No. Birds do this all the time. What protects the bird is the fact that it doesn’t complete a circuit. It touches only one wire and nothing else. Although there is a substantial charge on the power line and some of that charge flows onto the bird when it lands, the charge movement is self-limiting. Once the bird has enough charge on it to have the same voltage as the power line, charge stops flowing. And even though the power line’s voltage rises and falls 60 times a second (or 50 times a second in some parts of the world), the overall charge movement at 10,000 volts just isn’t enough to bother the bird much. At 100,000 volts or more, the charge movement is uncomfortable enough to keep birds away, so you don’t see them landing on the extremely high-voltage transmission lines that travel across vast stretches of countryside.

The story wouldn’t be the same if the bird made the mistake of spanning the gap from one wire to another. In that case, current could flow through the bird from one wire to the other and the bird would run the serious risk of becoming a flashbulb. Squirrels occasionally do this trick when they accidentally bridge a pair of wires. Some of the unexpected power flickers that occur in places where the power lines run overhead are caused by squirrels and occasionally birds vaporizing when they let current flow between power lines.

Power outages come in a variety of types, one of which involves a substantial decrease in the voltage supplied to your home. The most obvious effect of this voltage decrease is the dimming of the incandescent lights, which is why it's called a "brownout." The filament of a lightbulb is poor conductor of electricity, so keeping an electric charge moving through it steadily requires a forward force. That forward force is provided by the voltage difference between the two wires: the one that delivers charges to the filament and the one that collects them back from the filament. As the household voltage decreases, so does the force on each charge in the filament. The current passing through the filament decreases and the filament receives less electric power. It glows dimly.

At the risk of telling you more than you ever want to know, I'll point out that the filament behaves approximately according to Ohm's law: the current that flows through it is proportional to the voltage difference between its two ends. The larger that voltage difference, the bigger the forces and the more current that flows. This ohmic behavior allows incandescent lightbulbs to survive decreases in voltage unscathed. They don't, however, do well with increases in voltage, since they'll then carry too much current and receive so much power that they'll overheat and break. Voltage surges, not voltage decreases, are what kill lightbulbs.

The other appliances you mention are not ohmic devices and the currents that flow through them are not simply proportional to the voltage supplied to your home. Motors are a particularly interesting case; the average current a motor carries is related in a complicated way to how fast and how easily it's spinning. A motor that's turning effortlessly carries little average current and receives little electric power. But a motor that is struggling to turn, either because it has a heavy burden or because it can't obtain enough electric power to overcome starting effects, will carry a great deal of average current. An overburdened or non-starting motor can become very hot because it's wiring deals inefficiently with the large average current, and it can burn out. While I've never heard of a refrigerator motor dying during a brownout, it wouldn't surprise me. I suspect that most appliance motors are protected by thermal sensors that turn them off temporarily whenever they overheat.

Modern electronic devices are also interesting with respect to voltage supply issues. Electronic devices operate on specific internal voltage differences, all of which are DC — direct current. Your home is supplied with AC — alternating current. The power adapters that transfer electric power from the home's AC power to the device's DC circuitry have evolved over the years. During a brownout, the older types of power adapters simply provide less voltage to the electronic devices, which misbehave in various ways, most of which are benign. You just want to turn them off because they're not working properly. It's just as if their batteries are worn out.

But the most modern and sophisticated adapters are nearly oblivious to the supply voltage. Many of them can tolerate brownouts without a hitch and they'll keep the electronics working anyway. The power units for laptops are a case in point: they can take a whole range of input AC voltages because they prepare their DC output voltages using switching circuitry that adjusts for input voltage. They make few assumptions about what they'll be plugged into and do their best to produce the DC power required by the laptop.

In short, the motors in your home won't like the brownout, but they're probably protected against the potential overheating problem. The electronic appliances will either misbehave benignly or ride out the brownout unperturbed. Once in a while, something will fail during a brownout. But I think that most of the damage is down during the return to normal after the brownout. The voltages bounce around wildly for a second or so as power is restored and those fluctuations can be pretty hard some devices. It's probably worth turning off sensitive electronics once the brownout is underway because you don't know what will happen on the way back to normal.

A transformer's current regulation involves a beautiful natural feedback process. To begin with, a transformer consists of two coils of wire that share a common magnetic core. When an alternating current flows through the primary coil (the one bringing power to the transformer), that current produces an alternating magnetic field around both coils and this alternating magnetic field is accompanied by an alternating electric field (recall that changing magnetic fields produce electric fields). This electric field pushes forward on any current passing through the secondary coil (the one taking power out of the transformer) and pushes backward on the current passing through the primary coil. The net result is that power is drawn out of the primary coil current and put into the secondary coil current.

But you are wondering what controls the currents flowing in the two coils. The circuit it is connected to determines the current in the secondary coil. If that circuit is open, then no current will flow. If it is connected to a light bulb, then the light bulb will determine the current. What is remarkable about a transformer is that once the load on the secondary coil establishes the secondary current, the primary current is also determined.

Remember that the current flowing in the secondary coil is itself magnetic and because it is an alternating current, it is accompanied by its own electric field. The more current that is allowed to flow through the secondary coil, the stronger its electric field becomes. The secondary coil's electric field opposes the primary coil's electric field, in accordance with a famous rule of electromagnetism known as Lenz's law. The primary coil's electric field was pushing backward on current passing through the primary coil, so the secondary coil's electric field must be pushing forward on that current. Since the backward push is being partially negated, more current flows through the primary coil.

The current in the primary coil increases until the two electric fields, one from the primary current and one from the secondary current, work together so that they extract all of the primary current's electrostatic energy during its trip through the coil. This natural feedback process ensures that when more current is allowed to flow through the transformer's secondary coil, more current will flow through the primary coil to match.

The bulb will operate perfectly well, regardless of which way you connected the lamp's two wires. Current will still flow in through one wire, pass through the bulb's filament, and return to the power company through the other wire. The only shortcoming of reversing the connections is that you will end up with the "hot" wire connected to the outside of the socket and bulb, rather than to the central pin of the socket and bulb. That's a slight safety issue: if you touch the hot wire with one hand and a copper pipe with the other, you'll get a shock. That's because a large voltage difference generally exists between the hot wire and the earth itself.

In contrast, there should be very little voltage difference between the other wire (known as "neutral") and the earth. In a properly wired lamp, the large spade on the electric plug (the neutral wire) should connect to the outside of the bulb socket. That way, when you accidentally touch the bulb's base as you screw it in or out, you'll only be connecting your hand to the neutral wire and won't receive a shock. If you miswire the lamp and have the hot wire connected to the outside of the socket, you can get a shock if you accidentally touch the bulb base at any time.

