For those of you that are already experts in physics and engineering, you will most likely find this blog a bit elementary for you. Nonetheless, I’m writing it because I routinely get asked questions similar to this one on a daily basis. Many see a bit of contradiction. For example, the stars in the sky are clearly very far away and millions of light-years and the visible and non-visible radiation still seem to make it all the way to us on earth, yet it seems that some radios die out quickly even when there aren’t any obstacles in the path.So the short answer is that all of these waves, unless they run into something and get absorbed or scattered will theoretically go on forever at the speed of light. However, it is important to look at the relative energy of these waves. One of the key laws to the world of physics is the conservation of energy. There is a fixed amount of energy in the universe - you can’t make more, you can’t get rid of it, but you can change it from one form to another. Of course for most of you, this will cement the fact that these electromagnetic waves, unless they run into something will go on forever. And while we know that there is lots of stuff out there in the universe, it sure appears that there is a whole lot of empty space. Obviously that doesn’t tell the whole story.
Drop a pebble into a pool of water, the wave will extend away from the point of impact in a nice circle. As the wave gets farther from the center, the circle obviously gets bigger. In getting bigger, the energy in the wave is spread out over an ever expanding area. For the sake of the discussion, we will assume there is no impact to due to external forces so the energy of the whole wave remains the same. If we had an infinitely large pond of perfectly still water with a constant depth, the wave resulting from the pebble would technically go on forever in all directions. However, in doing so the magnitude (e.g. size) of the wave would get smaller. Unfortunately, the stone in water example is only two-dimensional. Electro-magnetic waves operate in three dimensions so we need to extend the metaphor a bit.
When we look at an ideal radiator of electromagnetic waves, we need to think isotropically. This means waves extending out equally in all directions from a point (a.k.a. a sphere). A good example might be a star like our very own sun. Just like the circle in the water, the electromagnetic energy spreads as the wave gets farther away, just like the surface area of a sphere. From our basic geometry we know that the surface area of a sphere of radius r is 4πr2 ; hence as we get farther from the transmitter, the power in the waves get “stretched” accordingly meaning that the resulting strength of the signal at any point is INVERSELY proportional to the square of the distance (r) from the transmitter (1 / 4πr2). It gets very small, very quickly, but never really gets to zero. This is often referred to as an inverse square law - as you know, gravity also works this way.
In this new Design News feature, "How it Works," we’re starting off by examining the inner workings of the electronic cigarette. While e-cigarettes seemed like a gimmick just two or three years ago, they’re catching fire -- so to speak. Sales topped $1 billion last year and are set to hit $10 billion by 2017. Cigarette companies are fighting back by buying up e-cigarette manufacturers.
Advertised as the "Most Powerful Tablet Under $100," the Kindle Fire HD 6 was too tempting for the team at iFixit to pass up. Join us to find out if inexpensive means cheap, irreparable, or just down right economical. It's teardown time!
The increased adoption of wireless technology for mission-critical applications has revved up the global market for dynamic electronic general purpose (GP) test equipment. As the link between cloud networks and devices -- smartphones, tablets, and notebooks -- results in more complex devices under test, the demand for radio frequency test equipment is starting to intensify.
Much of the research on lithium-ion batteries is focused on how to make the batteries charge more quickly and last longer than they currently do, work that would significantly improve the experience of mobile device users, as well EV and hybrid car drivers. Researchers in Singapore have come up with what seems like the best solution so far -- a battery that can recharge itself in mere minutes and has a potential lifespan of 20 years.
Some humanoid walking robots are also good at running, balancing, and coordinated movements in group settings. Several of our sports robots have won regional or worldwide acclaim in the RoboCup soccer World Cup, or FIRST Robotics competitions. Others include the world's first hockey-playing robot and a trash-talking Scrabble player.
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