Matter is everything. Everything is matter. You, your computer, your desk, your food, the air, the entire earth, it is all made out of matter. What is matter? Well, matter is atoms. Atoms are the tiny building blocks that make up everything in the universe. Since this isn't a chemistry class (Chemistry is the study of matter and atoms) we will not go in-depth when describing atoms. However, you will need some basic knowledge, so here it is.

Atoms are not really little building blocks. They don't look like the "Lego" you played with when you were a little kid. They aren't like tiny basketballs nor can we compare them to particles of dust. Atoms are nothing like anything we have in our world, and they are really quite interesting.

In the center of an atom, there is a tiny "core" called the nucleus. This core is heavy (in comparison to the rest of the atom, not in comparison to a 1984 chevy truck) and is responsible for most of the atoms weight. It is made up of 2 types of particles, which are grouped tightly together. They are neutrons and protons. Neutrons have no charge, they are just heavy inert particles. Protons have a "positive" charge. What does positive really mean? Well, in this case, it means that it attracts to a negative charge. It doesn't mean that the protons are "good" and the other particles are bad. (If you think that is the case, seek psychiatric help.)

Did we mention negative charge? Yes, there it is in the previous paragraph. Negative charge exists in another type of tiny particle, the electron. Electrons are also parts of atoms. Electrons orbit the nucleus at high speeds, at a relatively far distance. (Remember, far still means microscopically far!) Unlike the proton, the electron has almost no mass. However, the "negative" charge on one electron is exactly the same in magnitude when compared to the positive charge of a proton. Yet you must remember that the charges are opposites. Since they have the same magnitude of charge, one proton's force cancels out one electron's force. It just so happens that in a neutral atom, there are the same number of protons as there are electrons. Therefore, there is no net charge, and there is no net force.

You may have noticed that "electron" and "electricity" are sort of similar. Well, that is no accident. Electrons are the only parts of the atom which are not static. Electrons move. Atoms can lose electrons. Atoms can gain electrons. Electrons move. This is the basis of electricity- the movement of electrons.

There are two main types of electricity. The first type is "Static" Electricity. You may be familiar with this type of electricity. When you rub your feet on a carpet, and touch someone, you sometimes notice a spark. If you've ever been hit by lightening, you are probably TOO familiar with static electricity; lightning is static electricity too. Static electricity is usually the result of friction. You should have read about friction in our dynamics section. If you didn't, then the phlying physicists are mad at you. The force of friction between two objects sometimes causes electrons to "rub off" of one material, and adhere to another. What does this mean? Well, the object that lost the negatively charged electrons becomes positive. The object that gained the electrons is now too negative, and has a net negative charge. The two materials will now attract. Opposite charges attract. This is because the atoms "want" to equalize the charge. The atoms "don't like" having extra charge, and they will transfer the excess of electrons whenever possible. Notice that we use "want" and "don't like" in quotation marks. These particles aren't intelligent. Electrons don't want anything, and they can't be your friend, so don't even ask them.

The concept of static electricity should be coming clear. Excess electrons can accumulate on an object, and cause it to become negative. Electrons can be removed from an object, and cause it to become positive. That's it... well, almost.

Objects don't have to be charged by the physical transfer of electrons. Lets say you charged a rod negatively, by rubbing it on the carpet. Then lets say you had a device for detecting static charge. This device is called an electroscope, and you'll be able to see an illustration of one in a minute. Physicists need to be patient. If you bring the charged rod near to one end of the electroscope, all of the negative charges in that end of the electroscope will be repelled by the rod. Like charges repel. These like charges will move to the other end of the electroscope, charging the far end negatively and the near end positively. You have just charged two ends of the electroscope, and you didn't even touch it. This is called induction. You are inducing the electrons to move. If you were to actually touch the rod to the electroscope, you would be charging by conduction.

One last thing. Lets say you touch the negatively charged rod to the earth. Just stuck it into the ground. Pretty soon, there would be no charge on the rod. But the earth hasn't become negative. And the earth wasn't positive to start with, there were no unlike charges to attract each other. What happened to the negative charge? It flowed into the earth, in a process called grounding. Grounding is the neutralizing of a charge. The charge becomes so spread out by the earth, that it is effectively gone. Ground an object when you want to get rid of the charge.

