Every time you rode in a car or bus, you got somewhere because chemical energy was transferred to heat energy, which was then transferred to mechanical energy. Every time you ate something cooked or baked, from soup to dessert, you ate food that was made with heat energy. Every time you pushed a switch to turn on a light or a TV set, you used electrical energy.
            Your home has many electrical devices, yet the energy comes from a powerhouse that may be hundreds of miles away. Electrical energy is the most convenient form of manmade energy because the source doesn’t have to be close to the user.

Electrical Energy & Electrons

            Electrical energy is related to electrons, and electrons are parts of atoms. All atoms have a small inner part called a nucleus. The nucleus is made of protons and neutrons (with the only exception being ordinary hydrogen, which has no neutrons). All atoms have an outer part, consisting of electrons. In every atom, the number of electrons is always the same as the number of protons. The electrons whirl around the nucleus very rapidly—about a hundred million billion times a second! This is the motion of every electron in every atom.
            Electrons can be made to move in another way, from one atom to the next and the next. This motion, this flow of electrons, is called an electron current, or electric current, or electricity. Like anything that moves, electrons have energy when they are in motion. This energy of moving electrons is called electrical energy. Electrons repel each other. They push away from each other. In this way, we can get a moving current of electrons, an electric current.

Static Electricity

            When electrons are forced to flow through a gas, they can make it glow. Air is a gas. In dry air, as you comb your hair, you scrape away electrons from your hair onto the comb. The comb becomes charged with electrons. As you keep combing, you pile up a greater and greater charge of electrons. This charge, which is staying still, is called static electricity. Static means “staying still.” But electrons repel each other. as you increased the quantity of electrons, you also increased the force of repulsion among them. Finally the repulsion was so great that the electrons at the end of the comb nearest your head were forced off. They leaped through the air back to your hair. We say they discharged. This flow of electrons is current electricity. As the electric current flowed, it caused the air to glow (you can see this when the room is dark). Electrical energy was transferred to light energy. There was an input of mechanical energy. The mechanical energy produced a charge of static electricity. When the charge was great enough, it was discharged and became an electric current. The output of electrical energy was then transferred to light energy in a gas—the air.
            Other gases can be made to glow in the same way. Neon signs contain gases that light up when an electric current flows through them. So does a fluorescent tube.

Electricity in the Sky

            With lightning and thunder, huge charges of static electricity are built up by the swirling and rubbing of tiny droplets of water in the air and in clouds. Then, the static electricity in the sky discharges suddenly. It flows off in a giant leap. As the huge stream of electrons zips through the air, you see a flash—lightning…and you hear a crackly sound—thunder.
            Benjamin Franklin discovered that lightning comes from an electric current.

Steady Currents of Electricity

            A charge of electricity can discharge and become current electricity. But such a current is not useful for ordinary purposes because it comes in a burst, all at once. We need an even, steady flow to run our electric lights and machines. We need a way of pushing electrons steadily.
            Magnets can move electrons steadily. The electrons in atoms are tiny magnets. They can be moved in a steady stream by the steady push of a magnet.
            Michael Faraday discovered in 1831 that electrons can be moved by the force of a magnet. Faraday had an instrument for testing feeble electric currents. It is called a galvanometer.
            If the output of useful energy is much lower than the input energy, scientists say it has a low efficiency.

Generators

            A high-efficiency method. Most electric currents are produced by magnets. But magnets are not pushed back and forth. Instead the magnets are whirled around and around in a machine called a generator.
            The electric current for your community comes from generators in a powerhouse. These generators’ magnets are a special kind called electromagnets. These huge generators must produce a very large output of electrical energy. To do so, they must receive a very large input of mechanical energy.
            One source of mechanical energy is falling water. The falling water spins the blades of a water turbine. The turbine is joined to the shaft which turns the electromagnet of a generator. This method of transferring the mechanical energy of water to electrical energy is called a hydroelectric system. Hydro means “water.”

