Series and parallel circuits

Electrical current is a flow of electric charge. Circuits are circular paths along which electricity travels. Electricity moves from its source, through the wires and any elements connected to the circuit, and back to its origin. Circuits may either be linked in series or run in parallel.

Overview

Electric current is the flow of free electrons, which carry electrical energy with them. In a circuit, electrons move through conductive material, which is usually a metal wire such as copper. This wire and the current may pass through electrical elements or components. The circuit may also have a switch that creates a gap in the path, which stops the electricity. An off switch creates this open circuit.

Electrons in a circuit may flow in one direction—called direct current (DC)—or may flow in both directions—called alternating current (AC). Batteries produce direct current, while the power grids that supply homes and businesses with electricity use alternating current. This discussion will focus primarily on DC circuits.

Many circuits provide power to devices such as light bulbs and appliances. Basic circuits may include resistors and batteries, while more complicated circuits may include capacitors and inductors. Active elements, such as batteries and generators, generate energy. Passive elements, such as resistors, cannot generate energy and often use energy.

When a circuit has two or more components, they must be connected. They are connected by electrical junctions or wires called nodes. Current in a circuit flows from a high voltage to a lower voltage, for example, from the positive terminal of a battery to the negative terminal of a battery.

Series and Parallel Circuits

In a series circuit, the electric current flows in one continuous stream through the components, which share a common node, and returns to the power source. In a parallel circuit, components share two common nodes.

Imagine a group of people running along the edge of a football field in one direction and returning to the starting point; this is like a series circuit. Imagine half of the runners break away from the group. At the 50-yard line, they cut across the field and return to the starting point. The rest of the people continue running the full circumference of the field. The shortcut is like the path of a parallel circuit. Runners could take many shortcuts across the field—at the 10-, 30-, 70-, and 90-yard lines, for example—illustrating the way multiple parallel circuits may be added to an electric circuit.

Series and parallel configurations may work together. A component may be in series with a parallel combination, for example. As long as the current finds a path back to its source, many variations of series and parallel circuits may be created. The amount of current flowing through all components in a series current is the same because the flow of electrons has only one path to take. The current is not split.

A series circuit is useful in warning that a component in the circuit has failed. For example, older styles of strings of Christmas lights were series circuits. When one bulb failed, the entire string of bulbs would fail to light. Newer light strings are constructed as parallel circuits, allowing all the good bulbs to light up even when one bulb fails. The lights in homes and other buildings are also constructed as parallel circuits, so one broken element will not affect the rest of the elements on the circuits. Using parallel circuits means a person can turn a light on or off independent from the rest of the lights on the circuit.

Components in Circuits

Electrical components may be combined in series or parallel circuits to fill specific needs. Resistors provide electrical resistance, which limits the electron current through a circuit. This helps control the voltage. Resistors may also divide voltages. They may be combined in parallel to increase their resistance and manipulate the voltage of a circuit.

Capacitors are useful for storing energy locally, suppressing voltage spikes, and filtering complex signals. Capacitors, which can store energy, are composed of an insulating material called a dielectric sandwiched between two metal plates. Because the electric current cannot bridge the gap made by the dielectric, one plate holds the free electrons and becomes negatively charged. This negative charge pushes away the like charge, making the other plate positively charged. The larger the plates are, the greater their capacity to hold electrons. The charges of the plates attract each other, but the dielectric plate blocks the attraction. This clash creates an electric field, which can be held by the capacitor. Spacing the plates farther apart, however, decreases the strength of the electric field. Capacitors are helpful in regulating power supply, among other uses.

Inductors are tightly wound coils of wire. When a current passes through an inductor coil, it creates a magnetic field. The inductor can briefly store some energy. The coil conducts current and builds a magnetic field. When the current is interrupted, the magnetic field briefly keeps the current flowing before the field collapses.

Bibliography

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