Since you are an observant individual, we are sure that you noticed the words "repel" and "attract" and immediately thought of "push" and "pull." You may remember (you SHOULD remember) that a FORCE is a push or a pull. If there is attraction and repulsion between positively and negatively charged objects, there must be a force present. As physicists, we must calculate that force.

As this very page has stated, protons and electrons have the same magnitude of charge. How much is that? Not much. Charge is measured in a unit called the Coulomb (C). One electron has 1.6 E-19C of charge. That isn't much, but it is one of those numbers that you just need to know.

The Coulomb was named after a scientist whose name was Coulomb. What a coincidence. He was a pretty smart guy though, and he came up with the formula that we use to calculate the force of static electricity. It is called Coulomb's Law, and looks like this:


F=K q1 q2 / d^2

or, "Force equals a constant times the charge of the first particle times the charge of the second particle all divided by the distance squared." That shouldn't be too much for a bright person like you to learn. If you want to find the force between 2 electrons, 1 meter apart, you just plug in the values. K is equal to 9E9 Nm^2/C^2.

F=(9E9) * (1.6E-19) * (1.6E-19) / 1^2
F= 2.30E-28 N (Not a lot of force!)

A force is not only present between charged particles. A force also exists between a charged particle and a neutral particle. Any charge attracts a neutral body.

Speaking of forces, we should go into more detail about the forces around charged particles. A charged particle creates what physicists call an electric field. Fields are very important when you learn more and more physics. Whatever enters an electric field experiences a force caused by that field. Fields aren't just imaginary- we use them in all kinds of physics applications. Fields have a direction- a field has the direction that a positive charge takes inside it. So if you put a proton in a field, and it moves to the left, that is the direction of the field. Field strength can me easily calculated. The formula is:


E = F / q

Where E is the field intensity, F is the force on the charged particle, and q is the amount of charge on that particle. The formula is often written as F=Eq, and is used to caluulate the force on a particle in a field.

	Click here to be taken to a home page with an interactive electricity applet. It is fairly compley, but you should be able to see how fields and charges interact.
	Click here to be taken to a home page with a great java experience. You can place charges and then the program will draw lines which let you see where the field would be.

Remember how we said that charges tend to balance out? That is, if a positive, conducting material is in contact with a neutral, conducting material there will be a transfer of electrons, and thus a transfer of charge. Scientists can't always refer to the object with more charge as "that object with more charge" and the object with less charge as "that object with less charge." Physicists apply the term "high potential" to objects with great positive charge, and the term "low potential" to objects with great negative charge. Therefore, negative charges flow from low to high, and positive charges from high to low. If two objects have really different charges, they have a high potential difference. The higher the potential difference, the more readily charge will flow between them. I bet you'll be surprised when we tell you that physicists have an equation to calculate a potential difference. Oops. We told you. We ruined the surprise.


V = Ed

V is the potential difference. The unit of potential difference is the volt. One volt is one joule per Coulomb (J/C). Volts are measured with a device called a Voltmeter. E is the field intensity, and d is the distance.



Pop quiz: What's the charge on one electron? Answer: (It's written 3 or 4 paragraphs up!) 1.6E-19c

How, you may ask, did people first figure that number out? Did they take an icepick and chip all of the charges off of an electron? No. A scientist named Millikan wanted to get the exact charge, so he built a device to measure it. He used an atomizer (fine spray) to charge a tiny particle, then it fell through a hole and between two plates of high potential difference. He adjusted the potential difference of the plates to suspend the drop in mid air. The force of the field on the particles was the same as the force of gravity (mg)! He had to use X-rays to isolate single electrons from the drop.

F=Eq
F=mg
Eq=mg
q=mg/E

Millikan knew what E, m and g were. All he had to do was plug the numbers into his equation, and viola! Instant charge measurement. It was a phenomenal achievement, you can be thankful he did it and you don't have to. But you should at least know about it. No charge less than Millikan's number has ever been found, even on such advanced particles as quarks (we won't get into that here, you can wait until you're in university. ) This in itself proves his measurement to be correct, because the electron is the smallest charged particle.