Electrical Circuits

For electricity to flow, it needs an electrical circuit, which is a path along which electrons from a current source flow, from the point of excess negative charge to the point of the lesser negative charge.

The point where electrons enter an electrical circuit is called the source of electrons. The point where the electrons leave an electrical circuit is called the return. 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 source and the return is called the load. An electrical load is anything that uses electricity to do work or to perform a job (ranging from a simple light bulb to heavy machinery).

Electricity must have a complete path along the circuit, for it to flow. A switch in an electrical circuit closes or opens it. Closing the circuit is the equivalent of turning on the flow of electricity, and opening it is the equivalent of turning off the flow of electricity.

A short circuit is an electrical circuit that allows a current to travel along a path with zero or very low resistance. It results in an excessive current flowing through the circuit. It is not advisable since a very high current may generate a correspondingly high amount of heat causing the medium through which the current is flowing to overheat and potentially catch fire. Therefore, any circuit must have a reasonable load to limit the flowing current before it is connected to a source of electricity.

Series and Parallel Circuits

Components of an electrical or electronic circuit can be connected in series or parallel. In a series circuit, components are connected with a single conductive path, so the same current flows through all of the components but voltage is dropped (lost) across each resistance or load. The sum of the voltages consumed by each resistance or load is equal to the source voltage.

In a parallel circuit, components are connected across multiple paths making the current split up across each path, keeping the voltage across each component the same.

Consider a very simple circuit consisting of two light bulbs and a 12-volt battery. If a wire connects the positive connector of the battery to one connector of the bulb and the second connector connected to the next bulb, which is connected back to the negative connector of the battery in one continuous loop then these bulbs are said to be in series. If a wire runs from the positive connector of the battery to one connector of the bulb and then back to the negative connector of the battery with one separate wire for each bulb, the bulbs are said to be in parallel.

In a series circuit, every connected device should function to complete the circuit. If one bulb burns out in a series circuit, the entire circuit is broken. In a parallel circuit, each bulb has its own circuit, so even if one of the bulbs burns out, the other one will still function. If a switch is required to turn the bulbs on or off, in a series circuit, only one switch will turn all the bulbs on or off together, while in a parallel circuit, each bulb can have its own switch and can be turned on or off independent of the others. Generally, household wiring is in parallel since each light, appliance, or socket usually needs to be switched on and off separately. Electronic circuits are a combination of series and parallel connections.