Calculating Resistance in Series and Parallel

Circuits

- Basic Formulas for Rapid Computation of Circuit

Resistance

Introduction

- Informational lecture by Fred Baker
- Electronics Instructor for U.S. Navy

Topics of Discussion

- Resistance totaling values, dependent on the

circuit structure - Knowing how to calculate resistance depending on

circuit structure - Understanding these basics can save valuable time

and effort

Resistance Rules for Series Circuits

- Series circuits are always one-for-one additive
- Rt R1 R2 R3 Rn

Series Circuit

- Sample of a Series Circuit layout

R1

R2

R3

Solving for Series Resistance

- Calculate the resistance using the series

formula - Rt R1 R2 R3 Rn
- Rt 20W 30W 50W 100W

R120W

R230W

R350W

Resistance Rules for Parallel Resistance Circuit

- Parallel circuits are reciprocally additive
- Rt

1 1 1 1 R1 R2 R3

Parallel Circuit

- Sample of a Parallel Circuit layout

R120W

R230W

R350W

Solving for Parallel Resistance

- Calculate using reciprocal formula
- Rt 1 / 1/R1 1/R2 1/Rn
- Rt 1/1/20W 1/30W 1/50W
- Rt 1/0.05W 0.033W 0.02W
- Rt 1/103W 9.70W

Summary

- Determine the type of circuit layout you are

working with - Apply the correct formula
- Verify answer by double-checking math