its originating cloud, experts say. In some cases, bolts have struck as much as 25 miles from where they originated. Scientists refer to these wayward streaks of electricity as "bolts from the blue," since it often seems as though the lightning comes out of a clear blue sky.
As 11-year-old Wehrle recovers from a broken arm and a burn mark on her shoulder, it may be a good time to refresh your memory about how to protect yourself from lightning. At the top of the list: Avoid exposing yourself to it.
"When thunder roars, go indoors, and stay in there for 30 minutes after you hear the last thunder clap," said Susan Buchanan, spokeswoman for the National Weather Service in Silver Spring, Md., and a member of the agency's lightning safety team.
"Lightning is unpredictable," she added. "There's no safe place outdoors in a thunderstorm. If you remain outdoors during a thunderstorm, you are taking a gamble that you won't become one of the statistics."
And those statistics are staggering.
Every year, according to the National Weather Service, the Earth experiences 16 million thunderstorms. That amounts to an average of 1,800 storms happening at any given moment. Over the course of a year, 25 million bolts strike the ground, usually during thunderstorms but also during intense forest fires, heavy snowstorms, volcanic eruptions, nuclear detonations and large hurricanes.
Lightning kills an average of 55 people every year, Buchanan said, but it hits and severely injures hundreds more. According to calculations on NOAA's National Severe Storms Laboratory website, there is a one in 3,000 chance of getting killed or injured by lightning in your lifetime, assuming an average life span of 80 years. The chances of lightning hurting someone close to you is one in 300.
To form, lightning requires a specific combination of circumstances, said Vladimir Rakov, an electrical engineer and lightning expert at the University of Florida, Gainesville. The recipe includes hot temperatures on the ground and moist conditions, as well as strong updrafts that propel wet air into the cooler atmosphere, where it condenses and form clouds.
With its warmth, humidity and sea breezes that blow off two coasts, Florida experiences more lightning than any other state. But even there, clouds have to get high enough for ice to form, because electrification only happens within clouds that contain water in both its solid and liquid states.
As electric charges accumulate inside cloud, sparks start to fly, much like the sparks you sometimes see as you reach for a doorknob after shuffling your feet on a carpet. Some bolts travel within clouds. Others hit the ground. But exactly where a lightning bolt will end up is anyone’s guess. And often, it ends up in more than one place.
A flash of lightning can last for up to a second, Rakov explained, and each flash is usually made up of many strokes. Sometimes, those strokes all follow the same path. But studies show that between one-third and one half of flashes end up sending bolts to multiple end-points.
Why that happens isn't completely clear. One theory is that the first few strokes create a charge that repels subsequent strokes, diverting them elsewhere. Scientists also know that bolts can emerge from the side of a cloud and they may then travel for miles through long horizontal channels before eventually striking ground.
Whatever the cause, bolts from the blue can, on rare occasions, be deadly. The best thing people can do to avoid getting hit is to be vigilant of weather forecasts. If the radar shows storms approaching, Buchanan said, postpone outdoor activities. If you're outside and you hear thunder, go inside right away. And a pavilion doesn't count. Lightning can come in through the sides or travel through the ground.
There are only two absolutely safe places to be during a thunderstorm. One is in a metal car. The other is in a house with a roof, four walls, and plumbing and electric systems that can absorb the electricity of a lightning strike.
Once you’re inside, don't touch anything that's plugged into the wall. And stay away from sinks, bathtubs, showers, even toilets. Electricity travels efficiently through water and metal. In a car, don’t fiddle with the radio.
Buchanan couldn't emphasize enough her urgent advice to get inside as soon as you hear thunder. The majority of people who get struck, she said, had just waited too long before heading toward safety.
If you're camping in the wilderness and inside is not an option, stay away from tall isolated trees. Get off of hills and ridgelines in favor of low-lying areas -- though you should also watch out for flash flooding. Unfortunately, tents offer no protection from lightning.
"A lot of times people who are outside run for trees because they are more concerned about getting wet," Buchanan said. "But that makes them more vulnerable."
A bolt of lightning is a spark that connects the negatively charged bottom of a storm cloud with a positively charged surface (the Earth!). So let’s step back a few levels.
