Passive Components: Resistors and Capacitors

Beginner Time: 20 min Type: Concept Focus: Controls / Panel Design

After this module: Understand resistors, capacitors, and inductors — their ratings, stored energy, and behavior in DC and AC circuits.

Prerequisites: Electrical Quantities and Circuit Language

Purpose

This module explains the basic practical behavior of two common passive components used throughout electrical and control work.

Resistors

Resistors are used to:

limit current
create intentional voltage drop
bias signals
form dividers and timing networks

Key practical checks:

resistance value
power rating
tolerance
heat generated in use

Capacitors

Capacitors store charge between two conductors separated by an insulating dielectric.

Common uses:

smoothing and filtering
timing
energy storage
noise suppression

Component families

Common resistor families:

carbon or film types
metal film
wire-wound

Common capacitor families:

ceramic
film
electrolytic

Different families trade size, stability, voltage capability, and failure mode differently.

Practical cautions

Electrolytic capacitors are polarity-sensitive.
Capacitors can hold hazardous stored energy after power is removed.
Resistors fail from heat as often as from wrong resistance value.
Real components are not ideal; tolerance and temperature matter.

Working takeaway

For both parts, value alone is not enough. Always check:

the electrical job
the physical part family
the rating
the failure consequence

NFPA 79-2024, Chapter 7 — Protection against electric shock
IEC 60204-1:2018, Clause 6 — Protection against electric shock

← Electrical Equations Reference ↑ Electrical Fundamentals Diodes, Transistors, and Switching Basics →

Trust Boundary — Engineering Judgment Required

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