Resistor

A passive electrical component with two terminals that are used for either limiting or regulating the flow of electric current in electrical circuits. The main purpose of resistor is to reduce the current flow and to lower the voltage in any particular portion of the circuit. It is made of copper wires which is coiled around a ceramic rod and the outer part of the resistor is coated with an insulating paint.
SI Unit of Resistor is Ohm.

What is a resistor?

A resistor is a passive two-terminal electrical component that limits the current flowing in electrical or electronic circuits. Its property to resist the flow of current is called resistance, expressed in ohm (Ω), named after German physicist Georg Simon Ohm. Resistors are available in different sizes. Its size is directly proportional to its power rating. The power rating is the maximum amount of power that a resistor can dissipate without being damaged by excessive heat build-up. The larger the surface area covered by a resistor, the more power it can dissipate.

Types Of Resistors

Linear resistor
Non-linear resistor

Linear resistors

The resistors whose values change with change in applied temperature and voltage are known as linear resistors. There are two types of linear resistors

Fixed
Variable.

Fixed resistor

Fixed resistors are designed to set the right conditions in a circuit. Their values should never be changed to adjust the circuit since those were determined during the design phase. It can have a carbon composition or chip-and-wire wound type. It can also be made with a mixture of finely ground carbon or be very small in size and for high power rating.

These resistors have a specific value and these values cannot be changed.

Following are the different types of fixed resistors

Carbon composition resistors
Wire wound resistors
Thin film resistors
Thick film resistors

Variable resistor

Variable resistors have fixed resistor elements plus a slider. The slider taps onto the main resistor element so there will be three connections; two are connected to the third element and one to the slider.

These resistors do not have a specific value and the values can be changed with the help of dial, knob, and screw. These resistors find applications in radio receivers for controlling volume and tone.

Examples of this are potentiometers, rheostats, trimmers, and so on.

Following are the different types of variable resistors

Potentiometers
Rheostats
Trimmers

Non-Linear Resistor

Non-linear resistors are those types of resistors where the electric current flowing through it changes with the exchange in applied voltage or temperature and does not change according to Ohm’s law. Or The resistor values change according to the temperature and voltage applied and is not dependent on Ohm’s law. Following are the different types of non-linear resistors

Thermisters
Varistor Resistors
Photo resistors
Surface Mount Resistors

Thermistors

Thermistors are a type of variable resistor that notices the change in temperature. In other words, it is a 2 terminal device that is very sensitive to temperature. The Resistance of a Thermistor is inversely proportional to the temperature.

Varistor Resistors

A varistor is a non-linear resistor made of semiconductor and current through which depends non-linearly on the applied voltage across it. MOV or metal oxide varistor is the most commonly used form of Varistor Resistors.

Photo Resistor or LDR (Light Dependent Resistors)

Photo Resistor or LDR (Light Dependent Resistors) or Photo Conductive Cell is a light-controlled variable resistor. The photo resistor resistance decreases with increase in incident light intensity.

Surface Mount Resistors

Surface Mount Resistors also called SMD resistor are rectangular in shape. An SMD is an electronic component that is made to use with SMT or Surface Mount Technology.

How Do Resistors Work?

Wiring a resistor in a circuit will reduce the current by a precise amount. If you look at resistors from the outside, they most likely look the same. However, if you break it open, you’ll see an insulating ceramic rod running through the middle with copper wire wrapped around the outside. Resistance depends on those copper turns. The thinner the copper, the higher the resistance since it’s harder for the electrons to pass through it. As we’ve found out, it’s easier for the electrons to flow in some conductor materials than insulators.
George Ohm studied the relationship between resistance and the size of the material that was used to make the resistor. He proved that the resistance (R) of a material increases as its length increases. This means that the longer and thinner wires offer more resistance. On the other hand, resistance decreases as the thickness of wires increases. Having said that, Georg Ohm came up with an equation that explains this relationship

where ρ = resistivity (Ω-m)
Note: Conductors have much lower resistivity than insulators. At room temperature, aluminum comes in at about 2.8 x 10-8 Ωm, while copper is significantly lower at 1.7 x 10-8 Ω-m. Silicon has a resistivity of about 1000 Ωm and glass measures about 1012 Ωm. Resistivity varies for different materials.

Resistor Color Coding

4-Band Color Coded Resistor

For a four-band color coded resistor, the 1st and 2nd band represent the 1st and 2nd significant digit while the 3rd band represents the multiplier, and the 4th band represents the tolerance.

5-Band Color Coded Resistor

For a five-band color coded resistor (high precision resistor), the 1st, 2nd and 3rd band represent the 1st, 2nd and 3rd significant digit while the 4th band is the multiplier and the 5th band is the tolerance.

For some four-band color coded resistor, another extra band (5th band) indicates the reliability in percent of failures per 1000 hours (1000h) of use.

Resistor Color Coding Table

Resistor Power Rating

Everytime a current passes through a resistor due to the presence of a voltage across, electrical energy is lost in the form of heat. The greater the current flow, the hotter the resistor will be. A resistor can be functional at any combination of voltage and current as long as it does not exceed the power rating that a resistor can convert into heat or absorb without any damage.