Popular in movies as a source of long glowing sparks, a Tesla coil is basically a high-frequency, very high-voltage transformer. Like most transformers, the Tesla coil has two circuits: a primary circuit and a secondary circuit. The primary circuit consists of a capacitor and an inductor, fashioned together to form a system known as a "tank circuit". A capacitor stores energy in its electric field while an inductor stores energy in its magnetic field. When the two are wired together in parallel, their combined energy sloshes back and forth from capacitor to inductor to capacitor at a rate that's determined by various characteristics of the two devices. Powering the primary of the Tesla coil is a charge delivery system that keeps energy sloshing back and forth in the tank circuit. This delivery system has both a source of moderately high voltage electric current and a pulsed transfer system to periodically move charge and energy to the tank. The delivery system may consist of a high voltage transformer and a spark gap, or it may use vacuum tubes or transistors.

The secondary circuit consists of little more than a huge coil of wire and some electrodes. This coil of wire is located around the same region of space occupied by the inductor of the primary circuit. As the magnetic field inside that inductor fluctuates up and down in strength, it induces current in the secondary coil. That's because a changing magnetic field produces an electric field and the electric field surrounding the inductor pushes charges around and around the secondary coil. By the time the charges in the secondary coil emerge from the coil, they have enormous amounts of energy; making them very high voltage charges. They accumulate in vast numbers on the electrodes of the secondary circuit and push one another off into the air as sparks.

While most circuits must form complete loops, the Tesla coil's secondary circuit doesn't. Its end electrodes just spit charges off into space and let those charges fend for themselves. Many of them eventually work their ways from one electrode to the other by flowing through the air or through objects. But even when they don't, there is little net build up of charge anywhere. That's because the direction of current flow through the secondary coil reverses frequently and the sign of the charge on each electrode reverses, too. The Tesla coil is a high-frequency device and its top electrode goes from positively charged to negatively charge to positively charged millions of times a second. This rapid reversal of charge, together with reversing electric and magnetic fields means that a Tesla coil radiates strong electromagnetic waves. It therefore interferes with nearby radio reception.

Finally, it has been pointed out to me by readers that a properly built Tesla coil is resonant--that the high-voltage coil has a natural resonance at the same frequency that it is being excited by the lower voltage circuit. The high-voltage coil's resonance is determined by its wire length, shape, and natural capacitance.

A transformer transfers power between two or more electrical circuits when each of those circuits is carrying an alternating electric current. Transfers of this sort are important because many electric power systems have incompatible circuits--one circuit may use large currents of low voltage electricity while another circuit may use small currents of high voltage electricity. A transformer can move power from one circuit of the electric power system to another without any direct connections between those circuits.

Now for the technical details: a transformer is able to make such transfers of power because (1) electric currents are magnetic, (2) the magnetic fields from an alternating electric current changes with time, (3) a time-varying magnetic field creates an electric field, and (4) an electric fields pushes on electric charges and electric currents. Overall, one of the alternating currents flowing through a transformer creates a time-varying magnetic field and thus an electric field in the transformer. This electric field does work on (transfers power to) another alternating current flowing through the transformer. At the same time, this electric field does negative work on (saps power from) the original alternating current. When all is said and done, the first current has lost some of its power and the second current has gained that missing power.

Your lights are dimming because something is reducing the voltage of the electricity in your house. The lights expect the electric current passing through them to experience a specific voltage drop--that is, they expect each electric charge to leave behind a certain amount of energy as the result of its passage through the lights. If the voltage of electricity in your house is less than the expected amount, the lights won't receive enough energy and will glow dimly.

The most probable cause for this problem is some power-hungry device in or near your house that cycles on every 5 or 10 minutes. In all likelihood, this device contains a large motor--motors have a tendency to draw enormous currents while they are first starting to turn, particularly if they are old and in need of maintenance. The wiring and power transformer systems that deliver electricity to your neighborhood and house have limited capacities and cannot transfer infinite amounts of power without wasting some of it. In general, wires waste power in proportion to the square of the current they are carrying. While the amount of power wasted in your home's wiring is insignificant in normal situations, it can become sizeable when the circuits are overloaded. This wasted power in the wiring appears as a loss of voltage--a loss of energy per charge--at your lights and appliances. When the heavy equipment turns on and begins to consume huge amounts of power, the wiring and other electric supply systems begin to waste much more power than normal and the voltage reaching your lights is significantly reduced. Your lights dim until the machinery stops using so much power.

To find what device that's making your lights dim, listen carefully the next time your lights fade. You'll probably hear an air conditioner, a fan, or even an elevator starting up somewhere, either in your house or in your neighborhood. There may be nothing you can do to fix the problem, but it's possible that replacing a motor or its bearings will reduce the problem. Another possible culprit is an electric heating system--a hot water heater, a radiant heater, an oven, a toaster, or even a hair-dryer. These devices also consume large amounts of power and, in an older house with limited electric services, may dim the lights.

Europe uses alternating current, just as we do, however some of the characteristics of that current are slightly different. First, Europe uses 50 cycle-per-second current, meaning that current there reverses directions 100 times per second. That's somewhat slower than in the U.S., where current reverses 120 times per second (60 full cycles of reversal each second or 60 Hz). Second, their standard voltage is 230 volts, rather than the 120 volts used in the U.S.

While some of our appliances won't work in Europe because of the change in cycles-per-second, the biggest problem is with the increase in voltage. The charges entering a U.S. appliance in Europe carry about twice the energy per change (i.e. twice the voltage) and this increased "pressure" causes about twice the number of charges per second (i.e. twice the current) to flow through the appliance. With twice the current flowing through the appliance and twice as much voltage being lost by this current as it flows through the appliance, the appliance is receiving about four times its intended power. It will probably burn up.

They contain highly purified and refined chemicals and are actually marvels of engineering. It's more surprising to me that they are so cheap, given how complicated they are to make.

It's useful to describe moving electric charges as a current and for that current to flow in the direction that the charges are moving. Suppose that we define current as flowing in the direction that electrons take and look at the result of letting this current of electrons flow into a charge storage device. We would find that as this current flowed into the storage device, the amount of charge (i.e. positive) charge in that device would decrease! How awkward! You're "pouring" something into a container and the contents of that container are decreasing! So we define current as pointing in the direction of positive charge movement or in the direction opposite negative charge movement. That way, as current flows into a storage device, the charge in that device increases!

