|MLA Citation:||Bloomfield, Louis A. "Electric Power Generation" How Everything Works 19 Mar 2018. Page 3 of 4. 19 Mar 2018 <http://www.howeverythingworks.org/prints.php?topic=electric_power_generation&page=3>.|
The blades don't keep this newly acquired energy. Instead, they do work on a generator. The generator, which consists of a rotating magnet that spins within stationary coils of wire, uses this energy to generate electricity. The amount of power that a windmill generates depends on the wind speed and the windmill's size, but large windmills can generate in excess of a million watts of electric power.
Of course, a real metal detector is much more sensitive than your hands are, but it's using similar principles to detect nearby metal. Most often, a metal detector uses a coil of wire with an alternating current in it to create a rapidly changing magnetic field around the coil. If that changing magnetic field enters a piece of nearby metal, the metal responds. If the metal is ferromagnetic—meaning that it has intrinsic magnetic order like iron or steel—it will respond strongly with its own magnetic field. If the metal is non-ferromagnetic—meaning that it doesn't have the appropriate intrinsic magnetic order—it will respond more weakly with magnetic fields that are caused by electric currents that begin to flow through it.
In a short range metal detector, the detector looks for the direct interaction of its magnetic field and a nearby piece of metal. That nearby metal changes the characteristics of the detector's wire coil in a way that's relatively easy to detect. But in a longer-range metal detector, the electromagnetic coil must actually radiate an electromagnetic wave and then look for the reflection of this electromagnetic wave from a more distant piece of metal. That's because the magnetic field of the coil doesn't extend outward forever—it dies away a few diameters of the coil away from the coil itself. For the metal detector to look for metal farther away, it needs help carrying the magnetic field through space. By combining an electric field with the magnetic field, the long-range metal detector creates an electromagnetic wave—a radio wave—that travels independently through space. Electromagnetic waves reflect from many things, particularly objects that conduct electricity. So the long-range metal detector launches an electromagnetic wave and then looks for the reflection of that wave. This wave reflection technique is the basis for sonar (sound waves) and radar (radio waves), and it can be used to find metals deep in the ground. Unfortunately, the ground itself conducts electricity to some extent, so it becomes harder and harder to distinguish the reflections from metal from the reflections from other things in the ground.
By itself, an overheated photocell won't fail dramatically; it will just stop working. If you've overheated it severely, it will remain broken from then on. But if the photocell is part of a larger collection of power generating elements that continues to produce power, that photocell may suddenly consume all of the power from the other elements. In that case, the photocell may explode as its temperature skyrockets.
When an electron, which is negatively charged, approaches the depletion region from the anode side, it first encounters the depletion region's negatively charged surface and is repelled. But when the electron approaches from the cathode side, it first encounters the depletion region's positively charged surface and is attracted. If it has enough energy when it approaches the depletion region from the cathode side, the electron can cross the depletion region to reach the anode layer. Thus electrons can move relatively easily from the photocell's cathode layer to its anode layer but they can't go back.
When a photocell is exposed to light, some of the light particles (photons) are absorbed in the diode's cathode layer. When such an absorption occurs, the photon's energy may be transferred to an electron in the cathode, giving that electron the energy it needs to cross the depletion region and reach the anode. But once the electron has arrived at the anode it can't return to the cathode directly across the depletion region. Instead, it must flow through an external circuit in order to return to the cathode. As that electron flows through the external circuit, it can give up some of its energy, obtained from the light photon, to devices in that circuit. In that manner, light energy has provided energy to an electrically powered device.
Second, to make efficient use of the wind created by traffic, hundreds of wind generators would have to be installed on each mile of expressway. Since wind generators are expensive, it's much more cost effective to put them on windy ridges out in the country or by the seashore.
Third, the wind generators you propose would actually extract energy from the cars and trucks and reduce their gas mileages! That fact might surprise you, since it would seem that extracting energy from the wind wouldn't have any effect on the cars and trucks that created that wind. But the wind and the vehicles continue to interact as they move along the expressway—each vehicle drags a pocket of air with it and interfering with this air pocket has the effect of interfering with the vehicle! The vehicle uses energy to maintain this moving air pocket and it burns additional fuel. An aerodynamically well-designed vehicle has a relatively small air pocket, but there is a limit to what can be done. To reduce the energy cost of maintaining the air pocket, the vehicle's driver can steer it into the air pocket behind another vehicle so that the two vehicles share a single air pocket. The lead vehicle then provides most of the energy needed to keep the air pocket moving. This technique of sharing an air pocket is called "drafting" and is frequently used by bicycle racers. But while drafting makes it easier for many vehicles to keep their air pockets moving, the wind generators that you propose would make it harder—they would steal energy from the air pockets of every passing vehicle and make those vehicles fight harder to keep their air pockets moving.
A better way to save energy would be to encourage large-scale drafting in some safe way. Having chains of independent cars tailgate one another would be energy efficient, but would cause horrific accidents. However, assembling those cars into a tightly coupled "train" may someday become possible with advances in technology and computer controls.
There is, however, an alternative explanation: you may have seen the "green flash" that occasionally appears just as the sun reaches the horizon at sunrise or sunset. This flash is a refraction effect in the atmosphere in which only blue-green light from the sun reaches the viewer's eyes for a second or two while the sun is just below the horizon. However, this green flash should appear in the eastern sky just before dawn, not the southern sky.
Increasing the current in the generator also affects its magnetic fields because currents are magnetic. At a low current, the current's magnetism can be ignored. But when a generator is handling a very large current, the magnetic fields associated with that current are no longer small perturbations on the generator's normal magnetic fields and the generator may not perform properly any more.
Finally, a generator's job is to transfer energy from a mechanical system to the electric current passing through it. As the amount of current in the generator increases, the amount of work that the mechanical system provides must also increase—the generator becomes harder to turn. There will always be a limit to how much torque an engine or crank can exert on the generator to keep it spinning and thus there will be a limit to how much current the generator can handle.
As for how the current varies with load: the more current the load permits to pass through it, the more current will pass through the generator. Assuming that the generator is well built and has very little electric resistance, the load will serve to limit the current. The generator will then deliver just as much current as the load will permit. If the load permits more current, the generator will deliver more. As a result, the wires in the generator will waste more power as heat, the magnetic fields in the generator will become more complicated, and the device powering the generator will have to work harder to keep the generator turning.
Nonetheless, a large permanent magnet isn't really permanent. The random fluctuations of thermal energy and the influences of passing magnetic fields gradually demagnetize large permanent magnets. However, good permanent magnets demagnetize so slowly that the changes are completely undetectable. You might have to wait a billion years to detect any significant weakening in the magnetic field around such a magnet.
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