A passive electrical component with two terminals is used to limit or regulate the current flowing in an electrical circuit. Purpose: The main purpose of a resistor is to reduce the current and lower voltage in a particular part of a circuit. It is made of copper wires wrapped around a porcelain rod and the outside of the resistor is coated with insulating paint.
Types Of Resistor
Two basic types of resistors are given below:
- Fixed Resistor
- Variable Resistor
Fixed Resistor
These resistors have a specific value and these values cannot be changed. The different types of fixed resistors are:
- Carbon component resistors
- Wire resistors
- Thin film resistors
- Thick film resistors
Variable Resistors
These resistors have no specific values and values can be changed using knobs, and screws. These resistors are used in radio receivers to control volume and tone. The different types of Variable resistors are:
- Potentiometers
- Rheostats
- Trimmers
Characteristics / Features Of Resistor
- Long term stability
- Temperature coefficient
- Material resistive
- Electric noise
- Maximum voltage
- Failure rate
- Carbon Film Resistor
- 4-band Resistor
- The value of the resistor changes according to the selected parameter
- Nominal power varies according to the selected parameter
Color Coding
Resistors may not display their value to the outside, but their resistance can be calculated by their color pattern. PTH (plated through hole) resistors use the color coding system(which really adds flair to the circuit) and the SMD (Surface Mounted) resistor has its own value marking system. Here is a table with the color codes of the resistors:
| Color | Color code | Tolerance |
|---|---|---|
| Black | 0 | |
| Brown | 1 | ±1% |
| Red | 2 | ±2% |
| Orange | 3 | |
| Yellow | 4 | |
| Green | 5 | |
| Blue | 6 | |
| Violet | 7 | |
| Grey | 8 | |
| White | 9 | |
| Gold | – | ±5% |
| Silver | ±10% |
Resistor In Series and Parallel Combination
Resistor In Series Combination
Resistors are connected in series when the current flowing through all resistors is the same. These resistors are connected in series from end to end. The total resistance of the circuit is equal to the sum of all the individual resistance values.
Resistors in Series Formula
| Rt = R1 + R2 + R3 +……+Rn |
Here,
- Rt is the sum of all individual resistors
Resistor In Parallel Combination
Resistors are said to be in parallel when the resistor terminals are connected to two identical nodes. Resistors in parallel have the same potential difference between them.
Resistors in Parallel Formula
| 1/RT = 1/R1 + 1/R2 + 1/R3 +…..+ 1/Rn |
Here,
- 1/RT is the sum of the reciprocal of all individual resistors
Unit Of Resistor
The SI unit of the resistor is Ohm(Ω). An ohm is equivalent to a volt per ampere.
Applications
- Current limiting Resistor
- Generate voltage drop
- Pull up / Pull down Resistor
- Potential dividers
- To measure current as a shunt resistor