Kissimmee Homeschooling
Electromagnitism
What is a Magnet?
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.
Different Types of Magnets
There are many different types of magnets. Permanent magnets never lose their magnetism. There are materials in the world that are calledferromagnetic. Those materials are able to create and hold a specific alignment of their atoms. Since many atoms have amagnetic moment (tiny magnetic field), all of the moments can add up to create a magnet. Scientists use the wordhysteresis to describe the way the atoms stay aligned.
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.
There are also air-core magnets. Air-core magnets are created by current flowing through a wire. That current produces the magnetic field. You create an air-core magnet by wrapping miles of wire around in a doughnut shape (toroid). When you send current through the wire, a magnetic field is created inside of the doughnut. Scientists sometimes use air-core magnets to study fusion reactions.
Electromagnets are different because they have a ferromagnetic material (usually iron or steel) located inside of the coils of wire. The core isn't air, it is something that aids in producing magnetic effects, so electromagnets are typically stronger than a comparable air-core magnet. Air-core and electromagnets can be turned on and off. They both 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. You might see an electromagnet at work in a junkyard lifting old cars off the ground.
AC and DC Differences
Magnets Made Easy
A Direct Current
There are two main types of current in our world. One is direct current (DC) which is a constant stream of charges in one direction. The other is alternating current (AC) that is a stream of charges that reverses direction. Let's look at DC power which was refined by Thomas Edison in the 1800s.
Thomas Edison
Moving in One Direction
The current in DC circuits is moving in a constant direction. The amount of current can change, but it will always flow from one point to another. Before we move on, we need to explain that physicists, as well as electricians, refer to something called conventional current.
Do you remember that we talked about physicists agreeing to always use positive charges to determine how electric field lines would be drawn? Following through on that agreement, they also agreed to explain charge flow in terms of positive charges rather than electrons. So although electrons would flow from negative to positive, by convention (agreement), physicists refer to conventional current as a flow from high potential/voltage (positive) to low potential/voltage (negative). Reminding you that potential is like electrical height, this means that conventional current flows "downhill", which makes sense.
Electrons move from areas where there are excess of negative charges to areas where there are a deficiency (or positive charge). Electrons move from "-" to "+", but conventional current is considered to move in the other direction. When you set up a circuit, conventional current is considered to move from the "+" to the "-" side.
The idea about using positive charges in forming explanations comes fromBenjamin Franklin. In Franklin's day, we didn't know about protons and electrons. Franklin believed that something moved through electrical wires, and he called these things "charge". He assumed there was only one kind of charge, and he logically assumed that charge would flow from a spot that had an excess (extra), to a spot that had a deficiency (too few). He called the spot with an excess "positive" and the spot with a deficiency "negative". So, for Franklin, charge flowed from positive to negative. We simply honor his achievements by continuing with this idea.
Battery Basics
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.
An Alternating Current
There are two main types of current in our world. One is direct current (DC), which is a constant stream of electrons in one direction. The other is alternating current, which is a stream of charges that reverses direction. Scientists such as Charles Proteus Steinmetz andNikola Tesla made great advances when AC power was just a science experiment.
Flowing Back and Forth
Charges (electrons) must always be flowing to have a current. However, the flow of charges does not always have to be in one direction. In alternating current, the charges move in one direction for a very short time, and then they reverse direction. This happens over and over again.
Scientists describe the cycle of switching directions as the frequency. Frequency is measured in Hertz (Hz). Currents thatcycle more often during a specific amount of time are said to have a higher frequency. AC power cycles 60 times per second in the US.
Since the web is a global resource, we should also mention that there are different alternating current frequencies across the world. While we all use alternating current, the switching happens different amounts during a specific time period. Most countries use AC frequencies at either 50 hertz or 60 hertz.
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).
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 chargewhile 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 sparks of electricity in science labs that contain Van de Graff generators, and can see even smaller arcs of electrons at home when you scuff your feet and then touch something like a metal doorknob (static electricity).
Electrons, Protons and Neutrons
Battery Basics
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
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.
Separating Charges
Atoms start out with the same number of negative charges (electrons), and positive charges (protons). Under certain conditions, electrons can be removed from, or added to atoms. Removing electrons would leave the atom with more positives than negatives, and we call this a positive ion (An ion is a charged atom). Conversely, adding electrons to an atom would result in a negative ion. If you do this enough times, you can make an object positive or negative.
Friction is one of the ways to separate charge. Have you ever had a science lab where you rub fur on glass rods, or try to make static cling? When you do that rubbing, you are actually rubbing electrons off one object and onto another. When you scuff your feet on the rug, especially in the winter, you can often charge yourself. Clothes tumbling in the dryer often cling together and crackle when you separate them. Lightning is produced, in part, because of air blowing over land. You can also use batteries to separate charge.
Static Charges
Electrons can move more easily in some objects than in others. If you put a charge on things like glass, plastic, rubber, and wood, that charge stays where you put it. We say the charges are static, and we call this static electricity. Materials like glass and plastic are called insulators, ornonconductors. Static electricity can happen on a dry winter day when you walk across a carpet. You are actually building up loads of electrons on your skin. Charges don't "want" to stay separated, however. There is always a tendency for charges to return to their original locations, and all that is needed is a pathway for charges (electrons) to use. When you touch a metal doorknob, for example, electrons can jump and give you a shock. Static charges build up on clouds until they can hold no more. At that point, lightning can occur. The study of electricity where the charges are not moving is called electrostatics.