The bulb in a battery doesn't care which way current flows through it. The metal has no asymmetry that would treat left-moving charges differently from right-moving charges. That's not true of the transistors in a walkman or gameboy. They contain specialized pieces of semiconductor that will only allow positive charges to move in one direction, not the other. When you put the batteries in backward and try to propel current backward through its parts, the current won't flow and nothing happens.

Your body is similar to salt water and is thus a reasonably good conductor of electricity. Once current penetrates your skin (which is insulating), it flows easily through you. At high currents, this electricity can deposit enough energy in you to cause heating and thermal damage. But at lower currents, it can interfere with normal electrochemical and neural process so that your muscles and nerves don't work right. It takes about 0.030 amperes of current to cause serious problems for your heart, so that currents of that size can be fatal.

When you complete a circuit by plugging an appliance into an electrical outlet, current flows out one wire to the appliance and returns to the electric company through the other wire. With alternating current, the roles of the two wires reverse rapidly, so that at one moment current flows out the black wire to the appliance and moments later current flows out the white wire to the appliance. But the power company drives this current through the wires by treating the black wire specially--it alternately raises and lowers the electrostatic potential or voltage of the black wire while leaving the voltage of the white wire unchanged with respect to ground. When the voltage of the black wire is high, current is pushed through the black wire toward the appliance and returns through the white wire. When the voltage of the black wire is low, current is pulled through the black wire from the appliance and is replaced by current flowing out through the white wire.

The white wire is rather passive in this process because its voltage is always essentially zero. It never has a net charge on it. But the black wire is alternately positively charged and then negatively charged. That's what makes its voltage rise and fall. Since the black wire is capable of pushing or pulling charge from the ground instead of from the white wire, you don't want to touch the black wire while you're grounded. You'll get a shock.

Your hot water heater is powered by 240 volt electric power through the two black wires. Each black wire is hot, meaning that its voltage fluctuates up and down significantly with respect to ground. In fact, each black wire is effectively 120 volts away from ground on average, so that if you connected a normal light bulb between either black wire and ground, it would light up normally. However, the two wires fluctuate in opposite directions around ground potential and are said to be "180° out of phase" with one another. Thus when one wire is at +100 volts, the other wire is at -100 volts. As a result of their out of phase relationship, they are always twice as far apart from one another as they are from ground. That's why the two wires are effectively 240 volts apart on average.

Most homes in the United States receive 240 volt power in the form of two hot wires that are 180° out of phase, in addition to a neutral wire. 120-volt lights and appliances are powered by one of the hot wires and the neutral wire, with half the home depending on each of the two hot wires. 240-volt appliances use both hot wires.

A transformer only works with ac current because it relies on changes in a magnetic field. It is the changing magnetic field around the transformer's primary coil of wire that produces the electric field that actually propels current through the transformer's secondary coil of wire.

When dc current passes through the primary coil of wire, the coil does have a magnetic field around it, but it doesn't have an electric field around it. The electric field is what pushes electric charges through the secondary coil to transfer power from the primary coil to the secondary coil. In contrast, when ac current passes through that primary coil of wire, the magnetic field around the coil flips back and forth in direction and this changing magnetic field gives rise to an electric field around the coil. It is this electric field that pushes on electrically charged particles--typically electrons--in the secondary coil of wire. These electrons pick up speed and energy as they move around the secondary coil's turns. The more turns these charged particles go through, the more energy they pick up. That's why doubling the turns in a transformer's secondary coil doubles the voltage of the current leaving the secondary coil.

Generating heat from a battery is relatively easy. All you need is a material that conducts electricity only moderately well and you're in business. If you allow current to flow through that material from the battery's positive terminal to its negative terminal, the current will lose energy as it struggles to get through the material and the current's lost energy will become thermal energy in the material. The only difficult part of this task is in choosing the right material so that it doesn't produce too much or too little heat. In short, the electric resistance of the finished material has to be in the right range. For a solid system that you can cut and tailor, that's not much of a problem. But for a paint, it could be tricky. To make an inexpensive paint, it would probably need to use carbon powder as the electric conductor. A thin layer of carbon granules held in place by a plastic of some sort would probably provide a suitable conducting surface that would become warm when you allowed current to flow through it from a battery. There are copper and silver conducting paints that might also work, but these are rather expensive and I'm not sure how they behave at elevated temperatures.

The frequency characteristics of a transformer are determined principally by the materials in the transformer's core. Power flows from the primary circuit to the secondary circuit by way of the magnetization of the transformer's core. With each half-cycle of the alternating current in the primary circuit, the transformer's core must magnetize and demagnetize. A transformer core's ability to magnetize and demagnetize properly depends on the frequency of the alternating current in the transformer's coils. If that frequency is too low, the core may saturate--reach its maximum possible magnetization--during the half-cycle. In that case, the core will not be able to transfer the requisite amount of energy to the secondary coil and the power transferred between the two coils will be inadequate. That's why low frequency transformers often contain huge iron cores--cores that avoid saturation by spreading out the magnetization and stored energy over large volumes of iron.

On the other hand, if the frequency of current in the primary is too high, the core may be unable to magnetize and demagnetize fast enough to keep up with it and the power transfer will again be inadequate. The core may also become hot due to friction-like losses in the core material. That's why high frequency transformers use special core materials such as ferrite powders or even air. Although air (or really empty space) can't store large amounts of energy in small volumes when it magnetizes, it can respond extremely quickly. Air-core transformers operate well at extremely high frequencies.

If an appliance receiving power from an AC power source behaves as an electric resistor--meaning that the current passing through it is proportional to the voltage drop across it--then it's easy to calculate the power being consumed by this appliance. You simply multiply the voltage drop across the appliance (measured in volts) by the current passing through the appliance (measured in amperes) to obtain the power (measured in watts). The voltage drop across the appliance indicates how much energy the appliance extracts from each unit of charge pass through it and the current passing through the appliance is the measure of how many units of charge are passing through the appliance each second. Thus the product of voltage drop times current gives the energy that the appliance extracts from the current each second, which is the power extracted by the appliance. On the other hand, if the appliance behaves like an inductor or capacitor--meaning that the current passing through it isn't proportional to the voltage drop across it--it's much harder to calculate the power that the appliance is consuming.

An electric welder sends an electric current through an ionized gas, forming a pattern of current flow through the gas that is known as an arc. The ionized gases in this arc consist of electrons that are negatively charged and atoms or molecules that have lost electrons to become positively charged. The electrons flow toward the positively charged metal at one end of the arc while the positively charged ion flow toward the negatively charged metal at the other end of the arc. As these charged particles move, they collide frequently with one another and with gas atoms or molecules along their paths, and they convert some of their electric energies into thermal energy. These collisions also produce additional ions. The enormous amounts of thermal energy produced by collisions as the charged particles flow through the arc melts the metals at the ends of the arc so that these metals can be fused together.

