Category: electric power generation

How can you make electricity with magnets? – AL

You can make electricity by moving a magnet past a wire. The magnet has a magnetic field around it—something that exerts forces on magnetic poles. If you move the magnet and its magnetic field, you create an electric field—something that exerts forces on electric charges. That’s because whenever a magnetic field changes with time, it creates an electric field. This electric field will push on the mobile electrons in a wire. So when you move a magnet past a wire, you are producing a changing magnetic field in the wire. This changing magnetic field produces an electric field and the electric field makes the electrons in the wire accelerate. The moving electrons are electricity. Generators move magnets past wires (or wires past magnets) to produce electricity.

How does an internal voltage regulator type auto alternator work and are they any better than an external regulator type? – H

An alternator is a device that uses rotary motion to generate electricity. As the car engine turns, it spins a magnet (the rotor) in the alternator and this spinning magnet induces electric currents in a set of stationary wire coils (the stator). The alternator’s ability to generate electric currents by spinning a magnet past stationary wires is an example of electromagnetic induction. Induction is a general phenomenon in which a moving or changing magnetic field creates an electric field, which in turn pushes electric charges through a conducting material. Overall, some of the engine’s mechanical energy is converted into electric energy.

The amount of energy given to each electric charge that flows through the wires in the stator depends on the speed with which the magnet turns and the strength of that magnet. Whether it’s internal or external, the voltage regulator monitors this energy per charge—also known as the voltage—to make sure that it’s correct. If not, it adjusts the strength of the alternator’s magnet. It can do this because the alternator’s magnet is actually an electromagnet and its strength depends on how much current is flowing through its wire coils. The voltage regulator carefully adjusts the current flowing through the electromagnet in order to obtain the proper output voltage from the alternator. Actually, the alternator itself produces alternating current, so a set of solid-state diodes converts this alternating current into direct current. A car’s electric system, particularly its battery, operates on direct current. Since the alternator’s operation is the same whether the voltage regulator is inside it or external to it, neither version should be better than the other.

How does waterpower work? – MA

By “waterpower” I assume that you mean hydroelectric power. In that case, water from an elevated source enters a pipe and travels downhill to a generating plant. As the water descends, its gravitational potential energy (the stored energy associated with height and the earth’s gravity) becomes pressure potential energy (the stored energy associated with pressure) and kinetic energy (the energy of motion). By the time the water reaches the generating plant, it has enormous pressure and a modest speed.

This moving, high-pressure water is then sent through a fan-like turbine. As the water moves toward the low pressure beyond the turbine, it does work on the turbine’s rotating blades and its energy is transferred to those blades. The water gives up its energy and the turbine takes away this energy in its rotary motion. The turbine is attached to an electric generator, which uses moving magnets and wire coils to turn the turbine’s rotary energy into electric energy. The electric energy is carried away on wire to be used elsewhere. Overall, the water’s gravitational potential energy has become electric energy.

Can you get electricity or some sort of energy or power from fruit? — J, Embrun, Ontario

The answer is yes, but the method may not be what you had in mind. While it’s possible to make a battery by inserting two dissimilar metal strips into the fruit, the battery that results is really powered by the metals themselves. The fruit juice just acts as an “electrolyte”—an electrically conductive liquid that facilitates the movement of electric charges. Claiming that the fruit is responsible for the energy is like claiming that the stone in “stone soup” (an old tale about a beggar who tricks the villagers in a community into contributing vegetables to spice up the soup that he’s making with his magic stone) is really the basis for the soup.

The best way to obtain energy from the fruit is to eat it! The sugars and starches in the fruit have plenty of chemical potential energy that’s released when those chemicals are oxidized in your body. This released energy is what allows you to live, work, and play.

How efficient are solar energy cells and windmills in producing energy for everyday use? — JJ, San Antonio, TX

There are several ways to measure their efficiencies. One way is to compare the energy these devices extract from sunlight or from the wind to the electric energy they produce. By that measure, solar cells are roughly 15% efficient and windmills are roughly 50% efficient. However, you’re probably most interested in their cost efficiency—in how much power these devices can produce for a given operating cost. By that measure, both devices are somewhat more expensive to build and operate than conventional fossil-fuel power plants. As a result, the United States continues to rely on fossil-fuel plants because they cost less for each kilowatt-hour of electric energy produced. Nonetheless, solar cells are gradually becoming cheaper and they may become cost effective in the next decade or two. Windmills are already cost effective in some countries that rely entirely on imported fossil fuels. Denmark, for example, uses windmills extensively for electric power. While windmill power plants do exist in the United States, they are largely the results of regulation rather than market forces. But that, too, may change in the next decade or two.

If you connect two direct current motors so that the current flowing through one also flows through the other, then turning one motor will cause the other motor to turn as well. If you reverse the direction of rotation, the other motor will also reverse its direction of rotation. Why does this happen?

DC motors turn in a direction that depends on the direction of that current. If you reverse the direction of current flowing through the motor, its direction reverses, too. When you use one DC motors as a generator, it produces DC current! The direction of that current depends on which way you turn the motor. Thus as you turn the first motor clockwise, it generates current in a particular direction through the circuit connecting the two motors and the second motor also turns clockwise. If you then reverse the first motor, the current in the circuit reverses and so does the second motor.

What happens to the current when it “stops”?

Current refers to moving charged particles. In most solids, the particles that do the moving are negatively charged electrons that move in the opposite direction from the way we say that current is flowing. These charged particles are the components of atoms and molecules, so they are always there inside a wire or the filament of a light bulb, even if they are not moving. Thus when the current “stops”, these electrically charged particles simply stop moving. You can imagine a pipe full of water. The water can be flowing to the right or left (a current) or it can be standing still (no current). The water itself, like the charged particles, doesn’t disappear when the flow stops.

When flashbulbs were used with cameras, was there a coil in the camera and a magnet, or how did they get it to light? Also, how are flashes used on cameras today different than flashbulbs?

Flashbulbs contain a wad of very fine magnesium wire that burns almost instantly in a gas of pure oxygen. The wire is ignited by a small piece of gunpowder-like primer material that is itself ignited by the camera. There are/were three techniques for igniting the primer: impact (a little lever smacked the side of a tube containing the primer and it burst into flame, just like a cap), electric current (a thin filament inside the bulb overheated when current ran through it), and spark (a spark jumped between two wires and ignited the primer). A camera that uses/used the current-ignited bulbs has a battery in it and taking a picture closes a circuit that then sends current through the bulb. A camera that uses/used the spark-ignited bulbs used a piezoelectric spark igniter, like the ones in outdoor gas grills. A camera that uses/used the impact-ignited bulbs just hit the primer itself. Modern cameras uses gas discharges to produce light. Since the flashlamp isn’t burned up during a flash, it can be used many times.

Why does a moving magnet excite charges?

A moving magnet, which carries with it a magnetic field, creates an electric field. That’s just the way our universe works. Changing magnetic fields create electric fields. Since an electric field exerts a force on any electrically charged particle, the charges in a wire are pushed around whenever a magnet moves past them.

Are there any objects that use compressed air to create electricity?

Moving air is used to create electricity: wind-powered generators. Compressed air is usually created with electrical power, so using it to generate electricity would be inefficient. But wind-powered generators are a common sight in some parts of the country. The wind blows on the turbine blades, doing work on them and providing the mechanical power needed to turn a generator. The generator converts this mechanical work into electrical energy.