Resistors

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 are coiled around a ceramic rod and the outer part of the resistor is coated with an insulating paint.

The SI unit of resistor is Ohm.

➤

History

The Resistance was discovered by the year 1827 from Georg Simon Ohm, a German electrician. Ohm was born in Germany, in the city of Erlangen at 1787 and died at 1854.
Georg Simon Ohm noticed that different materials that are considered as electrically conductive, will not allow the current to flow within their body with the same ease. The difficulty that each material had, had to do with some parameters such as the type of the material and some external factors such as the temperature or the humidity of the atmosphere.
G.S.Ohm described this behavior and gave the name "Resistance". He then announced the Ohm's law that connects the resistance with the voltage and the current af follows:

➤

How Does it work and Applications

Circuit functions - Resistors are used to control current flow in circuits. This configuration is typically helpful for managing circuit tasks like altering the motor’s speed, the pitch of a musical note, the amplifier’s volume, etc. In electronic circuits, resistors provide a range of functions, such as reducing current flow, regulating signal levels, dividing voltages, biassing active components, and terminating transmission lines.

Voltage dividers - As voltage dividers, resistors are utilised in electrical circuits. A voltage divider distributes the source voltage among various electrical circuit components and provides the required operating voltage at the load terminal or output.

Heating applications - The Joule's law of heating states that heat is inversely proportional to resistance. Adjusting the current and time variables can be utilised to alter the temperature. Temperature sensors typically employ thermistors. The resistance value of these resistors varies with temperature. Thermistors are made up of metal oxides.

Variable resistors - Since the resistance of variable resistors can be adjusted to a certain value, they are frequently employed in electrical circuits to change the value of current or voltage. With variable resistors, you may change the resistance while maintaining a constant current to change the voltage value. Variable resistors come in two different basic varieties: potentiometers and rheostats. Your radio’s volume control is an illustration of a potentiometer, and your car’s dash light dimmer is an illustration of a rheostat.

Frequency and timing - Devices such as light flashers, electronic sirens, and blinking lights on airplanes or towers operate by storing electrical charge for a specific duration and then releasing it as light. In these cases, the resistor determines the amount of current that flows based on the predetermined time. By increasing the resistance, the discharge time of current in the circuit is prolonged.

LEDs and transistor - LEDs and transistors are examples of semiconductor devices that are sensitive to input current values. As a result, resistors are utilised in the circuit to control the input current value.

➤

Different Type of 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 resistors: 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
- hick film resistors
Variable resistors: 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. Following are the different types of variable resistors:
- Potentiometers
- Rheostats
- Trimmers

Non-linear resistors
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
Varisters
Photo resistors

➤

Electronic Symbol and Notation

➤

How to read the resistor value with illustration

4-Band Resistor Color Code
The first two bands on a 4-band resistor represent the first and second digits of the resistance value. The third band represents the multiplier, and the fourth band represents the tolerance.

Here are the steps to follow when reading 4-band resistor color codes:
1. Identify the first two bands’ colors and their corresponding values using a resistor color code chart (see left figure).
2. Determine the multiplier using the third band’s color, which represents the number of zeros that follow the first two digits.
3. Calculate the resistance value using the following formula:
  Resistance (Ω) = (1st digit value x 10 + 2nd digit value) x Multiplier
  Next, determine the tolerance by identifying the fourth band’s color. The tolerance represents the resistor’s allowable deviation from the specified resistance value.

5-Band Resistor Color Code
The first three bands on a 5-band resistor represent the first, second, and third digits of the resistance value. The fourth band represents the multiplier, and the fifth band represents the tolerance.

Here are the steps to follow when reading 5-band resistor color codes:
1. Identify the first three bands’ colors and their corresponding values using a resistor color code chart.
2. Determine the multiplier using the fourth band’s color, which represents the number of zeros that follow the first three digits.
3. Calculate the resistance value using the following formula:
  Resistance (Ω) = (1st digit value x 100 + 2nd digit value x 10 + 3rd digit value) x Multiplier
  Lastly, determine the tolerance by identifying the fifth band’s color.

6-Band Resistor Color Code
The first three bands on a 6-band resistor represent the first, second, and third digits of the resistance value. The fourth band represents the multiplier, the fifth band represents the tolerance, and the sixth band represents the temperature coefficient. Here are the steps to follow when reading 6-band resistor color codes:

Here are the steps to follow when reading 6-band resistor color codes:
1. Identify the first three bands’ colors and their corresponding values using a resistor color code chart.
2. Determine the multiplier using the fourth band’s color, which represents the number of zeros that follow the first three digits.
3. Calculate the resistance value using the following formula:
  Resistance (Ω) = (1st digit value x 100 + 2nd digit value x 10 + 3rd digit value) x Multiplier
  Next, determine the tolerance by identifying the fifth band’s color. Finally, determine the temperature coefficient by identifying the sixth band’s color. The temperature coefficient represents the resistor’s change in resistance as the temperature changes.

➤

Examples of Reading Resistor Values

➤

References

BYJU'S. (NA). Resistor. https://byjus.com/physics/resistor/
Lazaridis, G. (2009). The Resistor. https://pcbheaven.com/wikipages/theresistor/
testbook. (2023). Uses of Resistors: In Circuit, Voltage Dividers, LEDs, Transistors & Daily Life. https://testbook.com/physics/uses-of-resistor#:~:text=In%20electronic%20circuits%2C%20resistors%20provide,heating%20applications%20and%20many%20more.
ConceptDraw Solutions. (NA). Electrical Symbols — Resistors. https://www.conceptdraw.com/How-To-Guide/resistors-symbols.
Sharda A. (2024). How To Read Resistor Band Colors (4, 5, and 6 Bands). https://digitalbunker.dev/how-to-read-resistor-band-colors-app/
Stockpole Electronics Inc. (NA). Resistor Color Code Calculator. https://www.digikey.ph/en/resources/conversion-calculators/conversion-calculator-resistor-color-code