When you send an alternating current through the primary coil of wire in a transformer, that current produces a magnetic field in the transformer. Because the current in the primary coil is changing with time--it's an alternating current--this magnetic field is changing and changing magnetic fields are accompanied by electric fields. In the transformer, this electric field pushes electric charges around the secondary coil of wire in the transformer. Since these electric charges are pushed in the direction they are traveling, work is being done on them and their energies are increasing. However, in the transformer you mention, the secondary coil of wire has fewer turns in it that the primary coil of wire. As a result, the charges don't receive as much energy per charge (as much voltage) as the charges in the primary coil are giving up. This type of transformer, in which the secondary coil has fewer turns of wire than the primary coil, is called a step-down transformer and reduces the voltage of an alternating current.

Any rechargeable battery will do for this job, although I'd recommend using a lead-acid battery. To charge it, you need a wind-powered DC generator. You can make such a generator by attaching a DC motor to the blades of a fan and providing some weather-vane mechanism to ensure that the fan always points into the wind. The wind will then cause the fan to spin, and with it the motor. Wind energy will become mechanical energy and that will in turn become electric energy. The DC motor will act as a generator and will produce electric power.

To make this generator recharge the battery, you first need to ensure that the motor can generate a voltage that's at least 20% higher than the voltage of the battery while the wind is blowing at its usual rate. If it can't, you need a higher voltage motor or a lower voltage battery. Now you should connect the negative output wire of the generator to the negative terminal of the battery and use a power rectifier (a power diode) to connect the positive output wire of the generator to the positive terminal of the battery. You need this diode to prevent the battery from sending its power into the motor and making the fan turn when the wind isn't blowing hard. If the fan starts turning when you've inserted the diode, you have it installed backward. When correctly inserted, the diode will prevent the battery from operating the fan so that the fan can only charge the battery. When the wind starts blowing and the fan starts turning, it will charge the battery.

The electricity you receive comes from a distant power plant. A generator in that power plant produces a substantial electric current of medium high voltage electric charge. This current is alternating, meaning that its direction of flow reverses many times a second--120 reversals per second or 60 full cycles of reversal (over and back) in the United States. This alternating electric current flows through the primary coil of wire in a huge transformer at the power plant, where it produces an intense alternating magnetic field. When a magnetic field changes with time, it produces an electric field and, in the transformer, this electric field pushes electric charges around a second coil of wire in the transformer, the secondary coil. The effect of this transformer is to transfer power from the current in the primary coil of the transformer to the current in the secondary coil of the transformer. Thus the generator's electric power moves along to the current passing through the secondary coil of the transformer. However, the secondary coil has far more turns of wire than the primary coil and this gives each charge passing through that coil far more energy than the charges had in the primary coil. Although the current passing through that secondary coil is relatively small, it acquires an enormous voltage by the time it leaves the secondary coil. The transformer has produced this high voltage power needed for efficient power transmission to a distant city.

This high voltage electric current passes through the countryside on high voltage transmission wires. The value of using a small current of high voltage charges is that wires waste power in proportion to the square of the electric current they are carrying. Since the current in the transmission wires is small, they waste relatively little power.

When this current reaches your town, it passes through a second transformer, which transfers its power to yet another electric current. This current is large and, because it passes through a coil that has few turns of wire, it acquires only a medium high voltage when it flows through the secondary coil of the new transformer. Electricity from this second transformer flows toward your neighborhood through medium high voltage wires. Finally, near your home there is a third and final transformer that extracts power from the medium high voltage current and transfers that power to a very large current that acquires a low voltage when it flows through the secondary coil of the final transformer. It is this very large current of low voltage charges that flows through appliances in your home and those of your neighbors. That final transformer is often visible as a large gray drum on a utility pole or a green box in someone's yard.

As in any photoelectric cell, the energy from a single particle of light--a photon--is used to raise the energy of an electron in a diode and to propel that electron from one side of the diode to the other. In this process, the light energy is partly converted to electrostatic potential energy and partly to thermal energy. Since a diode only carries current in one direction, the electron is unable to return to its original side. In a photoelectric cell, the electron flows through a circuit to return to the other side of the diode and provides energy to that circuit. In a charge coupled device, a complicated charge shifting system transfers the electrons to a detector that registers how much light was absorbed.

The genius of George Westinghouse and Nikola Tesla in the late 1800's was to realize that producing alternating current made it possible to transfer power easily from one electric circuit to another with the help of an electromagnetic device called a transformer. When an alternating electric current passes through the primary wire coil of a transformer, the changing magnetic and electric fields that this current produces transfer power from that primary current to the current passing through another coil of wire--the secondary coil of the transformer. While no electric charges move between these two wires, electric power does. With the help of a transformer, it's possible for a generating plant to move power from a large current of relatively low energy electric charges--low voltage charges--to a small current of relatively high-energy electric charges--high voltage charges. This small current of high voltage electric charges can move with relatively little power loss through miles and miles of high voltage transmission lines and can go from the generating plant to a distant city without wasting much power. Upon arrival at the city, this current can pass through the primary coil of another transformer and its power can be transferred to a large current of relatively low voltage charges flowing through the secondary coil of that transformer. The latter current can then deliver this electric power to your neighborhood. A transformer can't transfer power between two circuits if those circuits operate with direct current. Edison tried to use direct current in his power delivery systems and fought Westinghouse and Tesla tooth and nail for years. Edison even invented the electric chair to "prove" that alternating current was much more dangerous than direct current. Still, Westinghouse and Tesla won out in the end because they had the better idea.

Although I have never done it myself, I understand that it is possible to run electric power directly from the power line through a hot dog and to use the resistive heating that occurs as electric current struggles to pass through the hot dog to cook that hot dog. While I can't recommend doing this and caution anyone trying it to be extremely careful with the electricity (i.e. seek adult supervision from someone who is experienced with the safe handling of electricity), I believe that it can be done. My understanding is that you should carefully connect each wire of an electric power cord (unplugged!) to its own nail (choose an uncoated steel nail to avoid toxic materials). You should then insert one nails into each end of the hot dog and place that hot dog on a safe, nonconducting surface where no one and nothing can touch it. Finally, you should plug the electric cord into an electric socket that is properly connected to a working circuit breaker. I would recommend using a socket protected by a ground-fault interrupter (GFI) such as are used in modern bathrooms (the ones with a "test" and "reset" button). (As you can see, I don't want anyone hurt!) I'm not sure how quickly the hot dog will cook, but I'd expect it to be quite fast. Be sure to unplug the cord before getting anywhere near the hot dog.

