Circuits 6-1

Electrical Flow Electric current is electric charge that flows. However charge doesn’t flow continuously through a material unless the material forms a closed path, or loop. A Circuit is a closed path through which a continuous charge can flow.

Parts of a Circuits Voltage Source Conductor Switch Electrical Device

Example

Voltage Sources In a circuit this provides electrical potential for the charge to flow. Batteries are often the voltage sources in a circuit.

Conductor A circuit must be a closed path in order for charge to flow. In order to do so there must be a conductor, such as a wire, that forms a connection from the voltage sources to the electrical device and back

Switch A switch is a part of a circuit designed to break the closed path of charge. When a switch is open, it produces a gap in the circuit so that the charge cannot flow.

Electrical Device An electrical device is any part of the circuit that changes electrical energy into another form of energy. A resistor is an electrical device that slows the flow of charge in a circuit. When the charge is slowed some energy is converted to light or heat. A light bulb is an example of a resistor.

Circuit Diagrams Symbols are used to represent the parts of a circuit. The circuit diagrams below show the circuit of the previous picture in both open and closed positions.

Open and Closed Circuits Current in a circuit is similar to water running through a hose. However, there is one difference between water and electrical flow. If you cut the hose, the water continues to flow. However if you cut a wire, the charge stops flowing. Batteries have connections at both ends so that charge can flow a closed path to and from the battery.

Open and Closed Circuits cont Switches work by opening and closing the circuit. A switch that is on closes the circuit and allows the charges to flow. A switch that is off opens the circuit and stops the current.

Short Circuits A short circuit is an unintended path connecting one part of a circuit with another. The current in a short circuit flows a closed path, but the path is not the one it was intended to follow. Pg 174

Grounding In many electrical plugs one prong is dedicated to being a ground. If there is a short circuit the charge might flow dangerously to the outside the shell of the appliance. However a ground wire, the current will flow safely into the ground, along either a buried rod or a cold water pipe.

Fuses Are a safety device designed to open a circuit when there is too much current running in it. Usually consists of a thin strip of metal that is inserted into the circuit. If a fuse is blown the fuse must be replaced to close the circuit.

Other safety devices Modern homes do not use fuses. Instead they use other devices known as circuit breakers. These do not have to be replaced each time they open the circuit. When a short circuit or overload occurs a switch is flipped causing the circuit to open.

Other safety devices cont. Another safety device is a Ground-fault Circuit Interrupter outlet (GFCI). These are required in places where exposure to water is common. A tiny circuit inside the GFCI outlet monitors the current going out and coming in. If current flows through an unintended path the circuit stops the current.

Assignment Read Section 6-1 Pg 177 problems 1-6

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