Conductors and Conductivity
There are many materials that allow charges to move easily. They are calledconductors. 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 allowscharge to flow. Conductivity is a quality related to the conductor. A material that is a good conductor gives very littleresistance to the flow of charge. This flow of charge is called an electriccurrent. A good conductor has high conductivity.
Different Types of Conductors
(1) 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).
(2) There are some conductors that are not metals. Carbon is the best example.
(3) You've probably seen ionic conductors in a lab or in an experiment. When you think about ionic conductors, think about solutions and molten conductors. A solution such as saltwater has a lot of free ions floating around. Those ions (charged atoms) can flow easily, and ionic solutions are very good conductors. One of the reasons you need to get out of the water if there is lightning around, is that water normally contains dissolved ions, and if lightning hits the liquid (solution), it might conduct electricity long distances and electrocute you.
(4) Semi-conductors are the conductors that make your computer possible. If it weren't for semi-conductors, most electronic doodads couldn't be made. Semiconductors have free electrons, but not as many as conductors, and they are not as easy to get moving. Semiconductors have low conductivities. Examples are elements like silicon (Si) and germanium (Ge).
Let Them Move
So what happens if you have separated charges and you connect them with conducting material? Providing a path for charges to move, and making that path out of materials that allow easy movement, results in a flow of charge (electrons) called a current. The electrons will flow from a location that is negative to one that is positive. This can happen quickly and then stop, as with a spark. Or, in the case of a battery connected to a conducting loop (called a circuit. ), it continues to happen until the battery runs out of energy. If the current goes in one direction all the time, it is called DC, or direct current. In your home, however, the same charges move back and forth, so this is called AC, or alternating current.
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.
Field Basics
Scientists understood why forces acted the way they did when objects touched. The idea that confused them was forces that acted at a distance without touching. Think of examples such as gravitational force, electric force, and magnetic force. To help them explain what was happening, they used the idea of "field". They imagined that there was an area around the object, and anything that entered would feel a force. We say, for example, that the Moon has agravitational field around it, and if you get close to the Moon, it will pull you down to its surface.
Electric Fields
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. Any other charge that enters that area will feel a force, and the original object will also feel that force (Newton's Third Law). It's kind of like a spider sitting at the center of a web.
A normal field is a vector, and is represented by arrows. The Earth's (or any planet's) gravitational field would be drawn as arrows pointing toward the ground. A field vector shows the direction of the effect on an object entering the field. Gravity acts downward.
For an electric field, things are a little more complicated, since there are two kinds of charges, and some combinations attract while others repel. In order to be in agreement with each other, physicists decided that they would always use positive charges to determine the direction of the effect of a field. So, if the central charge was positive, and you put another positive charge near it, that second charge would be repelled outward. So the field vectors for a central positive charge point outward. If the central charge is negative, a positive charge placed nearby would be attracted toward the center charge, so the field vectors for a central negative charge point inward.
Since fields are directly related to the forces they exert, their strength decreases with distance, and increases with the size of the charge producing the field. When you put charges near one another, their fields interact and change shape. This results in changes in the PE of the objects, and generates forces of repulsion or attraction.
Magnetic Field Basics
Magnetic fields are different from electric fields. Although both types of fields are interconnected, they do different things. The idea of magnetic field lines and magnetic fields was first examined by Michael Faraday and later by James Clerk Maxwell. Both of these English scientists made great discoveries in the field of electromagnetism.
Magnetic fields are areas where an object exhibits a magnetic influence. The fields affect neighboring objects along things called magnetic field lines. A magnetic object can attract or push away another magnetic object. You also need to remember that magnetic forces are NOT related to gravity. The amount of gravity is based on an object's mass, while magnetic strength is based on the material that the object is made of.
If you place an object in a magnetic field, it will be affected, and the effect will happen along field lines. Many classroom experiments watch small pieces of iron(Fe) line up around magnets along the field lines. Magnetic poles are the points where the magnetic field lines begin and end. Field lines converge or come together at the poles. You have probably heard of the poles of the Earth. Those poles are places where our planets field lines come together. We call those poles north and south because that's where they're located on Earth. All magnetic objects have field lines and poles. It can be as small as an atom or as large as a star.
Attracted and Repulsed
You know about charged particles. There are positive and negative charges. You also know that positive charges are attracted to negative charges. A French scientist named Andre-Marie Ampere studied the relationship between electricity and magnetism. He discovered that magnetic fields are produced by moving charges (current). And moving charges are affected by magnets. Stationary charges, on the other hand, do not produce magnetic fields, and are not affected by magnets. Two wires, with current flowing, when placed next to each other, may attract or repel like two magnets. It all has to do with moving charges.
Earth's Magnetic Field
Magnets are simple examples of natural magnetic fields. But guess what? The Earth has a huge magnetic field. Because the core of our planet is filled with molten iron (Fe), there is a large field that protects the Earth from space radiation and particles such as the solar wind. When you look at tiny magnets, they are working in a similar way. The magnet has a field around it.
As noted earlier, current in wires produces a magnetic effect. You can increase the strength of that magnetic field by increasing the current through the wire. We can use this principle to make artificial, adjustable magnets called electromagnets, by making coils of wire, and then passing current through the coils.
Electric fields can also be created by magnetic fields. Magnetism and electricity are always connected. We'll talk about magnetic fields in the next section.