In most situations of AC electric power generation or AC electric power consumption, the current flowing through the circuit is in phase with (or, more simply, directly proportional to) the voltage across the circuit. But that isn't always the case. In situations involving reactive components (e.g., capacitors and inductors), it's possible for the current and voltage to be out of phase with one another. If the current and voltage are a full 90° out of phase, there is no average power flowing through the circuit. I believe that VAR is a reference to this portion electricity in the circuit--the portion for which the voltage and current are 90° out of phase. While this portion of the electricity doesn't transfer any power, it does place demands on the power transmission system. I think that the distinctions between "importing" and "exporting" and between "consuming" and "producing" are related to the phase ordering of the current and voltage (whether a device is acting as a capacitor or an inductor). In one case, the voltage leads the current by 90° and in the other the current leads the voltage by 90°.

Lightning tends to strike elevated objects that acquire large charges that are opposite to those of the clouds. Since transformers are often elevated and they are connected to wires that allow them to become highly polarized when a charged cloud passes overhead, transformers are good targets for lightning.

It's probably fine. While the high-tension wires do create modest alternating electric and magnetic fields, there is no credible evidence that these fields cause any injury and no one has proposed a convincing mechanism whereby those fields could affect biological tissue.

Your skin is a very good electric insulator and it prevents any current from passing through your body as long as that current doesn't have much voltage. A higher voltage (the electric equivalent of "pressure") is required to push charge through your skin. But once the charge is inside you body, it moves through you quite easily--your body fluids are essentially salt solutions and are relatively good conductors of electricity.

However, a small current passing through your body won't cause injury. It takes about 0.030 amperes or 30 milliamperes to cause a life-threatening disturbance to your "electric system." The small currents associated with static electricity are not enough to cause trouble, even through they easily pass through your skin. So high voltages are needed to break through your protective barrier--your skin--in order to give you a shock, but large currents are needed to injury you.

A metal's conductivity is related to how far an electron can coast through the metal before suffering a collision that reduces its kinetic energy. Since an electron can collide with an impurity in the metal or a region of local disorder, the first task in obtaining a good conductor is to make a pure and uniform metal. Increased temperature also enhances these inelastic collisions, so keeping a metal cool improves its conductivity. Finally, different metals exhibit different couplings between the electrons and the metal ions from which those electrons came. Copper and aluminum have relatively weak electron-ion couplings while steel and lead have stronger couplings. The stronger the coupling, the more likely is a collision between an electron and an ion. Because of their weaker couplings, the electrons in copper and aluminum suffer far fewer collisions per centimeter than the electrons in steel and lead. That's why copper and aluminum are better conductors of electricity than steel and lead. The coupling in copper is only slightly weaker than that in aluminum, so they have similar conductivities. However, aluminum's tendency to form a very hard, insulating oxide coating (aluminum oxide or "alumina" is the mineral sapphire) makes it a bit tricky to use in wiring.

kVA is the product of kilovolts (kV) times amperes (A) and is a measure of power. In fact, if you multiply the voltage in volts delivered to an electric heater by the current in amperes sent through that heater, you will obtain the electric power in watts consumed by the heater. Thus the heater's power consumption in watts is the same as the product of its voltage times its current, or its kVA. However, there are many devices that don't behave like an electric heater. The heater is purely resistive, while many other devices such as motors are both resistive and reactive. Reactive devices don't obey Ohm's law and may not draw their peak currents at times of peak voltage. Therefore, the power in watts consumed by a reactive device isn't the same as the product of its current times its voltage, or its kVA.

Most homes receive power through three wires: two power wires and one neutral wire. Each power wire is at 120 volts AC with respect to the neutral wire, meaning that its electric potential fluctuates up and down with respect to the neutral wire and behaves as though, on average, it were 120 volts away from the potential of the neutral wire. But the fluctuations of the two power wires are opposite one another--when one power wire is at a positive voltage relative to the neutral wire, the other power wire is at a negative voltage relative to the neutral wire. If you compare the two power wires to one another, you'll find that they behave as though, on average, they are 240 volts away from one another. Thus home appliances that need 240 volts are powered by the two power wires, rather than one power wire and one neutral wire.

Electronic dimmers do clip the AC cycle. They use transistor-like devices called triacs to switch on the current to a lamp part way into each half-cycle. By shortening the time that power is delivered to the lamp, the dimmer reduces the total energy delivered to the lamp during each half-cycle and the lamp dims. But while a triac turns on easily, the only way to turn it off is to get rid of any voltage drop across it. The dimmer uses the alternating current itself to turn off the triac--the voltage of the power line naturally goes to zero at the end of each half-cycle and the triac turns off. The triac then waits until the dimmer restarts it, sometime into the next half-cycle.

Since the dimmer messes up the waveform of the electric current flowing through the lamp circuit, what you measure with a voltage meter depends on how that meter works. Since many AC voltmeters just measure peak voltage and assume that they are looking at a pure sinusoidal current, they don't give you an accurate sense for what is really happening to the voltage of this clipped waveform as a function of time. Unless an electronic dimmer is turned way down, the peak voltage it delivers will be close to the normal power line peak, a fact which tricks the voltage meter into reading a high value and which allows a properly designed fluorescent lamp to continue operating normally but at a dimmer level.

Electricity typically costs about 7 cents per kilowatt-hour. Over the course of an hour, a 100-watt light bulb will use 100 watt-hours or 0.1 kilowatt-hours, at a cost of about 0.7 cents. That's about 0.012 cents per minute.

The generating station uses a large generator to transfer energy from a giant turbine to an electric current flowing through a coil of wire. Current from this generating coil then flows through the primary coil of a huge transformer, where it transfers its energy to the magnetic core of the transformer. The current then returns to the generator to obtain more energy.

The magnetic core of the transformer transfers its energy to a second current--one that is passing through the secondary coil of the transformer. Because this current consists of far fewer electric charges per second, each charge receives a very large amount of energy. This large energy per charge gives the current a high voltage and it flows very easily through a high voltage transmission line. Because the amount of power that a wire loses is proportional to the square of the current passing through it, this high-voltage, low-current electricity wastes very little power in the transmission line on its way across country to your city. When the current reaches your city, it passes through another transformer and its energy is transferred to a third current. The cross country current then returns through the transmission line to the original power station to obtain more energy from the first transformer.

This third current involves more charges per second, so each charge carries less energy and the voltage is lower. This medium voltage electricity travels to your neighborhood before passing through a final transformer. This final transformer is probably either a gray metal can on a utility pole or a green box on a nearby lawn. In passing through the final transformer, the current transfers its energy to a current which then enters your home. This last current delivers energy to your appliances and lights and then returns to the final transformer to obtain more energy.