Electricity from Fuels

            There are places that have no water power for turning generators. They use the chemical energy in fuels such as coal or oil. When the fuel is burned, the chemical energy is transferred to heat energy. The heat energy turns an engine, and the engine turns a generator. This is called a fuel-electric system. In it, there are several energy transfers: from chemical to heat to mechanical to electrical.

Electricity from Nuclear Fuels

            In modern powerhouses, nuclear materials are used as a source of heat energy. The heat energy is transferred to mechanical energy by a steam turbine, just as in a fuel-electric system. The steam turbine turns a generator to produce an output of electrical energy. So the chief difference between nuclear-electric systems and fuel-electric systems is in the input energy. One pound of nuclear material gives more heat energy than two million pounds of coal.

Electricity from Chemical Energy

            We use chemicals to transfer chemical energy directly to electrical energy. Certain chemicals when packed together in a container will produce electricity. The whole thing is called a cell. A group of these cells attached together make up a battery.
            Inside a cell, the molecules of these chemicals separate into their atoms. These atoms combine with other atoms and form new molecules. Electrons are left over. The electrons pile up. When you connect the cell to a bulb, the electrons flow in a current. The electrons continue to crowd over to one part of the cell, out through the bulb, and back into another part of the cell. But as they release electrons the chemicals change. Bit by bit the cell loses its power to send out electricity. When all its power is gone, we say the cell is dead.
            A storage battery can be recharged. When an electric current is sent into it, the chemicals in the battery are changed back to their original condition. Once again, they can send out a flow of electrons.

Electricity from Light Energy

            There are certain materials whose electrons are pushed and crowded when light shines on them. As long as they receive light energy, they can keep sending out electricity.
            Perhaps you have seen a light meter used to measure the light for taking pictures. When light shines on it, electricity flows. Light energy is transferred to electrical energy.
            The electricity flows into a little galvanometer that measures the strength of the electric current. The needle on the dial of the light meter shows how bright the light is.

Solar Batteries

            A solar battery transfers light energy to electrical energy.

Measuring Electrical Energy

            The number of electrons flowing is measured in units called amperes. A one-ampere current has a flow of about 6 billion billion electrons per second. When you plug in an ordinary electric heater, it takes a current of about 10 amperes. 60 billion billion electrons flow through the heater in one second.
            The strength or force of these electrons is measured in units called volts. The electrons that come out of a dry cell have a force of 1 ½ volts. The electrons in your house current have a voltage of about 120. if you want to know the total power of an electric current, you need to know both the quantity of electrons (amperes) and the strength of each electron (volts). We measure this power in units called watts. We figure the watts by multiplying the amperes by the volts.

Electric Currents

            You need to have a complete circuit for an electric current. One wire allows electrons to flow from one part of the dry cell to the bulb. The other wire allows the electrons to flow from the bulb back to another part of the dry cell. The electrons can flow when there is a complete circuit from the dry cell, through the bulb, and back again.
            You need a complete circuit to operate an electric toaster, radio, or any other electrical device. You must have two wires—one comes from the source of the current, the other goes back to the source.
            Inside the cord of your toaster or electric iron there are two bundles of wire. The plug has two prongs. Each prong is connected to a bundle of wires. An outlet has two slots. Each slot is connected to a wire that leads to the powerhouse. When the two prongs are put into the two slots, we have a complete circuit through the two wires from the source of the current (the powerhouse) and back again.

How a Switch Works

            In a complete circuit the current keeps flowing. This could be a nuisance if the flow is through a bell that keeps ringing or a light that remains lit whether we want it or not. We must have a way to stop the current. A switch can do the job.
            Switches come in many shapes and sizes, but they all do the same job. They all have a metal part that can be moved to make a complete circuit, or to break it.

