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Resistor definition

What is a resistor?

The Resistor is an electrical component that is used to create resistance in the flow of electricity. In nearly every electronic network and circuit, they are found. The measurement of resistance is in ohms (O). The term "ohm" refers to the resistance that is created when a current of 1 amp (A) is passed through the Resistor, with a single Volt (V) drop between its ends. It is proportional to the voltage that is across the terminals. This ratio is represented in Ohm's Law:


Resistors are utilized for various reasons. They can be used to limit the electric current, voltage division and heating as well as match and loading circuits, control gain, and set constants for time. They are available for sale with resistances in an area of over Nine orders. They can be utilized as brakes that use electricity to eliminate the energy generated by trains, or they can be larger than square millimetres in electronic devices.

Resistor definition

Resistor Definition and Symbol

The term "resistor" refers to a non-electrical component whose primary purpose is to restrict the flow of electricity.

The internationally recognized IEC symbol is rectangular in design with leads at both ends. In the USA, it is known as the ANSI standard and is widely used as a representation of an unassisted resistor in an elongated stripe.

Overview of Types and Materials

Resistor types can be classified by functional type as well as resistance materials. The following breakdown of kinds of resistors is possible:

  1. Fixed resistors
  2. Variable resistors, for example, like:
    • Potentiometer
    • Rheostat
    • Trimpot
  3. Resistors whose resistance value is determined by the physical quantity:
    • Thermistors: (NTC and PTC) The resistance is determined by temperature
    • Resistors for photos: The resistance is determined by light intensity
    • Varistors: The resistance is dependent on the voltage
    • Magneto resistors: resistance is determined by the magnetic field
    • Strain gauges: resistance is determined by the mechanical load

In each one of the kinds, there is a common symbol that exists. A different breakdown based on the manufacturing process and material could be created:

  • Carbon composition
  • Carbon film
  • Metal film
  • Metal oxide film
  • Wirewound
  • Foil

The selection of the technology used is based on the Resistor's use. In most cases, it's a compromise between precision, cost power, as well as other demands. For instance, carbon composition is a long-standing manufacturing technique that makes resistances with low precision. However, it is still utilized for certain applications in which high-energy pulses are generated. Carbon composition resistors come with bodies made of an amalgamation composed of carbon nanoparticles as well as the ceramic that is non-conductive.

Carbon film technology produces resistors that have a higher tolerance (less variation in resistance) over carbon composite resistors. They are made up of an inert rod that is covered with a thin layer of carbon film over it. This layer is treated using an arc cut to increase and regulate the resistance.

Metal oxide films and metals are popular in the present and offer superior properties to ensure stability and tolerance. They are also less affected by temperature variations. As with carbon film resistors, they are made of an insulating film that is wrapped around an elongated body. The metal oxide film is typically more robust.

Wirewound resistors are most likely the most ancient type that can be utilized for high precision and application with high power. They are made by winding a particular steel alloy wire, like nickel or chrome, over the non-conductive core. They are long-lasting, precise and have low resistance.

The disadvantage is that they are susceptible to parasitic reactions when they are operating at high frequencies.

For the highest standards of quality and stability, metal foil resistors are employed. They are created by glueing an alloy film on a ceramic substrate.

Resistor Characteristics

Based on the purpose, the electrical engineer will specify various properties for the Resistor. The primary goal is to restrict the flow of current. Therefore, the primary factor is resistance. The precision of manufacturing this value is reflected in the tolerance of the Resistor and is expressed in terms of per cent of the value of resistance (for instance, +-5%). Other parameters that impact the value of the resistance can also be specified, including long-term stabilities or even the coefficient of temperature. This coefficient of temperature, typically defined in high-precision applications, will be determined by the material used as Resistor and its mechanical structure.

In high-frequency circuits such as radio electronics, parasitic capacitance and inductance could cause undesirable consequences. Foil resistors typically have a lower parasitic reactance, and wire-wound resistors are one of the most problematic. In order to be able to use them in precise applications like audio amplifiers, electrical resistance has to remain as minimal as possible. It is usually stated as microvolts noise per volt of applied voltage for 1 MHz of bandwidth. For applications that require high power, the power rating is vital. This is the amount of working power that the component is able to handle without affecting its properties or causing damage. It is typically determined in free air at room temperature. Power ratings with higher power requirements require larger sizes and could even require heat sinks. Other factors can influence the design specifications. Examples include the maximum voltage or stability of the pulse. When surges of high voltage could occur, it is a crucial feature.

It is not always just the electrical properties that are vital. However, the designer also needs to take into consideration the durability of the machine in tough conditions. Military standards can provide guidance on how to determine the strength of the material or failure rate.

Resistor Standards

There are many standards that apply to resistors. They provide methods to measure and quantify the most important properties. Other standards exist for physical dimensions and resistance values. Perhaps the most well-known standard can be found in the code colour markings for axial-leaded resistors.

