ELECTRICITY AND MAGNETISM
Moving Electrons and Charges
Electricity is related to charges, and both electrons and protons carry a charge. The amount of the charge is the same for each particle, but opposite in sign. Electrons carry a negative charge while protons carry positive charge. The objects around us contain billions and billions of atoms, and each atom contains many protons and electrons. The protons are located in the center of the atom, concentrated in a small area called the nucleus. The electrons are in motion outside of the nucleus in orbitals. The protons are basically trapped inside the nucleus and can’t escape the nucleus. As a result, it is moving electrons that are primarily responsible for electricity.
There aren’t a lot of places that you can see electricity. The most commonly- observed form of electricity is probably lightning. Lightning is a big spark that occurs when lots of electrons move from one place to another very quickly. There are three basic forms of lightning, cloud to cloud, cloud to surface, and surface to cloud. All are created when there is an unequal distribution of electrons. You can also see smaller arcs of electrons at home when you scuff your feet and then touch something like a metal doorknob (static electricity).
Electricity Around You
It’s easy to see the uses of electricity around you. In fact, there are charges around your computer, your house, and your city. Electricity is constantly flowing through all of the wires in your town. There is also electricity in your flash light. That kind of electricity created by batteries is called direct current. The other major type is found in the outlets of your house. That household form of electricity is called alternating current.
The best real-life example of direct current is a battery. Batteries have positive (+) and negative (-) terminals. If you take a wire and connect the positive and negative terminals on a battery, the electrons in the wires will begin to flow to produce a current. You can prove that the current is flowing if you connect a small light to the circuit. The light will begin to glow as the electrons pass through the filaments.
DC power is used all over the world. You will probably use direct current power whenever you carry something around that uses electricity. Everything that uses batteries runs on DC power. Other countries use more portable power supplies because they might not have electric wiring in their houses.
That electric wiring in your house is AC power and it is completely different than DC. There are machines that can convert DC to AC power. Those machines might be used to take a DC battery in a boat and convert the power to AC so that a refrigerator can use it.
Cheaper and Stronger
Why do we use AC power all over the world? It’s cheaper and easier to make devices for AC power. It is less expensive because you can increase and decrease the current for AC power very easily. The power switches for AC power are also less expensive to manufacture. Probably the biggest advantage of AC is that you can use high voltages with small currents to reduce losses when you transmit power. Remember that lost energy increases the more collisions you have, and reducing current decreases the amount of collisions (and reduces heating in the wires). You can send power with DC, but the DC power transmission loses a lot of energy. You would have to put much more effort into sending DC power over the same distance.
Alternating Around You
BIG NOTE: NEVER touch the outlets in your house. You will get electrocuted. There is more to electricity than voltage. It’s the current that will kill you.
The easiest place to see AC power in action is in your house. All of the appliances and lights in your house probably run off of AC power. There are also power converters that change DC power into AC power when you need electricity and there are no plugs around (like camping).
Conductors and Conductivity
There are many materials that allow charges to move easily. They are called conductors. Conductors have the quality of conductivity. I guess that’s not a lot of help for you. The reality is that you just need to understand the difference between those two words. The conductor is the object that allows charge to flow. Conductivity is a quality related to the conductor. A material that is a good conductor gives very little resistance to the flow of charge. This flow of charge is called an electric current. A good conductor has high conductivity. Metals are traditional conducting materials. You see them around the house all of the time. It’s a metal wire or one of the metal prongs in an electric plug. There are a lot of free electrons in metallic conductors. Free electrons are electrons that are not being held in atoms, and so, can move easily. Some of the best metallic conductors are copper (Cu), silver (Ag), and gold (Au).
Force of Charges
Scientists discovered that opposite charges attract, and like charges repel. So positive-positive and negative-negative would repel, while positive-negative would attract. Physicists use the term electric force to describe these attractions and repulsions. The electric forces are much stronger when negative charges are closer to positive charges. The further apart two charges are, the weaker the electric force. Also, the greater the charges, the greater the electric force will be.
An electric field describes the funky area near any electrically-charged object. Scientists don’t use the word “funky”, but it works. It could also be called an electrostatic field. There are two kinds of charges, and some combinations attract while others repel. So, if the central charge was positive, and you put another positive charge near it, that second charge would be repelled outward. If the central charge is negative, a positive charge placed nearby would be attracted toward the center charge. Electric fields can also be created by magnetic fields. Magnetism and electricity are always connected.
A magnet is an object or a device that gives off an external magnetic field. Basically, it applies a force over a distance on other magnets, electrical currents, beams of charge, circuits, or magnetic materials. Magnetism can even be caused by electrical currents.
While you might think of metal magnets such as the ones you use in class, there are many different types of magnetic materials. Iron (Fe) is an easy material to use. Other elements such as neodymium (Nd) and samarium (Sm) are also used in magnets. Neodymium magnets are some of the strongest on Earth. Most of the magnets you see around you are man-made. Since they weren’t originally magnetic, they lose their magnetic characteristics over time. Dropping them, for example, weakens their magnetism; as does heating them, or hammering on them, etc.
Electromagnets have a ferromagnetic material (usually iron or steel) located inside of the coils of wire.
They depend on currents of electricity to give them magnetic characteristics. Not only can they be turned on and off, but they can also be made much stronger than ordinary magnets.
http://www.youtube.com/watch?v=E8AZBR8Zz04 Series and Parallel Circuits (Video)
http://www.bbc.co.uk/schools/podsmission/electricity/annie_game.swf Game about building a circuit
http://www.upscale.utoronto.ca/GeneralInterest/Harrison/Flash/EM/Buzzer/Buzzer.html How to build a simple buzzer
http://www.msnucleus.org/membership/slideshows/historyelectricity.swf Electricity and magnetism