Switches for Special Jobs

            Most switches are operated by hand. But some switches work by changes in temperature. Such a switch is called a thermostat. Most thermostat switches have a metal strip called a compound bar. It is made of a strip of brass fastened to a strip of iron. When heated, brass expands more than iron. When cooled, brass contracts more. This causes the compound bar to bend one way when heated, the other way when cooled. So a change in heat energy is transferred to mechanical energy, the bending of the compound bar.

Feedback

            A thermostat is an example of feedback control. This method of control is used in factories, spacecraft, and thousands of other places. It is used for controlling many other things besides temperature. The feedback may be the weight of cornflakes in a box. Machines that are worked by feedback systems, without people to control them, are called automated machines. A water-level switch controls a pump that fills a water tank.

Good and Poor Conductors

            Because copper conducts electricity so well, it is called a good conductor of electricity.  The current that comes from a powerhouse can give a shock strong enough to kill a person. The wires that carry such a strong current have to be safely covered with insulation. Many different materials can be used for insulation. Some wires are insulated with rubber, and others with cotton. Whatever materials are chosen, you may be sure of one thing about them: They are all very poor conductors of electricity.
            When you touch an insulated wire, the current cannot flow into you because it cannot get through the insulation. The current is kept safely in place, in the wire.

Danger in a Short Circuit

            When the insulation is worn away, the wires may touch each other. the current has an easy roadway from one copper wire to the other, at the place where they touch. The current cannot flow as easily through the very thin wire inside a bulb. So most of the current flows across the easy path and very little flows through the bulb. This easy path is called a short circuit. The current will cause the wires to become very hot. A short circuit can be the cause of a dangerous fire. The wires in your house are protected by special parts called fuses or circuit breaker boxes.

Electromagnets and Permanent Magnets

            An electromagnet is a coil of wire around a metal bar. When electric energy flows through the wire, the bar becomes a magnet. Electromagnets are more useful than ordinary magnets because the magnetism can be made very strong. Electromagnets are more useful than ordinary magnets because the magnetism can be turned on and off. This is useful in many things—electric doorbells, telephones, electric motors, and others.
            A flow of electrons produces the effect of magnetism. A magnetic field is a space in which a magnetic force is experienced. The field exists only as long as current is flowing—that is, electrons are moving in the same direction—in the wire. When the electric current in the wire is made to stop flowing, the magnetic field ceases to exist.
            The magnetism of a permanent magnet also is generated by the electricity of moving electrons. In the atom, the electrons not only revolve about the nucleus but also rotate on their own axes. In a great many materials, the rotations of the electrons are in directions that cancel each other. in certain other elements, such as nickel and iron, the spins of some of the electrons aid each other to produce the effect of moving electricity. This moving electricity generates a magnetic force.
            Each atom in a piece of iron or nickel is, for the above reason, a tiny magnet. We could think of a small bar magnet as being the magnetic model of, for example, the iron atom. But iron does not normally exert a magnetic force, because the magnetic fields of the atoms cancel each other.
            Suppose that an iron paper clip is brought near a permanent magnet. The strong magnetic field of the permanent magnet will rearrange the iron atoms. More of the atoms in the clip will magnetically point in the same direction. Their magnetic fields will aid each other. the clip, magnetized, now exerts a magnetic force. It is attracted to the permanent magnet.
            When heat energy is added to matter, its atoms move much more rapidly. Because of this, the atoms will be so jarred that they will all point in different directions. Their magnetic fields will cancel each other. the heated iron will not show a magnetic effect.
            Some permanent magnets are made of very hard steel. The atoms in steel are strongly held in position. Permanent magnets stay magnetized for a long time. All their atoms remain pointed in the same direction. They can be demagnetized—lose their magnetism—by being dropped. Sudden jars or great heat will rearrange the atoms.
            Iron like that in paper clips is a soft metal. Its atoms are not strongly held in position. Because of atom vibrations, its atoms become magnetically mixed up even at low temperatures. Soft iron that has been magnetized will not hold its magnetism for very long.
            Magnetism is a different property of matter from electricity. It is a property of electricity in motion.