You’re probably familiar with the structure of the atom. An atom consists of a positively charged nucleus orbited by negatively charged electrons. Well, when two atoms or molecules collide, there’s a chance that some of these electrons will be ejected from the nuclei, resulting in a separation of positive and negative charge, where before you had a both in one neutral atom. The positive charge rests among the protons in the nucleus, and the negative charge with the now free electrons that have been bumped out.
In a cloud, molecules of water vapor are constantly rising and falling. As water on the ground gets heated up (whether by the sun or by you lighting a fire under a potful), molecules of water escape the liquid and fly through the air. This escape from liquid form is what we call evaporation.
Now, once the molecules have evaporated, they travel upwards. In fact, the whole mass of air and water vapor just above the ground moves upward in a convection current. A convection current is just the movement of fluid (that’s liquid or gas) that you get when you apply heat from one side. The heat causes the fluid to expand, decreasing its density.
The fluid in the surrounding area is not heated (or is heated much less), and so it stays the same density. So you have a parcel of air that is hotter and less dense than its surroundings. If you know how buoyancy works, you know that things which are less dense than their surroundings float, and this is just what happens with the heated air and water vapor. Now as the vapor rises with the air, the vapor molecules bump into other molecules. During these bumps, they may lose their electrons, becoming charged ions!
So does the water vapor just continue to rise into the air until it escapes from the Earth? No! And thank goodness, because otherwise there wouldn’t be much water around for us to survive off of! No, what happens is the water vapor continues to rise until its concentration in the air is greater than its solubility in the air solution. Let me explain what I mean by that.
Solubility is the measure of how much “stuff” you can dissolve into a uniform fluid like air or water. So for example the solubility of simple table salt, sodium chloride (NaCl) in water at 25°C is 35.9 grams per 100 milliliters. What that means is that a glass with 100ml of water could dissolve exactly 35.9g of salt. If you put 35.9g of salt into that glass, you would see it all disappear. You could also put 359g of salt into 1 liter, or 3590g of salt into 10 liters, and all the salt crystals would disappear. But if you added even one gram more in any of these examples, you would see salt crystals that would never dissolve.
This is because the concentration of salt has exceeded its solubility in the fluid. We say the fluid has reached its saturation point, and so any further addition of solute will not dissolve. Now here’s something really important: if you increase the temperature of the solution, the solubility of the thing being dissolved usually increases (there are some exceptions). Likewise, if you decrease the temperature of the solution, the solubility usually decreases.
For example, while salt’s solubility at 25°C is 35.9g/100ml, its solubility at 100°C is 39.1g/100ml and its solubility at 0°C is 35.6g/100mL. In practice this means that you can dissolve more salt in hotter water. So if you were to put 39.1g of salt in 100ml of water and raised the temperature of the water to 100°C, all of that salt would disappear – dissolved.
Now if you cooled that water to 25°C where the solubility of salt is 35.6g/100ml, some of that dissolved salt would come out of solution as salt crystals. In fact, 3.5g would come out of solution since that is the difference between the solubilities of salt at 100 and 25°C.
Well like I said before, air is a fluid, and it has a saturation point. And water vapor has a solubility in air just like salt has a solubility in water. And guess what? Temperature affects the solubility of water in air just like it affects the solubility of salt in water. Raise the temperature and you can get more water dissolved in the air. Lower the temperature and you can get some of the water to come out of the solution as water droplets. So let’s get back to water vapor. When we last left it, it had been heated by the sun and was rising along with a column of air due to convection.
As the water vapor gets higher and higher into the atmosphere, the temperature of the air decreases. As the water vapor gets into the colder air, some of the water molecules come out of solution, just like salt crystals coming out of solution when we chill the hot salt water. As they come out of solution, they form hydrogen bonds with their neighboring water molecules.
The formation of these bonds is exothermic, which means that when the bonds form, energy is released into the surrounding air and water vapor.* This energy heats up the air and vapor and sends it further up into the atmosphere, where the temperature is even colder! Now even more water vapor comes out of solution, forms hydrogen bonds, and boosts the parcel of air and vapor still further up into the atmosphere.
Eventually, at cold enough temperatures and high enough altitude, you run out of water vapor and this condensation-boost activity ceases. At this point gravity takes over and starts to pull the water droplets and ice particles that have formed back down to Earth. As they fall, they pass through warmer and warmer air, and are able to dissolve again as the temperature rises. This sends them back up through the cloud for another spin.
