Resistors are devices that are used in a variety of circuits to make the currents and voltages that you desire. The resistor is the simplest circuit element. In a resistor, the voltage is proportional to the current, with the constant of proportionality R, known as the resistance. Resistance has units of ohms, denoted by Ω, named for the German electrical scientist Georg Ohm. This simple element has lots of benefits and drawbacks for the systems.
There are two types of elements found in electric circuits: passive elements and active elements. An active element is capable of generating energy while a passive element is not. Examples of passive elements are resistors, capacitors, and inductors. The resistor is the simplest passive element. The resistor is always positive. Thus, a resistor always absorbs power from the circuit. This confirms the idea that a resistor is a passive element, incapable of generating energy.
Resistors have many advantages and disadvantages for the systems. Let’s check them.
Advantages of resistors
The following list can help you to understand the benefits of resistors.
Simple working principle and construction
Conventional forms of resistor obey a straight-line law (Ohm’s Law) when voltage is plotted against current and this allows us to use resistors as a means of converting current into a corresponding voltage drop, and vice versa. Therefore, resistors provide us with a means of controlling the currents and voltages present in electronic circuits. They can also act as loads to simulate the presence of a circuit during testing. All resistors have a simple construction and they apply to all circuits easily.
What is Ohm’s Law?
Ohm’s Law states that, at a constant temperature, the electric current flowing in a conducting material is directly proportional to the applied voltage and inversely proportional to the resistance. Ohm’s Law is the relationship between power, voltage, current, and resistance. These are the very basic electrical units we work with.
The size of a resistor is compact. It does not need so much space in the electrical circuit. Besides, it is very easy to carry them from one place to another place.
Resistors are cost-friendly. You can buy thousands of them at affordable prices. You can easily replace them without considering costs.
Resistors do not require maintenance. Their body is strong. To construct circuits, resistors are usually made from metallic alloys and carbon compounds that require almost zero maintenance.
Wide application areas
Resistors are often used to model devices that convert electrical energy into heat or other forms of energy. Such devices include conducting wire, light bulbs, electric heaters, stoves, ovens, and loudspeakers.
Another application where resistors are used to control current flow is in the analog dc meters—the ammeter, voltmeter, and ohmmeter, which measure current, voltage, and resistance, respectively.
The resistor has various types such as wire-round, carbon-composition, film-type, surface-mount, fusible, and thermistors. Each has a different feature in the circuit.
A resistor is either fixed or variable. Most resistors are of the fixed type, meaning their resistance remains constant. Variable resistors have adjustable resistance. Although resistors are used in circuit designs, today most circuit components including resistors are either surface mounted or integrated. It should be pointed out that not all resistors obey Ohm’s law. A resistor that obeys Ohm’s law is known as a linear resistor.
The electrical lifetime of resistors is long. You can use them for years without any replacement.
Easy to identify
Carbon and metal oxide resistors are small, so these types of resistors are normally marked with color codes that indicate their value and tolerance. Colors represent numerical values. You can easily identify the R-value and tolerance from the color codes marked on the resistor.
Sometimes used in temperature sensing
With conventional resistors, we would normally require resistance to remain the same over a wide range of temperatures. On the other hand, there are applications in which we could use the effect of varying resistance to detect a temperature change. Components that allow us to do this are known as thermistors. The resistance of a thermistor changes markedly with temperature and these components are widely used in temperature sensing and temperature compensating applications.
Can be light-dependent
Light-dependent resistors (LDR) use a semiconductor material (i.e. a material that is neither a conductor nor an insulator) whose electrical characteristics vary according to the amount of incident light.
Can be variable
Variable resistors are available in several forms including those which use carbon tracks and those which use a wire wound resistance element. In either case, a moving slider makes contact with the resistance element. Most variable resistors have three (rather than two) terminals and as such are more correctly known as potentiometers.
The resistance of a voltage-dependent resistor falls very rapidly when the voltage across it exceeds a nominal value in either direction. In normal operation, the current flowing in a voltage-depended resistor is negligible, however, when the resistance falls, the current will become appreciable and a significant amount of energy will be absorbed.
Disadvantages of resistors
Following are the drawbacks of the different types of resistors.
Since resistors are positive-valued, resistors always dissipate power. But where does a resistor’s power go? By conservation of power, the dissipated power must be absorbed somewhere. The answer is not directly predicted by circuit theory but by physics. Current flowing through a resistor makes it hot; its power is dissipated by heat.
Resistor power ratings are related to operating temperatures and resistors should be derated at high temperatures. Where reliability is important, resistors should be operated well below their nominal maximum power dissipation.
Due to the very nature of their construction, resistors can short out internally. They may, however, become short-circuited by another component in the circuit.
Extra information: A short circuit is a resistor with zero resistance. An open circuit is a resistor with infinite resistance.
Dust and corrosion
Some controls (especially volume and tone controls) may become noisy or scratchy-sounding, indicating a dirty or worn-out resistance element.
The ideal resistor never deviates from its rated value, is unaffected by temperature, can handle any electrical load, and does not change its specifications throughout its life. However, real-world physics always gets in the way of this ideal.
The value marked on the body of a resistor is not its exact resistance. For example, the 1 kΩ resistor you can hold in your hand is not exactly an ideal 1 kΩ resistor. Some minor variation in resistance value is inevitable due to production tolerance. A resistor marked 100 Ω and produced within a tolerance of ±10% will have a value that falls within the range 90 Ω to 110 Ω.
The resistance value can change under thermal, electrical, or mechanical influence. Stability classes indicate the maximum permissible change. Stability is tested by procedures defined in standards.
Due to inhomogeneities in the resistor material or substrate and/or poor transitions between terminations and resistor material, even linear resistors are not completely linear.