Chapter 1 - Resistors

Chapter 1: Resistors

Contents

  • Introduction

  • Resistor Units

  • Schematic Symbol

  • Fixed Value Resistors

  • Variable Resistors

  • Characteristics of Resistor

  • Resistor Color Code

Introduction

  • A resistor is an electrical component that limits current flow in a circuit.

  • Resistance: Defined as the opposition to the flow of electric current.

Resistor Units

  • Electrical resistance measured in ohms (Ω).

Schematic Symbol

  • Resistors have two terminals for connections.

  • Schematic symbols for resistors:

    • International-style

    • American-style

Fixed Value Resistors

  • These resistors maintain a stable value within specified limits.

  • Types include:

    • Carbon Composition

    • Carbon Film

    • Metal Film

    • Wire-wound

Summary of Fixed-value Resistors

  • Carbon Composition: Accurate and stable over time and temperature.

  • Carbon Film: Accurate, not frequency sensitive.

  • Metal Film: Cheaper, more stable than carbon composition.

  • Wire-wound: Cheap, not frequency sensitive, widely available.

Advantages and Disadvantages

  • Carbon Composition: Expensive, frequency sensitive, not high ohmic.

  • Carbon Film: Price between carbon composition and wire-wound, value changes with time.

  • Metal Film: High accuracy but more expensive.

  • Wire-wound: Good for performance under temperature and humidity variations.

Variable Resistors

  • Resistors whose value can be externally adjusted.

  • Types include:

    • Potentiometer

    • Rheostat

    • Preset

Potentiometers

  • A three-terminal resistor, adjustable by rotating a knob or using a slider.

Applications of Variable Resistors

  • Used in audio equipment for volume control, and in light dimmers.

Characteristics of Resistor

  1. Power Ratings: Determined by construction and size, typical ratings include 1/8W to 5W.

  2. Tolerances: Specifies the acceptable range around nominal value, usually in percentage (1%-20%).

Tolerance Example

  • For a 4.7 KΩ resistor with a 10% tolerance: Maximum = 5170 Ω, Minimum = 4230 Ω.

Resistor Color Code

  • Used to determine the value of resistors based on color bands.

Examples and Practices

  • 4-band color codes provided for practice.

Summary

  • Understand schematic symbols for resistors.

  • Know common types and applications.

  • Identify values and ratings of resistors.