As they come back down, they will dissolve and head skywards once more. Because of this cycle, each water droplet makes many trips through the cloud. The result is many opportunities for collision, electron ejection, and the production of positively charged nuclei and free electrons.
Once this breaking apart of electrons from nuclei has occurred, the charges are separated in the storm cloud, with positive ions collecting at the top of the storm cloud and electrons gathering on the bottom. Why exactly this happens (and indeed even how the charges separate in the first place) is still up for debate. Isn’t that cool? Phenomena that occur all around the world and that have been observed by humans for a long time are still not understood! The world is still full of mysteries waiting to be solved, and you could be the one who solves them!
The charges separate. And they separate so that there’s a lot of positive charge at the top of the storm cloud and a lot of negative charge at the bottom of it. So you can imagine the bottom of a thunder cloud brimming with electrons, while the top part of it has lots of atoms without their electrons (positive ions).
Now, you probably know that like charges repel, and this physical law is very important to how lightning works. The big bank of negative electrons at the bottom of the cloud pushes the electrons in the surface of the Earth downward, deeper into the crust of the Earth. The result of this is that you now have a huge bank of negative charge at the bottom of the cloud and a huge bank of positive charge at the surface of the Earth.
Now, whenever you have a huge difference in charge like this (or if you like, a high voltage), it will be resolved if the charges have a path that they can meet through. For instance, if I ran a copper wire from the base of the cloud to the Earth, the electrons in the cloud could flow down into the Earth and neutralize the difference in charge, and in fact this is one tested way of triggering lightning.
Metal is a good conductor, meaning electrons can flow through it very easily. It’s a good conductor because the electrons in a metal are not tightly bound to their nuclei – they can move about a bit, and if there’s a reason that they should be moving (say a big positive charge attracting them), those electrons can flow right through the metal. But air, like the air separating the cloud from the Earth, is a very bad conductor (we call it an insulator for this reason). The electrons in the molecules making up the air are bound very tight, and they resist being moved around even when there is a positive charge attracting them. Add to that the fact that gasses at room temperature are about 1000x less dense than liquids and you should be able to understand why air is a poor conductor.
However, even air has its breaking point. If you get enough of a charge difference (high enough voltage), the air can become ionized as the massive banks of charge rip electrons away from nuclei and send them careening into other nuclei, often freeing more electrons. Once the air is ionized, it becomes a much better conductor, and electrons can flow through it just like electricity through a wire. This is what happens when lightning strikes.
First, the huge difference in charge causes the air to ionize in the immediate area of the cloud base. Then, the air continues to ionize in a branching path down to the Earth, searching out the positive ground. You might expect the lightning bolt to travel straight down to Earth (as we know a straight line is the fastest path between two points), but instead it forks and branches and gives us the lightning pattern we all recognize.
This tortuous, branching path is the path of least resistance, the path with the most ionized and best conducting air. So when you look at a forked lightning bolt, you can tell that wherever the bolt goes is the path that best conducted electricity at that moment in time. Now this ionized air with electrons flowing through it (called a stepped leader because it proceeds in discrete little “steps” of movement) continues to branch and fork and wind its way toward the Earth and those positive charges it so longs for.
At the same time, that positive charge in the Earth begins reaching up towards the clouds, and for the same reasons. The air becomes ionized and the positive charge can climb upwards. These upward reaching paths of ionized air are called positive streamers, and they look like small, purplish lightning bolts. You can actually see them! They usually form at the top of tall, conductive objects like trees, lightning rods, or even humans.
Now check out this high speed photography video of a lightning strike. You’ll see the stepped leaders coming down, branching a lot. Eventually one reaches the bottom and KABLAMMO! The charges drain and you get the massive flash.
Finally, after much searching, one of the branches of the ionized air touches a positive streamer! The circuit is completed, and electrons in the cloud and in the rest of the branches flow rapidly down the path of ionized air in a blinding flash of light and heat.
This electrical discharge, this super fast transit of electrons from negative cloud bank to positive ground, is what we call a lightning bolt. It is a force to be reckoned with! In a single strike of lightning, about 30,000,000,000,000,000,000 electrons rush from cloud to Earth, superheating the ionized path of air that it travels through and dealing tremendous damage to anything it touches.*** Sand, for instance, is fused into glass. When trees are struck by lightning, the flow of electricity superheats the sap of the tree, which expands rapidly, causing the tree to explode spectacularly!
