# Charges

Picture this: your alarm clock shrilly rings; your flailing arm finally connects with the snooze button. You roll out of bed and mumble, "Thank goodness it's Friday." You shuffle towards the kitchen, your pink bunny slippers slowly dragging you across the carpet. You reach for the doorknob and....SNAP....a flash of miniature lightning sparks from the doorknob to your finger. Welcome to the world of charges.

You've probably experienced the above scenario hundreds of times in your life. By rubbing your slippers on the carpet, you have given your body an electric charge. Charge is one of the properties of all matter. It has a natural tendency to be transferred between unlike materials. By dragging your feet, you increased this natural transfer.

When scientists first began to study this phenomena, they discovered that there were two kinds of charge. Benjamin Franklin (1706-1790) named these two kinds positive and negative. One of the earliest observations made of charged objects was that unlike charges attract, while like charges repel. A positive and a negative will pull each other together. Two positive or two negative charges will push each other away.

Charge has another important property. Electric charge is always conserved. For example, say you have two neutral, or uncharged, objects, and you rub them together. Let's say object #1 gets a positive charge. Object #2 must have transferred some of its positive charge to #1. Object #2 has become negatively charged.

A famous physicist named Robert Millikan discovered a third property of charge. Charge can only be found in integer multiples of a fundamental "piece" of charge. He called this piece of charge e. An electron has a charge of -e, while a proton has an opposite, but equal in magnitude charge, +e. There is no way to get a charge of +2.71e, because there are no parts of e, although there could be +2e, there could not be +.71e.
Note: Quarks are an exception to this rule, and have charges of +2/3 or -1/3. Some of the particles physicists used to consider fundamental are actually composed of quarks. This is an advanced topic, and will not be covered here in much depth.

We classify materials into four different types, based on their ability to conduct charge. The four types are: insulators, semiconductors, conductors, and superconductors.

• Insulators are materials like rubber, glass, and wood. These materials do not conduct charge well at all.
• Semiconductors are materials like silicon and germanium. They conduct a moderately small amount of electricity. They are used in a wide variety of electrical devices because their electrical properties can be changed dramatically by adding small amounts of other atoms.
• Conductors are materials like copper, aluminum, and gold. They conduct most of the electricity that is passed through them.
• Superconductors are materials that conduct ALL of the charge that goes through them. They have many useful applications. Unfortunately, to show the property of superconductivity, a material must be kept very, very, cold.
The unit of charge is named the coulomb (abbrev. C) in honor of Charles Coulomb, a French pioneer in electricity and magnetism. +e is equal to approx. 1.60219e-19 C. Charles Coulomb also established the relationship between the magnitude of the electric force between two charges, the magnitude of those charges, and the distance between them. The law is named for him, Coulomb's Law.
 Force = k (a special constant) * first charge * second charge / the square of the distance between them k = 8.9875*109 N*M2/C2
It is important to note that the Coulomb force is a field force. It acts even though there is no physical contact between the two particles.

You may be thinking to yourself, "This formula is great! If I have two particles. What happens if I have three or more charges?" The answer to your question is The principle of superposition. This law states that if you have three charges, 1, 2, and 3, the charge exerted on charge 1 by the combination of charges 2 and 3 is the vector sum of the force of charge 2 on 1 and the force of 3 on 1. This holds for particle groups of 3, 4, 5, etc.