Circuits Electricity travels in closed loops, or circuits. It must have a complete path before the electrons can move. If a circuit is open, the electrons cannot flow. When we flip on a light switch, we close a circuit. The electricity flows from the electric wire through the light and back into the wire. When we flip the switch off, we open the circuit. No electricity flows to the light.
Electrical Circuits Electrical Circuits FLOW OF ELECTRONS
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WIRES
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LOAD ENERGY SOURCE
When we turn on the TV, electricity flows through wires inside the set, producing pictures and sound. Sometimes electricity runs motors— in washers or mixers. Electricity does a lot of work for us. We use it many times each day. In the United States, we use electricity to light our homes, schools, and businesses. We use it to warm and cool our homes and help us clean them. Electricity runs our TVs, DVD players, video games, and computers. It cooks our food and washes the dishes. It mows our lawns and blows the leaves away. It can even run our cars.
Conductors and Insulators
CLOSED SWITCH
A closed circuit is a complete path allowing electricity to flow from the energy source to the load. FLOW OF ELECTRONS
Have you ever wondered why some materials are used more often in electrical devices than others? It is because some objects conduct electricity better. A conductor is a material in which the outer electrons are not held as tightly as they are in other materials. When electrons are able to flow easily from atom to atom in an object, we call the object a conductor. If the electrons are not able to easily move around, we call the substance an insulator. Most metals make good conductors, with silver and copper being the best. Most non-metals are poor conductors. Substances such as plastic and rubber are good insulators and are used to coat wires used in electrical circuits.
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WIRES
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LOAD ENERGY SOURCE
OPEN SWITCH
Measuring Electricity Electricity makes our lives easier, but it can seem like a mysterious force. Measuring electricity can be confusing because we cannot see it. We are familiar with terms such as watt, volt, and amp, but we often do not have a clear understanding of these terms. We buy a 60-watt light bulb, a tool that needs 120 volts, or a vacuum cleaner that uses 8.8 amps, and we don’t think about what those units mean. Using the flow of water as an analogy can make electricity easier to understand. The flow of electrons in a circuit is similar to water flowing through a hose. If you could look into a hose at a given point, you would see a certain amount of water passing that point each second. The amount of water depends on how much pressure is being applied—how hard the water is being pushed. It also depends on the diameter of the hose. The harder the pressure and the larger the diameter of the hose, the more water passes each second. The flow of electrons through a wire depends on the electrical pressure pushing the electrons and on the cross-sectional area of the wire.
An open circuit has a break in the path. There is no flow of electricity because the electrons cannot complete the circuit.
Good Conductor
Good Insulator
� Voltage
The pressure that pushes electrons in a circuit is called voltage. Using the water analogy, if a tank of water were suspended one meter above the ground with a one-centimeter pipe coming out of the bottom, the water pressure would be similar to the force of a shower. If the same water tank were suspended 10 meters above the ground, the force of the water would be much greater, possibly enough to hurt you. © 2017 The NEED Project
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