The electromagnetic fields (EMF) produced by the currents in an electric blanket are very weak and it takes a pretty sensitive electronic device to detect them. You body is not nearly so sensitive and I still haven't seen any credible explanation for how these fields could cause any injury to biological tissue. I strongly suspect that all the concern about EMF is just hysteria brought about by a few epidemiological flukes or mistakes.

Yes. Tesla found that the alternating electromagnetic fields around a large high frequency transformer could propel currents through wires or lamps that were located at a moderate distance from the transformer. But this technique of using the alternating fields near a transformer to provide power aren't very practical--there is too much power wasted through radiation or in heating things that aren't meant to be heated.

Probably not very dangerous. The radiation itself is so weak that it can't cause significant heating in your body (as the microwaves used in diathermy treatment do) and so low frequency that it can't do chemical damage (as the X-rays from a CT scan do). The only possible source of trouble is the small electric and magnetic fields from the power lines and there is still no credible evidence that these affect biological tissue. Moreover, there are sound physical arguments why those fields should not be able to affect biological tissue. Only in rare cases of an organ that is devoted to sensing magnetic fields (e.g., in migratory birds) is there any reasonable interaction between tissue and small magnetic fields.

That depends on the electricity's voltage. The transmission lines carrying the electricity are important parts of the overall electric circuit. They waste electric power as they carry current and the amount of power they waste is proportional to the square of the current they carry. The purpose of high voltage transmission lines is to send as small a current as possible across the countryside so that the wires waste as little power as possible. This reduction in current is possible if each electric charge moving in that current carries a large amount of energy--the current must be one that consists of high voltage charges. In short, higher voltage transmission lines employ smaller currents and waste less power than lower voltage transmission lines.

When Thomas Edison set out to electrify New York City, he used direct current of the highest practical household voltage. Nonetheless, his relatively low voltage power transmission lines wasted so much power that he had to scatter generating plants throughout the city so that no home was far from a power plant. But when George Westinghouse and Nicola Tesla realized that using alternating current and transformers to temporarily convert the household power to high voltages and small currents, they were able to send power long distances without wasting electricity. That realization eventually destroyed Edison's direct current electric system and gave us the modern alternating current system. It's now common to send electric power several hundred miles through high voltage transmission lines. At those distances, perhaps half the power is lost en route. I doubt that transmission of power more than 1,000 miles is practical.

A Tesla coil is radio-frequency transformer that produces small currents of very high-energy electric charges. A radio frequency alternating current passes through the primary coil of this transformer and it induces a current in the secondary coil of the transformer. The frequency of the alternating current must be extremely high because there is no iron in the core of the transformer to store energy during a cycle, so that each cycle must be very brief. Because the alternating current flowing out of the secondary coil of the transformer has a very high frequency, it travels over the surface of a conductor, rather than through its center. Thus when you allow that current to pass through you, it goes along your skin and not through your body. As a result, you barely feel its passage except perhaps as surface heating (however, it can cause what is called an "RF burn" in some cases.) Also, the current from a typical Tesla coil is very small so it would barely be noticeable even if it went through your body.

Although I haven't been able to find detailed lists of the magnetic fields near common appliances (such lists do exist), those fields are unlikely to be stronger than the earth's own magnetic field. That's because the magnetic fields in most appliances are created by electric currents and you must be quite near a relatively large current before the magnetic field of that current exceeds 0.5 gauss, the strength of the earth's magnetic field. But while an appliance's magnetic field is likely to be no greater than that of the earth, the appliance's magnetic field does change with time. It reverses each time that the alternating current from the power line reverses. In the United States, that's 120 reversals per second (60 full cycles of reversal, over and back, each second).

The watt is the standard unit of power--that is, it's the way in which we measure how much energy is being transferred to or from sometime each second. 1 watt is equivalent to 1 joule of energy per second. A 100 watt light bulb consumes 100 joules of electric energy each second. Anytime energy moves from one place to another, you can determine how much power is flowing. For example, the food energy in a jelly donut is about 1 million joules, so if you eat 1 jelly donut in 100 seconds, you receive 10,000 watts of power. Since your body only consumes about 100 watts of power while you are resting, it will take you 10,000 seconds to use up all that food energy.

The amp (or ampere) is the standard unit of electric current--that is, its the way in which we measure how many electric charges flow past a certain point each second. 1 amp is equivalent to 1 coulomb of electric charge per second. Since 1 coulomb of electric charge is the charge on 6,240,000,000,000,000,000 protons, even a current of only 1 amp means that a great many electric charges are passing each second. The current passing through a 100-watt light bulb is roughly 1 amp on average, while the current used in starting a car is about 100 amps.

Electric power is distributed over long distance using high voltages and relatively low currents. Since the amount of power that flows through a wire is equal to the product of its voltage (the amount of energy carried by each unit of electric charge) and its current (the number of units of electric charge that flow through the wire each second), the electric company can distribute its power either as a large current at low voltages or a small current at high voltages. But it turns out that the amount of power that's wasted by electricity as it flows through a wire is proportional to the square of the current in that wire. Thus the more current that flows through a wire, the more power that wire turns into thermal energy (or heat). To minimize this energy loss, the power company uses transformers to convert the electricity to small currents at very high voltages for transmission cross country. Near each community, there is then a power substation at which this very high voltage power is converted to lower voltage forms. Even in neighborhoods, they use medium currents at moderately high voltages to avoid power wastage. Only in the vicinity of your home is the electricity finally converted by transformers to a large current at low voltage for safe delivery to your appliances. You've probably seen those final transformers as the gray oil-drum sized units on utility poles or the green boxes on front lawns. But despite all this effort to minimize power loss, something like 6% of the electric power generated in this country is lost in the delivery process.

It depends on the situation. You cannot use a transformer with direct current, so in that sense, alternating current is better. But many electronic devices need direct current because they require a steady flow of charges that always head in the same direction. So there are times when you need DC and times when you need AC.

Wires obey Ohm's law: the current flowing through them is proportional to the voltage drop across them. But the precise relationship depends on the wire's length. A short wire will carry a large current even when the voltage drop across it is small because that wire has a small electrical resistance; it does not impede the flow of electricity very much. But a long wire has a large electrical resistance and will only carry a large current if the voltage drop across it is large. If you do not change the source of electrical power (e.g. a battery) and replace short wires with long wires, those wires will not be able to carry as much current.

