Electric Circuits: Components, Types, and Related Concepts


By Robert Hazen, Ph.D., George Mason University
Image of a bulb and battery in a simple open and close circuit.
A diagram of a simple open and closed electric circuit. (Image: BijanStock/Shutterstock)

Electric circuits are important concepts that have practical applications in our daily lives. It is a very simple concept that incorporates three different components—a source of electrical energy, a device, and a closed loop of conducting material.

Source of Electrical Energy

 The first component in an electric circuit is the source of electrical energy that allows electrons to move. This source could be a battery, a solar cell, or a hydroelectric plant—a place where there’s a positive terminal and a negative terminal and from where charge could flow from one to the other. This push of electric charge is called voltage whose potential is measured in volts.

Device in the Electric Circuit

The second component is the device. It responds to the current passing through it. Today, a device is something that can be plugged into a wall socket and used with electricity. The loop is generally closed using a piece of conducting material. It is usually a wire but there are other kinds of materials that can close the loop too. For example, there are various strips of metal inside the television that have been deposited onto a plastic surface that may be the conducting material or even in some cases, the chassis of a device that becomes part of the closed circuit.

Resistance of the Electric Circuit

The third component is the resistance; every circuit has some resistance to the flow of electrons. Electrons collide with other electrons and atoms that make up the wire and they, thus, convert some of their energy to heat. It is simply not possible to transfer energy from one form to another without losing some of that energy as heat.

Learn more about electromagnetism.

Flashlight as an Electric Circuit

The flashlight is a simple device that incorporates all three of these components. The two batteries in the flashlight are the source.

The light bulb at the end of the flashlight is the device into which the current flows. Current flows through a very tiny filament which heats up to a very high temperature because of the electrical resistance. As a result, the filament glows brightly.

The circuit is finally completed by a strip of metal that goes down the side barrel of the flashlight. There is also a coil of wire at one end of the flashlight and at the other end there are the contact points for the battery as well as the other strip of wire that together complete the circuit.

 Illustration of an electric circuit comprising a battery, a bulb, a switch and a wire.
A simple electric circuit has a source, device, resistance, and a switch. (Image: BlueRingMedia/Shutterstock)

Switch, Fuse, and Circuit Breakers

Flashlights and most other electrical appliances also have a switch. A switch is merely a device that helps to break the continuous loop of the conducting material.

When the switch is open, there is no flow of current but when the switch is closed, there is a flow. Basically, all circuits work like this. Even in the circuit plugged into the wall of your room, there’s a continuous loop of wire that extends from your home all the way to the power plant.

A fuse or a circuit breaker is used to prevent major fires due to overloads. A fuse is designed to burn up if the current gets too high.

Learn more about the first law of thermodynamics.

Types of Electric Circuits

There are two types of circuits found in homes and other common devices; namely series circuits and parallel circuits.

Series Circuits— Series circuits consists of several devices, each of them linked up one after another after another in just a single large loop. Though,different devices have different voltages across them, the same current flows through every device in the series circuit.

If any one of the devices in a series circuit is broken, the whole circuit fails. For instance, if there are three light bulbs connected in a series, in just one loop of wire connected to a battery. If one light bulb is unscrewed, the whole circuit fails.

Parallel Circuits —In parallel circuits, different devices are arranged so that a single source supplies voltage to separate loops of wire. The voltage in every device across the circuit is exactly the same, but in general different devices are going to see different currents. In this case, each device is going to work even if the other ones fail.

For instance, if two light bulbs are linked up in parallel and one is unscrewed, the other one will work. Modern Christmas tree lights are done in parallel circuits so that even if a single light burns out, the whole strand doesn’t have to be thrown out.

This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.

Systematizing Relationships between Electric Circuits – Kirchhoff’s Laws

The systematized behavior of circuits is of immense importance in electrical engineering and is explained by Kirchhoff’s Laws. The first law states, “The energy produced by the source equals the energy consumed in the circuit, including the heat that is lost as a result of resistance.” 

The second law states,The current flowing into any junction equals the sum of the currents flowing out of that junction.” This means that current is electrons flowing through the wires and the number of electrons flowing into a junction equals the number of electrons flowing out of that junction. 

Learn more about entropy.

Are Different Forms of Electrical Energy Fundamentally the Same?

A painting of Michael Faraday.
Michael Faraday was an English scientist who contributed to the study of electromagnetism and electrochemistry. (Image: Thomas Phillips/Public domain)

Michael Faraday made careful systematic surveys of all these different kinds of electricity. He was able to demonstrate that all of these different forms of electricity produced exactly the same kind of phenomenon and resulted from the movement of electrons.

Faraday concluded that all forms of energy produced sparks, can flow through wires, and can be made to do work. His research also showed for the first time that animal electricity of an electric eel, the electricity coming from a battery, and the electricity of lightning were all one and the same phenomenon.

Electric Current and Power

The flow or movement of electrons through the electrical circuit is called the electrical current. Current is measured in amperes. One ampere corresponds to about 6 billion electrons passing a point in that circuit every second.

Another important term associated with electricity is power. Power is defined as work divided by time. In an electrical circuit power equals current voltage, measured in watts. The higher the wattage, the faster the energy consumed by that object, be it a light bulb, an amplifier, or any electrical device.

Learn more about magnetism and static electricity.

Common Questions about Contributions of Alessandro Volta and Invention of the Battery

Q: How does a light bulb in the flashlight glow?

When current flows through a very tiny filament, it heats up to a very high temperature because of the electrical resistance. This causes the filament to burn brightly and, thus, the light bulb in the flashlight glows.

Q: How are fuse and circuit breakers helpful?

Fuse and circuit breakers are designed to prevent electrical equipments from being damaged due to overload. While fuses need to be replaced after an overload, circuit breakers need to be just reset.

Q: What is an electric current?

The flow of electrons through an electrical circuit is called the electrical current and is measured in amperes.

Q: Why did Christmas tree light chain of olden days become useless even if one bulb burned out?

The Christmas tree lights of olden times were a series type of circuit where if one bulb did not work, the whole circuit would fail. However, modern Christmas tree lights follow the principle of parallel circuits

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