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The point where those electrons enter an electrical circuit is called the "source" of electrons. The point where the electrons leave an electrical circuit is called the "return" or "earth ground". The exit point is called the "return" because electrons always end up at the source when they complete the path of an electrical circuit.
The part of an electrical circuit that is between the electrons' starting point and the point where they return to the source is called an electrical circuit's "load". A load of an electrical circuit may be as simple as those that power home appliances like refrigerators, televisions, or lamps or more complicated, such as the load on the output of a hydroelectric power generating station.
Circuits use two forms of electrical power: alternating current (AC) and direct current (DC). AC often powers large appliances and motors and is generated by power stations. DC powers battery operated vehicles and other machines and electronics. Converters can change AC to DC and vice versa. High-voltage direct current transmission uses big converters.
Electronic circuits usually use direct current sources. The load of an electronic circuit may be as simple as a few resistors, capacitors, and a lamp, all connected together to create the flash in a camera. Or an electronic circuit can be complicated, connecting thousands of resistors, capacitors, and transistors. It may be an integrated circuit such as the microprocessor in a computer.
Resistors and other circuit elements can be connected in series or in parallel. Resistance in series circuits is the sum of the resistance.
Circuit and wiring diagram
A circuit or wiring diagram is a visual display of an electrical circuit. Electrical and electronic circuits can be complicated. Making a drawing of the connections to all the component parts in the circuit's load makes it easier to understand how circuit components are connected. Drawings for electronic circuits are called "circuit diagrams". Drawings for electrical circuits are called "wiring diagrams". Like other diagrams, these diagrams are usually drawn by draftsmen, and then printed. Diagrams may also be created digitally using specialised software.
A schematic is a diagram of an electrical circuit. Schematics are graphical representations of the essential connections in a circuit, but they are not lifelike depictions of a circuit. Schematics use symbols to represent components in the circuit. Conventions are used in a schematic to represent the way electricity flows. The common convention we use is from the positive to the negative terminal. The realistic way electricity flows is from the negative to the positive terminal.
Circuit diagrams use special symbols. The symbols on the drawings show how components like resistors, capacitors, insulators, motors, outlet boxes, lights, switches, and other electrical and electronic components are connected together. The diagrams are a big help when workers try to find out why a circuit does not work correctly.
The current flowing in an electrical or electronic circuit can suddenly increase when a component part fails. This can cause serious damage to other components in the circuit, or create a fire hazard. To protect against this, a fuse or a device called a "circuit breaker" can be wired into a circuit. The circuit breaker will open, or "break", the circuit when the current in that circuit becomes too high, or the fuse will "blow". This gives protection.
Ground-fault-interrupt (G.F.I.) devices
The standard return for electrical and electronic circuits is the earth ground. When an electrical or electronic device fails, it may open the return circuit to the earth ground. The user of the device could become a part of the device's electrical circuit by providing a return path for the electrons through the user's body instead of the circuit's earth ground. When our body becomes part of an electrical circuit, the user can be seriously shocked, or even killed by electrocution.
To prevent the danger of electrical shock and the possibility of electrocution, ground fault interrupts devices detect open circuits to earth ground in attached electrical or electronic devices. When an open circuit to earth ground is detected, the G.F.I. device immediately opens the voltage source to the device. G.F.I. devices are similar to circuit breakers but are designed to protect humans rather than circuit components.
Short circuits are circuits that get back to the power source unused or with the same power as put out. Using these usually blow a fuse but sometimes they don't. Doing this with a battery can cause electrical fires.