High voltages involve large accumulations of like electric charges. These charges repel one another ferociously and can leap off into the air near sharp points and edges. They produce sparks and corona discharges. While these discharges are useful in some devices (e.g. copiers and air cleaners), they tend to transfer energy to air molecules and can break up those air molecules. When normal oxygen molecules (which each contain 2 oxygen atoms) break up, the resulting oxygen atoms can stick to other oxygen molecules to form ozone molecules (which each contain 3 oxygen atoms). That is why you can often smell ozone near electrical discharges, high voltage power lines, and after thunderstorms.

Only electromagnets can change back and forth and then only when they are connected to a supply of alternating current. A permanent magnet, such as that used to hold notes to a refrigerator, has permanent poles that do not change. But an AC powered electromagnet, such as that found in a transformer, does have poles that change back and forth.

Your body is a relatively good conductor of electricity and it is easily damaged by currents flowing through it. Your body uses electricity to control its functions and an unexpected current of as little as a few hundredths of an ampere can interrupt those functions. In particular, your heart can stop beating properly. Fortunately, your skin is a pretty good insulator so it is hard to get any current to flow through you. But high voltages can push current so hard that it punctures your skin and begins to flow through you. While the current is actually what injures you, the high voltage is what breaks down your protective skin and allows that current to flow through you.

The reversal of the current in an alternating current (AC) circuit occurs everywhere in the circuit at once. The whole current gradually slows to a stop and then heads backward. At the moment it comes to a complete stop, the electric power company isn't supplying any power at all and the circuit isn't consuming any. Because the power delivery pulses on and off in this manner, devices that operate on AC power are designed to store energy between reversals. Motors store their energy as rotational motion. Stereos store energy as separated electric charge in devices called capacitors, or as magnetic fields in devices called inductors.

A transformer involves two completely separate circuits: a primary circuit and a secondary circuit. Charges circulate within each circuit, but do not move from one circuit to the other. If the primary circuit of a transformer has a small current flowing through it and that current experiences a large voltage drop as it flows through the transformer's primary coil, then the primary circuit current is transferring power to the transformer and that power is equal to the product of the primary circuit current times the voltage drop. The transformer transfers this power to the current flowing in the secondary circuit, which is an entirely separate current. That current may be quite large, in which case each charge only receives a modest amount of energy as it passes through the secondary coil. As a result, the voltage rise across the secondary coil is relatively small. The power the transformer is transferring to the secondary circuit current is equal to the product of the secondary circuit current times the voltage rise.

Yes. If you use higher voltages, you can transfer the same amount of power with a small current of charged particles. The energy lost in the transmission through wires increases as the square of the amount of current through those wires so reducing that current is very important.

The pump for alternating current (usually an electrical generator) creates electric fields that reverse their directions 120 times a second (60 full cycles of reversal, over and back, each second). This reversal pushes the current backward and forward through the wires connecting to this power source. The currents direction of flow alternates and so does its voltage.

The iron core of a transformer stores energy as power is being transferred from the primary circuit to the secondary circuit. This energy is stored as the magnetization of that iron. The transformer needs to store that energy for roughly one half cycle of the alternating current or about 1/120th of a second. The more iron there is in the transformer, the more energy it can store and the more power the transformer can transfer from the primary circuit to the secondary circuit. Without any iron, the energy must be stored directly in empty space, again as a magnetization. But space isn't as good at storing magnetic energy as iron is so the iron increases the power-handling capacity of a transformer. Without the iron, the transformer must operate at much higher frequencies of alternating current in order to transfer reasonable amounts of power.

The electric currents in those lines are reversing 120 times a second in the United States (60 full cycles of reversal, over and back, each second). That means that the electrostatic forces between the charges they carry and anything nearby reverse 120 time a second and the magnetic forces that they exert on one another when currents flow through them turn on and off as well. You hear all of the motions that are caused by the pulsating electric and magnetic forces.

In the 2 prong system, current travels to the appliance through one prong and leaves through the other prong. The roles of the two prongs interchange every 120th of a second. In the 3-prong system, there is one extra prong and that connects the frame of the appliance to the ground (the earth). This extra connection is a safety feature. If a wire comes loose inside the appliance and touches the frame, the frame can deliver charge and current to you through your hand and you can deliver it to the ground through your feet or your other hand. The earth is very large and a large amount of charge can flow into it without repelling further charge. Moreover most electrical systems are actually connected to the ground at some point. So if current can travel out of the circuit feeding power to the appliance and travel through you and into the ground, it will. You'll get a shock. The ground connection (the extra prong) allows this extra current to flow to ground so easily that a huge current is drawn out of the power source, causing the fuse or circuit breaker in that power source to break the connection. When that power connection is broken, no power can flow to the appliance at all and you can't get a shock from it. Plastic appliances often omit the extra prong because they have nothing dangerous to touch on their exteriors.

In single-phase power, current flows to and from a device through a pair of wires. The direction of the current flow changes with time, reversing smoothly 120 times a second in the US or 100 times a second in Europe (60 or 50 full cycles of reversal, over and back, each second respectively). In its simplest form, one of the two wires is called "neutral" and its voltage is always close to 0 volts (meaning that it has essentially no net electric charge on it). The other wire is called "power" and its voltage fluctuates from positive to negative to positive many times a second (meaning that its net electric charge varies from positive to negative to positive). The difference in voltage between "neutral" and "power" propels current through the device.

In three-phase power, current flows to and from a device through a group of three wires. These three wires are often called "X", "Y", and "Z", and each one is a power wire with a voltage that fluctuates from positive to negative to positive many times a second. (A fourth wire, "neutral", with a voltage of approximately 0 volts, may also be used.) But while the voltages of the three power wires fluctuate up and down the same number of times each second, they do not reach their maximum or minimum voltages at the same time. They reach their peaks one after the next in an equally spaced sequence: first "X", then "Y", then "Z", and then "X" again and so on. Because these three wires or "phases" rarely have the same voltages, currents can and do flow between any pair of them. It is such current flows that power the devices that use three-phase electric power. The natural sequencing of the three phases is particularly useful for devices that perform rhythmic tasks. For example, three-phase electric motors often turn in near synchrony with the rising and falling voltages of the phases.

Another advantage of three-phase electric power is that there is never a time when all three phases are at the same voltage. In single-phase power, whenever the two phases have the same voltage there is temporarily no electric power available. That's why single-phase electric devices must store energy to carry them over those dry spells. However, in three-phase power, a device can always obtain power from at least one pair of phases.

