An electric circuit is a path in which electrons from a voltage or current source flow. Electric current flows in a closed path called an electric circuit. 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". The load of an electrical circuit may be as simple as those that power electrical 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 very big converters.
Electronic circuits[change | change source]
Electronic circuits usually use low voltage 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.
Circuit and wiring diagrams[change | change source]
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 skilled draftsmen, and then printed. Diagrams may also be created digitally using specialised software.
Wiring and circuit diagrams use special symbols recognized by everyone who uses the drawings. The symbols on the drawings show how components like resistors, capacitors, inductors, 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.
Resistors and other circuit elements can be connected in series or in parallel. Resistance in series circuits is the sum of the resistances.
Circuit breakers[change | change source]
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 (GFI) devices[change | change source]
The standard return for electrical and electronic circuits is the earth ground. When an improperly designed 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 interrupt devices detect open circuits to earth ground in attached electrical or electronic devices. When an open circuit to earth ground is detected, the GFI device immediately opens the voltage source to the device. GFI devices are similar to circuit breakers, but are designed to protect humans rather than circuit component.
Schematics[change | change source]
A schematic is a diagram of an electrical circuit. A schematic doesn't look like a life like a circuit, but it does show the essential connections. Schematics use symbols to represent components in the circuit. We use conventions in a schematic, we use them to represent the way electricity flows. The common convention we use is from the positive to the negative terminal. The realistic way electricity is from the negative to the positive terminal.