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## Introduction to Electricity

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##### 1. Atoms and Electric Charges
Atoms are made up of protons, neutrons and electrons. Both protons and electrons have an electric charge. Protons are positively charged and electrons are negatively charged. Neutrons are not charged particles.
##### 2. Interaction of Charged Particles
The interaction of electric charges is called electricity. If particles have opposite electric charges, they attract each other. If particles have similar charges, they repel each other. These interactions explain why an atom is held together. The positively charged protons in the nucleus exert a strong attraction for the negatively charged electrons that surround the nucleus.
##### 3. Electric Fields
The attraction or repulsion that exists between charged particles is known as electric force. The area around a charged particle, where an electric force is exerted, is called an electric field. For a negatively charged particle, electric force lines are drawn pointing inward toward the particle. For a positively charged particle, the lines are drawn outward. The lines on the diagram are close together right next to the particle, where the field is the strongest.
##### 4. Multiple Charged Particles
When two charged particles come close together, their electric fields are combined. The top diagram represents the electric fields of particles that are attracted. The bottom diagram shows the electric fields of particles that are repelled.
##### 5. The Movement of Electric Charges
Objects do not normally have a positive or negative charge. However, within the atoms of some materials, the electrons are able to leave and move to other atoms. When an object gains or loses electrons, the object can become charged. Some materials, like copper and aluminum, are called conductors because their electrons can easily move. Other materials, like plastic, are known as insulators, because their electrons will not easily move.
##### 6. How Objects Become Charged
There are several ways that an object can become charged, and electrons can be transferred. Friction is the transfer of electrons between two uncharged objects that are rubbing against each other. Conduction is the transfer of charges when a charged object is in direct contact with another object. Induction is the movement of electrons within an object in response to an electric field of a charged object nearby. The electrons movement creates a charge in a certain area of the object.
##### 7. Static Electricity
Static electricity occurs when electric charges build up on an object, but the electrons do not flow. Static electricity is what causes lightning. An excess of positive charges builds up on the ground while a large number of negative charges builds up in the clouds. At a certain point, the difference between the negatively charged cloud and the positively charged ground is so great that the static electricity turns into an electrical current. The bolt of lightning is actually a discharge of electrons traveling at the speed of light toward the positive charges. In the 1700s, Benjamin Franklin studied lightning and electricity. He invented the lightning rod to protect buildings during storms.
##### 8. Electroscope
An electroscope is an instrument used to detect charged particles. It has a long metal rod with a knob on top and two metal leaves attached to the bottom. The leaves hang straight down if the electroscope has no charge. If a charged object touches the knob and electrons are transferred, the metal leaves become charged. Because the leaves are the same charge, they repel each other and spread apart. The leaves will move in the presence of a negative or positive charge. An electroscope can tell us if an object is charged, but it cannot tell us if the charge is negative or positive.