Current is the measure of how many charges are flowing through a wire each second. A 1-ampere current involves the movement of 1 Coulomb of charge (6,250,000,000,000,000,000 elementary charges) per second. Voltage is the measure of how much energy each charge has. A 1-volt charge carries 1 Joule of energy per Coulomb of charge. To use water in a pipe as an analogy, current measures the amount of water flowing through the pipe and voltage measures the pressure (or energy per liter) of that water.

Resistance is the measure of how much an object impedes the flow of electricity. The higher an object's resistance, the less current will flow through it when you expose it to a particular voltage drop. To use the water analogy, resistance resembles a constriction in a pipe. The narrower the pipe (higher the resistance), the harder it is to push water through that pipe. If you keep the water pressure constant (constant voltage drop) as you narrow the pipes (increase the resistance), then less water will flow (the current will drop).

When current flows through a battery or the secondary of a transformer, its receives power. Each charge leaves the battery with more energy than it had when it arrived. Since the energy of each charge has increased, the voltage (energy per charge) of the current has increased. Thus the current passing through the battery experiences a rise in voltage or a "voltage rise".

Thin wires or wires made of poor conductors. Some metals are simply better at carrying current without wasting energy than other metals. It has to do with how often a charge bounces off of a metal atom and loses energy. Copper, Silver, and Aluminum are good conductors while stainless steel and lead are pour conductors. Metals tend to become better conductors as you cool them and worse as you heat them. Semiconductors such as carbon (graphite) are poor conductors but have the reverse temperature effect. At low temperature they are poor conductors but become good conductors at high temperature.

A Joule is a unit of energy; the capacity to do work. A Coulomb is a quantity of electric charge; equal to about 6,250,000,000,000,000,000 elementary charges. An Ampere is a measure of current; equal to the passage of 1 Coulomb of charge each second. A Volt is a measure of the energy carried by each charge; equal to 1 Joule of energy per Coulomb of charge. A Watt is a measure of power; equal to 1 Joule per second. A current of 1 Ampere at a voltage of 1 Volt carries a power of 1 Watt. That is because each Coulomb of charge carries 1 Joule of energy (1 Volt) and there is 1 Coulomb of charge moving by each second (1 Ampere). That makes for 1 Joule of energy flowing each second (1 Watt).

Yes. When you try to push current through a wire, the voltage drop across that wire (i.e. the energy lost by each charge passing through that wire) is proportional to the number of charges flowing through that wire each second (i.e. the current through the wire). If you double the number of charges flowing through the wire each second, then each charge will lose twice as much energy (the voltage drop across the wire will double). If you halve the number of charges flowing through the wire each second, then each charge will lose half as much energy (the voltage drop across the wire will halve).

The transformer moves power from the primary circuit to the secondary circuit, almost without waste. The main reason for using a transformer is to change the relationship between voltage and current. Whenever you need a large current of low energy, low voltage charges, you probably want a step-down transformer. Whenever you need a small current of high energy, high voltage charges, you probably want a step-up transformer. I have already described the issues in power distribution, but transformers are used in many other devices. Step-down transformers are used to power small electronic devices instead of batteries (those little black boxes you plug into the wall socket contain transformers and some electronics to convert the resulting low voltage AC into low voltage DC). Step-up transformers are used in neon signs and bug-zappers.

Your first observation, that high current times low voltage would equal low current times high voltage is true; it means that electricity can deliver the same power in two different ways: as a large current of low energy charges or as a small current of high energy charges. That result is critical to the electrical power distribution system. The resistance problem is a side issue: it makes the delivery of power as a large current of low energy charges difficult. If you could get this current to peoples' houses without wasting its power, there would be no problem, but that delivery isn't easy. The wires waste lots of power when you try to deliver these large currents. So the electric power distribution system uses small currents of high-energy charges instead.

Usually with alternating current generators, which we will discuss next. It can also be made by electronic alternators, such as those found in the uninterruptible power supplies that provide backups for computers.

These devices use diodes, which are one-way devices for current. They only allow the current to flow a certain direction and block its flow the other way. With the help of some charge storage devices called capacitors, these diodes can stop the reversals of AC and turn it into DC. Those little black battery eliminators that you use for household electronic devices contain a transformer, a few diodes and a capacitor or two.

A step-up transformer has a secondary coil with many, many turns. As the current in the primary circuit flows back and forth, it creates a reversing electric field around the iron core of the transformer. This electric field pushes charges through the secondary coil so that it travels around and around the core. Each charge goes around many times, picking up more energy with each passage. By the time the charge leaves the transformer, it has lots of energy so its voltage is very high.

The voltage is stepped up at the power plant so that a small current of very high voltage charges (high energy per charge) can carry enormous power across the countryside. When this current arrives at your city, its voltage is stepped down so that a medium current of medium high voltage charges can carry that same enormous power through your city. Finally, near your house, its voltage is again stepped down so that a large current of low voltage charges can carry this power into your house. Naturally, you do not use all of the power from the power plant yourself, so it is distributed among all of the buildings in the city.

Hydroelectric power begins with water descending from an elevated reservoir, such as a lake in the mountains. While it's in the elevated reservoir, this water has stored energy--in the form of gravitational potential energy. As this water flows downward through a pipe, its gravitational potential energy becomes either kinetic energy or pressure potential energy or both. By the time the water arrives at the hydroelectric power plant, it is either traveling very quickly or has an enormous pressure or both. In the power plant, the water flows past the blades of a huge turbine and does work on those blades. The blades are shaped somewhat like airplane wings and they "fly" through the moving water. Since the blades are attached to a central hub, they cause this hub to rotate and allow it to turn the rotor of a huge electric generator. The rotor of this generator typically contains a giant electromagnet. The electromagnet turns within a collection of stationary wire coils and it induces electric currents in those coils. These electric currents carry power out of the generator to the homes or business that need it.

The fiction of current being carried by positive charges really does work nicely. If a wire is carrying negatively charged electrons to the east, then the east end of the wire is becoming more and more negative and the west end is becoming more and more positive. The same would happen if that wire were carrying positively charged particles to the west. Even though these positively charged particles aren't really there, we can pretend that they are. By pretending that current is carried by positive particles, we don't have to worry about the arrival of a positive number of negatively charged electrons lowering the voltage of an object.

Sometimes lightning strikes a power line and deposits a large amount of charge on it. This charge has considerable electrostatic potential energy so its voltage is very large (a large positive voltage if the lightning carried positive charge, a large negative voltage if the lightning carried negative charge). A the charge flows outward along the wires, it raises the local voltages of the wires. This sudden, brief increase in the local voltages is what you mean by a power surge. Many devices (e.g. computers and televisions) can be damaged by such a surge in voltage. Even a light bulb can be damaged because the extra voltage pushes too much current through the filament and can burn it out.