Resistor Power Rating is defined as the amount of heat a resistor can handle without sacrificing its performance in no definite time. In Ohm’s law, when a current flows through a resistance, a voltage is dropped across it producing a product that relates to power. In other words, if resistance is subjected to a voltage, or if it conducts a current, then it will always consume electrical power. Given this, we can say that these three quantities– power, voltage and current, are in a power triangle.

Using the Resistor Power Triangle is the best way to calculate the power dissipated in a resistor if we know the values of the voltage and current across it. Additionally, Ohms law allows us to calculate the power dissipation given the resistance value of the resistor. We can obtain two alternative variations of the above expression for the resistor power if we know the values of at least two among the three– voltage, current, and resistance.

Based on the power triangle, the electrical power dissipation of any resistor in a DC circuit can be calculated using one of the following three standard formulas:

P= V×I

P=I²×R

P=V/R

where V is the voltage across the resistor in Volts,

I is current flowing through the resistor in Amperes, and

R is the resistance of the resistor in Ohmss (Ω).

Types Of Resistor Materials

Below are different types of resistor materials, their pros and cons, and their uses

Carbon Composite

Carbon Composite is made up of a mixture of fine carbon particles and a non-conductive ceramic material pressed in a cylindrical shape and baked. The resistance value depends on the dimensions of the body and the ratio between carbon and ceramic material. The more carbon you add, the lower the resistance. Carbon composition resistors are remarkably reliable but have poor accuracy with a maximum tolerance of around 5%.

Carbon Film

Carbon Film is a pure carbon film enclosed in an insulating cylindrical core, cut in a spiral to increase the resistive path. It is more accurate than carbon composite. However, in applications that require high pulse stability, special carbon film resistors are used.

Metal Films

Metal Films are produced with tantalum nitride but more often, they are made using Nichrome. A combination of ceramic and metal is used as the resistive material. It has better stability, temperature coefficient, and tolerance than carbon films. Typical tolerances are between 0.5% and 2% with a temperature coefficient between 50 and 100 ppm/K. Stability is lower than wire-wound, but its high-frequency properties are better.

Wire Wound

Wire Wound is created using a winding resistance wire that has a spiral non-conductive core. The resistance wire is made up of nickel-chromium and the core is ceramic or fiberglass which has a coating protected with vitreous enamel. It is not suitable for applications higher than 50kHz since the spiral winding has capacitive and inductive effects. It is best used for high precision or for high power applications.

precision resistor

A precision resistor is a thin bulk metal foil that is cemented on a ceramic substrate. It is the most accurate and stable type and it features a very low-temperature coefficient of resistance that is used for applications with high precision requirements.

Metal Oxide Film

Metal Oxide Film. Unlike the metal film, its resistive material is usually a metal oxide such as tin oxide. It is useful in applications requiring higher endurance because it has a higher operating temperature that makes it more reliable and stable.

Uses of Resistor

We know that one of the main uses of resistor is to control the flow of current. In a resistor, electrons have a collision with ions which slows down the flow of electricity and lowers the current and also produces heat. If a resistor is said to have high resistance then it means less current flows in it for the given voltage.

Some applications and uses of resistor are listed below

Circuit functions
Dividing voltage
Heating
Frequency and timing
LEDs and transistor

Resistor usage in Circuit Functions

There are various types of resistors that work according to the usage range. In that, we can set the resistance by using a knob kind of feature. Changing resistance will affect the flow of current inside the circuit. For example, this type of resistor is used in controlling the speed of a motor, pitch of a musical tone, loudness of an amplifier, etc.

Resistor is used for Diving Voltage

Dividing the voltage works when some components need to work in a much lesser voltage than the supplied input voltage. Connecting the resistors in a series will help to drop the voltage across each resistor equally, thus, assisting the appliances smoothly which works in those conditions.

Resistor is used for Heating

Because of the nature of generating heat when conducting current, resistors are used in a heater, toaster, microwave, electric stove, and many more heating appliances. In a light bulb, the metal filament glows white-hot due to the very high temperature produced from the resistance when electricity is passed through it.

Uses of Resistor to function in particular Timing and at a certain Frequency

Like in a light flasher, electronic sirens, blinking lights used in airplanes or tall towers which acts as a collision avoidance measure. They work on the principle of filling up current to a certain time and then discharge light, in here, the resistor decides how much current has to be passed according to the time allotted. If resistance increases, the time for discharging current in the circuit increases.

Resistors used in LEDs and Transistors

Too much current passed inside a LED or transistors can be dangerous because they are very sensitive to electric current. The use of a resistor in the circuit will help the LEDs and transistors and other types of semiconductors to function in the desired current range ideal for them

Applications of Resistor

Wire wound resistors find application where balanced current control, high sensitivity, and accurate measurement are required like in shunt with ampere meter.
Photo resistors find application in flame detectors, burglar alarm, in photographic devices, etc.
Resistors are used for controlling temperature and voltmeter.
Resistors are used in digital multi-meter, amplifiers, telecommunication, and oscillators.
They are also used in modulators, demodulators, and transmitters.

What is a resistor, used and Applications