Colour code for Resistor

The Resistor has 5600-ohm resistance with a tolerance of 2 per cent in accordance with the marking code IEC 60062.

The value of resistance as well as tolerance is indicated by a series of coloured bands that are placed around the component body. This method of marking electronic components was first invented early in the 1920s. The printing technology was not yet fully developed, which caused numerical codes printed to be too complicated for small components. Today the colour code is employed for resistors axial up to 1 Watt. In this case, the two first bands are the most important digits of the resistance number; the third band determines the multiplier factor, and the fourth band provides the tolerance. Each colour is a unique number that is easily found on the chart of colour codes for resistors or using a colour code calculator.

Resistor Values (Preferred values)

The 1950s saw the growing production of resistors and triggered the necessity for standardizing the resistance values. The range of values for resistance can be standardized by using preferred values. The values that are preferred are defined in the E-series. In an E-series, every value is a specific percentage more than the previous. Different E-series are available for various tolerances.

SMD resistors

In the case of SMD (Surface Mount Device) resistors, a numeric code is utilized, as SMD resistors aren't big enough to be used for the colour code. SMD resistors are just like led resistors, typically available in the values that are most commonly used. The dimension of the element (length and width) is also standardized and is known as resistor packaging. The number "331" signifies that the Resistor has a value of 33Ω x 101 = 330 Ω.

Applications of Resistors

The whole range of use of resistors is quite vast. It can vary from precision components used in electronic circuits to measurement devices which are used to measure physical quantities. Since the usage is too high and varied, all the applications couldn't be mentioned, but some of the most well-known applications are discussed below-

1. Resistors in series and parallel

When designing electronic circuits, resistances can typically be placed in series or parallel. The circuit designer may use, for instance, multiple resistors using typical resistance values (E-series) to get the desired resistance. For connections in series, the current flowing through each Resistor is equal, while the equivalent resistance will be the sum of all the resistors. In parallel connections, every Resistor's voltage is equal. The reverse of the equivalent resistance is the total of the values that are inverse for each of the parallel resistors. For more intricate systems, Kirchhoff's circuit law could be employed.

2. Measure the electrical current (shunt resistor)

Electrical current can be determined by studying the voltage drop on an ultra-precision resistor that has an established resistance. It is connected in series to the circuit. The current is calculated using Ohm's law. This is known as an ammeter, also known as a shunt resistor. Most often, it is an extremely precise manganin resistor that has the lowest resistance.

3. Resistors for LEDs

LED lights require a particular voltage to function. If the current is too low, it won't light the LED, whereas a current that is too high could ruin the device. So, they're usually coupled with resistors to regulate the current. These are referred to as ballast resistors that control the current of the circuit.

4. Blower motor resistor

In automobiles, the air vent system is controlled by a fan that is controlled by the motor that blows it. A special resistor is employed to regulate the speed of the fan. It is referred to as the motor's Resistor. Different designs are used. One of the designs is a series of wire wound resistors in different sizes to match the fan's speed. Another design includes a fully integrated circuit printed on a circuit board.

5. Resistor usage in Circuit Functions

There are a variety of resistors that function according to the use. In this case, we are able to alter the resistance with the knob type of the feature. The change in resistance affects the flow of electricity within the circuit. Examples include the resistors used in controlling the motor's speed, the pitch of a musical tone or the volume of an amplifier, etc.

6. Resistors are used for Diving Voltage

The splitting of the voltage can be useful in situations where components have to perform their work at a lesser voltage than the input voltage. Connecting the resistors together can help reduce the voltage across each Resistor evenly, thus assisting the appliance to work smoothly in these conditions.

7. It is also employed for heating purposes

Due to the interactions of the ions within the material, certain obstructions generate resistance. This creates lots of heat when conducting current. We can see the use of resistors in a toaster, heater, microwave, electric stove, as well as other heating equipment. In a light bulb, the filament of the light bulb (made from tungsten) is white-hot because of the extremely high temperature that is a result of the resistance (slow electric flow) when electricity flows through it.

8. Uses of Resistor to function in particular timing and at a certain Frequency

Many circuits employ alternating resistors and capacitors to gain access to the source of timing. Devices like light flashers, LEDs that blink, electronic sirens, and numerous other circuits are dependent on this function. These are the devices employed in aircraft and high towers for collision avoidance tests. They operate on the principle of charging current up until a specific time and then releasing light. The Resistor determines the amount of current that needs to be passed at a certain moment. If the resistance of the circuit rises, then the time to discharge the circuit also rises. A capacitor is a storage device for an electric charge, just like buckets hold water. It takes a certain period of time to fully fill with the current. Its resistance is the measure of how quickly the capacitor fills up.

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