Haven’t you heard of people who have survived being struck by lightning? How could they possibly survive if lightning is powerful enough to fuse sand into glass or explode a tree? The key is in the constitution of a person.
See, in a tree, the bark of the tree is a poor conductor but the inner sap is a good conductor, so the bolt travels through the inside of the tree, superheating the sap and exploding the tree. But the outside of a human, especially a human that has been coated in water by a thunderstorm, is a very good conductor.
As a result, the bolt can travel around the human and into the ground. Still, the effects are very damaging, and the moisture on the person’s skin quickly superheats and boils, giving the person severe steam burns. If the person has a lot of moisture trapped anywhere on their body, for instance in a waterlogged hat or shoes, these items can explode due to the superheating from the lightning bolt, causing terrible damage.
But just because a person can survive lightning, doesn’t mean it isn’t very, very dangerous. Indeed, though you have a chance of having a painful but not lethal experience with lightning, you also have a good chance of sudden, painful death! If you’re lucky enough for the bolt to travel along the outside of your body, you still might die from the burns. Or, if it passes straight through you, it will simply incinerate your internal tissues. Another fun option is that sufficient current could pass through your brain or heart, disrupting their electrical flow and stopping your vital functions!
Luckily, there are plenty of ways to stay safe from lightning! Watch weather forecasts and avoid being outside during storms. Don’t wave golf clubs or umbrellas around in the air. If you get caught in a storm, take shelter inside a house with a lightning rod or in a car. If lightning strikes either of these, it will travel down the path of least resistance (the lightning rod or the metal shell of the car) and pass harmlessly into the ground.
Never take shelter under a tree, as lightning could hit the tree and cause it to explode right in your face! Yikes. And if you ever find your hair standing up while outside in a lightning storm, you need to take immediate action. If this happens, it means you are giving off positive streamers and are about to be the last segment of the path of least resistance! Immediately crouch to the ground (don’t lie down) and make yourself small. If you’re lucky, the bolt will find another way to the ground and you will live to see another day.
So you see, lightning is really awesome and amazing, and it happens all the time on our little Earth. So next time you’re in a thunderstorm, think about what is really happening each time you hear that rumble, and appreciate the simple and elegant physics of the lightning bolt!
Now, I leave you with fun facts about lightning.
-Lightning travels at 130,000 mph.
-Lightning heats the air it travels through to 54,000°F (30,000°C). That’s hotter than the surface of the Sun!
-Over eight million lightning strikes occur each day on Earth. That means one hundred strikes every second!
-The dust and gas given off by erupting volcanoes rubs together in a similar way to water molecules and can produce lightning as well!
-Lightning bolts have been observed giving off small amounts of gamma radiation!
-There are all kinds of cool and exotic lightning bolts, such as 50km tall “sprites” that reach high into the atmosphere from the top of clouds!
In 1925, Albert Einstein predicted the existence of the atom laser, a completely different type of laser, but until now, no one could actually build one, so it was considered almost a practical impossibility. For the first time, a team of Italian scientists managed to create such a device. The word Laser is an acronym for "light amplification by stimulated emission of radiation". Lasers are possible because of the way light interacts with electrons and the beam consists entirely of photons, released by electrons as excess energy, when they drop from an outer to an inner level.
Much like an optical laser, an atom laser is a coherent beam that behaves like a wave, but no one had managed to create a coherent beam of atoms instead of photons. Massimo Inguscio and colleagues at the Florence University, Italy, created the first functioning laser, more than eight decades after it had been theorized by Einstein.
So far, every attempt to build such a laser failed because of the same problem, the impossibility of stopping atoms from bouncing into one another, which prevented the formation of a coherent beam.
As Inguscio said, "an atomic laser is eagerly awaited in the field of micro-electronics" with many potential applications in various devices and sensors, like atom holography images, having a much higher resolution than conventional holographic images.
They achieved the much wanted coherence of the beam by using potassium isotopes to build an "atomic condensate" squeezed into a harmonious whole by a magnetic field, much like Einstein and Satyendra Nath Bose envisioned long ago, in what is now known as a Bose-Einstein condensate of atoms, a state of matter formed by a system of bosons confined in an external potential and cooled to temperatures very near to absolute zero (0 kelvin or −273.15 °C).
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