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Electricity Harnessing energy for a better life Electric Charges Matter is made of atoms, Electrons can be moved from one atom to which are made of another, but protons electrons, protons, and cannot move. neutrons. Electrons have a negative When an atom has gained electrons, it is negatively charge, and protons have charged. a positive charge. When an atom has lost electrons, it is positively charged. Rule of Charge: Opposite charges attract, and like charges repel. Charge and Force Electrons can be rubbed Like charges repel each off of one object and onto other, and unlike charges another. The objects get attract each other. The area around a charge a static charge. where you can feel force is When neutral objects are called the electric field. rubbed together and The electric field is charges are rearranged, strongest when you are the objects get unlike closest to the charge and charges, and they stick gets weaker as you get together. farther away from the charge. Static Electricity A neutral object builds up Charging by friction a static charge by gaining happens when objects or losing electrons. rub together and An electroscope can be electrons are transferred. used to tell detect a static Charging by conduction charge. happens when a charged Static electricity can be object touches another caused in 3ways: friction, object and electrons are conduction, or induction. transferred. Charging by induction happens when a charged object held close to another object causes charges to be rearranged. Conductors and Insulators Most metals are good Materials through which conductors because of their electrons cannot move electrons can move from easily are called atom to atom in a “sea of insulators. electrons.” Electrons are tightly Acids, salt water and tap bound to the atoms of water are also good good insulators and conductors of electricity. cannot move from atom Pure distilled water does to atom. not conduct electricity. Wood, ceramic, rubber, Materials through which glass, and many plastics electrons can move easily are good insulators. are good conductors. Charges can build up on the surface of good insulators, and stay there as a static charge. Lightning! When a highly charged cloud is over land, During a storm, water and another charged area on dust particles are rubbed the ground is produced together by winds. Static charges build up because of by induction. Charges are now separated! friction. Charged areas of the clouds Lightning is caused by the discharge touch other areas, and (equalization) of this charged particles are transferred within clouds by static electricity. conduction. Electric Current Electric current happens when Electrochemical cells electrons move, or flow and thermocouples through a wire or some other cause the voltage kind of conductor. that makes electrons flow. These devices For electricity to flow, you need a closed continuous path, are sources of free electrons. called a circuit. You also need a difference in There are two kinds of electrochemical charge from one end of the cells---wet cells (a wire to the other that pushes car battery) and dry the electrons through the cells (flashlight conductor. This is called batteries). voltage. Types of Current AC and DC current: When the electrons flow in only one direction through a conductor, this is called direct current, or DC. When electrons first go in one direction, then back, then forward again, this is called alternating current, or AC. Current from batteries is DC, and current from electric power plants is AC. DC electricity comes from here! AC electricity comes from here! Types of Circuits A circuit in which the A circuit in which the current must pass current can travel through all of the through more than resistors on only one one path is called a path is called a series parallel circuit. circuit. Ohm’s Law Three things can be measured when electrons flow through a circuit. 1) 2) 3) How many electrons flow through the circuit each second is called current. The letter I stands for current. Current is measured in amperes (A). The “push” behind electrons in a circuit is called voltage. The letter V stands for voltage. Voltage is measured in volts (V). The force opposing the flow of electrons through a circuit is called resistance. The letter R stands for resistance. Resistance is measured in ohms (Ω). Lights, radios, and other electric appliances cause resistance in a circuit. Ohm’s Law shows the relationship between these things and says: I= V/R V I R Electric Power and Safety Electric power and electric Be safe when using energy can be calculated electricity! using the following formulas: Never remove the P P = V I ground wire from a V I plug. Power = voltage times current Never use electric appliances near water, E E = P t because water is a P t conductor! Energy = power times time Never overload circuits or replace burned out fuses with pennies. This can cause a short circuit, which could start a fire.