In this blog post, we’ll explain the roles and characteristics of resistors (R), inductors (L), and capacitors (C)—the basic components of electrical circuits—in an easy-to-understand way.
Basic Components of the Digital and Analog Worlds
As digital broadcasting and digital communications have become commonplace, many devices have been replaced by complex semiconductor-based electronic circuits. However, the fundamental components that have underpinned the analog world remain at the core of electrical engineering. The three classic components primarily used in analog circuits—resistors (R), inductors (L), and capacitors (C)—each create relationships between voltage and current in distinct ways and continue to play a central role in countless electronic devices today.
These three components are indispensable in the history of electrical engineering and serve as the most fundamental elements for understanding the operation of analog circuits. By appropriately combining these three components, a wide variety of functions can be implemented, and this is the fundamental reason why devices such as televisions and radios could be created using electricity.
Voltage and Current: Explained Using the Analogy of Water
When we say “electricity flows,” we are referring to the movement of electrons within a wire. The force that drives the electrons is voltage, and the magnitude of that movement is current. Voltage and current are often compared to the height of water and the flow of water; just as water flows from a higher place to a lower place, current tends to flow when voltage is applied.
While the relationship between height and flow in water is relatively simple, the relationship between voltage and current is much more complex. A higher voltage does not always result in a greater current, and the specific relationship between voltage and current is determined by components such as resistors, inductors, and capacitors. Therefore, the simple analogy of water alone cannot fully explain all the characteristics of electrical phenomena.
Principles and Applications of Resistors (R), Inductors (L), and Capacitors (C)
A resistor is a component that restricts the flow of current and is made of materials such as alloys or carbon. When a voltage is applied across the two ends of a resistor, current flows; however, the electrons passing through the resistor collide with the atoms that make up the resistor, hindering their flow. Because of this, a simple relationship holds in which the current flowing through a resistor is proportional to the voltage, and the power can be released as heat or light, which is utilized in the principles of electric heaters and light bulbs.
An inductor is typically a device made by winding a long wire into a coil, and it stores current in the form of a magnetic field. If the flowing current remains constant, the generated magnetic field also remains constant; however, if the current changes, the magnetic field changes as well. Since the natural world has a tendency to resist changes in state, an inductor generates its own voltage in a direction that opposes changes in current, thereby momentarily suppressing changes in current. Thanks to this property, inductors are used to prevent sudden current fluctuations, thereby eliminating noise or protecting equipment from sparks, and they also play a key role in devices that utilize magnetic fields, such as transformers.
A capacitor consists of two metal plates separated by an insulator; when a voltage is applied, electrons accumulate on one plate, making that side the positive terminal and the opposite side the negative terminal. Since a capacitor responds to changes in voltage rather than current itself to allow current to flow, it has characteristics that are the exact opposite of an inductor. In other words, an inductor generates voltage due to changes in current, while a capacitor allows current to flow due to changes in voltage. For this reason, capacitors are used to block effects caused by slow changes in voltage or to temporarily store electrical energy.
By appropriately combining these three basic components, many dynamic relationships in the real world can be modeled. For example, certain physical phenomena can be explained using a simple proportional relationship like that of a resistor, while phenomena related to rate of change or variation can be understood through the characteristics of inductors or capacitors. However, to commercialize actual products, all practical constraints—such as power consumption, cost, size, speed, and the feasibility of mass production—must be taken into account.
Due to these practical constraints, as well as the high speed, small size, and low defect rates offered by semiconductors, digital devices have rapidly dominated the market. Nevertheless, it is noteworthy that for hundreds of years, countless useful machines have been built using only these three components—resistors, inductors, and capacitors—and that they continue to play an important role today when used in conjunction with analog circuits.
