Electricity

Electric Charges Matter is made of atoms, which in turn are made of electrons, protons, and neutrons. Electrons have a negative charge, and protons have a positive charge. Neutrons have no charge. Electrons can move from one atom to another, but protons cannot move . When an atom has gained electrons, it has more electrons than protons, and it is negatively charged. When an atom has lost electrons, it has more protons than electrons, and it is positively charged. Rule of Charge: Opposite charges attract, like charges repel.

Charge and Force Electrons can be rubbed off of one object and onto another. The objects then get a static charge. When neutral objects are rubbed together and charges are rearranged, the objects get unlike charges, and they stick together. Like charges repel each other, and unlike charges attract each other. The area around a charge where you can feel force is called the electric field. The electric field is strongest when you are closest to the charge. Charged balloon sticks to charged area of a wall.

Static Electricity A neutral object can build up a static charge by gaining or losing electrons. An electroscope can be used to tell detect a static charge. It cannot tell if the charge is positive or negative. Static electricity can be caused in 3ways: friction, conduction, or induction. Charging by friction happens when objects rub together and electrons are transferred. Charging by conduction happens when a charged object touches another object and electrons are transferred. Charging by induction happens when a charged object is held close to another object and that causes charges to be rearranged.

Conductors and Insulators Materials through which electrons can move easily are good conductors. Most metals are good conductors because of their metallic bonds and their “sea of electrons.” Acids, sea water , and tap water are also good conductors of electricity. Distilled water does not conduct electricity. Materials through which electrons cannot move easily are called insulators. Electrons are tightly bound to the atoms of good insulators and cannot move around. Wood, ceramic, rubber, glass, and many plastics are good insulators. Charges can build up on the surface of good insulators, and stays there as a static charge.

Lightning! During a storm, water and dust particles are rubbed together by winds. Charges build up in the clouds because of this friction. Charged areas touch other areas of the clouds, and some charges are transferred within clouds by conduction. When a highly charged cloud is over land, a charged area on the ground is produced by induction. Charges are now separated! Lightning is caused by the discharge (equalization) of these separate static electric charges. - charge - charge + charge + charge - charge - charge

Electric Current Electric current happens when electrons flow through a wire or another conductor. For electricity to flow, you need a closed continuous path, called a circuit. You also need a difference in charge from one end of the wire to the other that pushes the electrons. This is called potential difference or voltage. Electrochemical cells and thermocouples cause the voltage that makes electrons flow. There are two kinds of electrochemical cells---wet cells such as a car battery and dry cells like flashlight batteries.

Types of Current There are two types of electric current--AC and DC current. When the electrons flow in only one direction, this is called direct current., or DC. Current from batteries is always direct current. When electrons first go in one direction, then reverse, then back again, this is called alternating current, or AC. Current from generating plants that powers our homes and businesses is alternating current.

Ohm’s Law Ohm’s Law relates the push behind electric current to the number of electrons flowing and to the resistance to their flow. The rate of electrons flowing through a circuit is called current. The letter I stands for current. Current is measured in electrons per second or Amperes or amps (A). The “push” behind electrons in a circuit is called voltage. The letter V stands for voltage. The unit for voltage is Volts (V). The force opposing the flow of electrons through a circuit is called resistance. The letter R stands for resistance. The unit for resistance is the Ohm (Ω) Ohm’s Law says: I = V / R V I R

Types of Circuits A circuit in which the current must pass through all of the resistors on only one path is called a series circuit. A circuit in which the current can travel through more than one path is called a parallel circuit. #1 #2 #3

Electric Power and Safety Electric power and electric energy can be calculated using the following formulas: P = V I Power = (voltage)(current) E=Pt Energy = (power)(time) Be safe when using electricity! Never remove the ground wire from a plug. Never overload circuits or replace burned out fuses with pennies. This can cause a short circuit, which could start a fire. Never use electric appliances near water, because tap water is a conductor! Stay away from windows and electrical appliances during thunder storms. P V I E P t