Learn the working, types, important formulas, series and parallel connections, and practical applications of resistors.
1. Introduction
A resistor is a fundamental passive electrical component that opposes the flow of electric current. Resistors are used to control current, divide voltage and protect electronic components.
When two or more resistors are connected together, they form a resistor network. Such networks are commonly arranged in series, parallel or series-parallel combinations.
2. What Is a Resistor?
A resistor provides electrical resistance, which is measured in ohms (Ω). It dissipates electrical energy in the form of heat.
Controls current flowing through a circuit.
Produces required voltage levels.
Helps prevent excessive current in components.
1 kΩ = 1,000 Ω
1 MΩ = 1,000,000 Ω
3. Ohm’s Law
Ohm’s Law states that current through an ohmic conductor is directly proportional to the applied voltage, provided physical conditions such as temperature remain constant.
Other forms are: I = V/R and R = V/I.
I = V/R = 12/6
4. Types of Resistors
Has a specified resistance value. Examples include carbon film, metal film and wire-wound resistors.
Its resistance can be adjusted. Examples include potentiometers, rheostats and trimmers.
Resistance depends on external conditions. Examples include thermistors, LDRs and varistors.
5. Resistor Networks
A resistor network consists of interconnected resistors arranged to obtain a required equivalent resistance or to distribute voltage and current.
5.1 Series Connection
In a series connection, resistors are connected along a single current path. The same current passes through each resistor.
Req = 2 + 4
5.2 Parallel Connection
In a parallel connection, resistors are connected between the same two nodes. The voltage across each resistor is equal, while current divides between the branches.
For two resistors:
Req = (6 × 3)/(6 + 3) = 18/9
5.3 Series-Parallel Connection
A series-parallel network combines series and parallel resistor arrangements. It is simplified step by step by calculating the equivalent resistance of each section.
6. Series vs Parallel Resistors
| Parameter | Series | Parallel |
|---|---|---|
| Current | Same | Divided |
| Voltage | Divided | Same |
| Equivalent Resistance | Sum of resistances | Less than the smallest positive branch resistance |
| Main Use | Voltage division | Current division |
7. Power Dissipation in Resistors
A resistor converts electrical energy into heat. Its power rating must be sufficient for the expected power dissipation.
P = 102/100 = 1 W. The resistor must have an appropriate power rating and thermal margin.
8. Applications of Resistors
- Current Limiting: Used in LED and electronic circuits.
- Voltage Dividers: Generate required voltage levels.
- Current Measurement: Shunt resistors help measure current.
- Biasing: Establish operating conditions of transistors.
- Sensor Circuits: Used with thermistors and LDRs.
- Heating: Resistive elements convert electrical energy into heat.
9. Conclusion
Resistors are essential components used to control current, divide voltage and dissipate electrical energy. Resistor networks provide different equivalent resistance values through series, parallel and combined connections.
Understanding Ohm’s Law, series and parallel resistance, and power dissipation builds a strong foundation for electrical circuit analysis and electronic engineering.