## What is a Resistor?

The resistor is the first electrical component you will encounter as a student. Yet, this is a surprisingly difficult question to answer in the age of AI. Those powerful tools can provide you with facts and application far beyond what we can accomplish in this short article. Yet, I wonder if we can answer in a meaningful way, a narrative beyond the cold facts and figures provided by the AI.

Let’s find out by exploring the journey of an emerging electronics technologist as they encounter resistors in their studies.

## First encounters with the resistor

On the first day in the very first lab, our hero is presented with resistors. On the surface, the lab is simple – construct a complete circuit and measure the resulting current and voltage followed by a brief introduction to Ohm’s Law.

Yet, this lab is surprisingly frustrating and consumed several hours. The real objective is to form a mental image of this abstract concept know as electronics. It a challenging concept because it can’t be meaningfully interpreted by any of our human senses. With the possible exception of using resistors as a window into the operation of the circuit.

Tech Tip: As an educator you can bring this abstraction to life. Use light bulbs as resistors. Alternatively, use higher power resistors allowing students to feel the heat generated by the resistor. For some added fun, add small motors to the lab. A series connected motor with an appropriate light bulb provides a highly visible interactive lab.

## A resistor mesh

Later in the semester after our hero has mastered series and parallel resistive circuit, nonconforming resistive circuits that are neither series nor parallel are encountered. Our hero has a visceral epiphany that algebra is important. Those “simple” algebraic rules of Ohm’s law coupled with Kirchhoff’s fundamental circuit laws guide our hero’s pencil to produce mesh and nodal equation. The level of circuit abstraction is beyond comprehension for the beginner, but nothing like what is coming next.

Tech Tip: Many students struggle with the direction of current flow in the mesh circuits. Instead of attempting to get the first estimate (direction) correct, it can be beneficial to make the mesh and nodal analysis algorithmic. For example, make all current loops flow in a clockwise direction. Likewise, assume all current leave a node. IMO this speeds up the process and gets all students on the same page increasing the classroom collaboration.

## The reactive struggle when resistors are combined with capacitors and inductors

Up until now, the circuits have been static with a constant DC voltage for all circuit elements. Not anymore, our hero encounters AC for the first time. Not just AC, but all the reactive AC components including capacitors and inductors. The level of abstraction pushes the limits of our hero. In fact, the concepts are so complex that the results are often described using calculus terms of time rate of change. The dependence on algebra increases significantly as the student relies on exponents and logarithms to solve for resistor values. As complex as this is, there is more to come.

Tech Tip: As an educator, you can select components that allow experiments to be carried out at a human rate. For example, a large capacitor can be charged via a resistor (RC timing lab) or a constant current power supply. In both cases, select the component values so that students can perform the calculation using a wall clock to signal data collection in 5 second increments. There is also something to be said for the discharge spark of a large inductor displayed directly or as the discharge though a neon lamp. Do be careful as these thousand-volt discharges can be painful and cause harm as anyone who has ever held the working end of a sparkplug wire knows.

## The calm before the storm with resistor application in op amps and digital circuits

As our hero’s journey continues with some relatively easy topics at least as far as resistors are concerned. This is a busy time as our hero learns about operational amplifier (op-amps), digital circuits, and microcontrollers. By comparison to previous work, this is easy. For example, the gain of an op amp is determined by the ratio of two resistors and variable resistors are used as volume controls. Digital circuits and microcontrollers use resistors as pullup or pull-down input signals. They also use resistors as current limiting devices to interface with output devices such as LEDs and transistor. This is a fun as our hero is constructing operational circuits that do interesting things.

## The storm with resistors in advanced analog circuits

The encounter with AC was challenging but now our hero must contend with filters and complex interactions with physical systems collectively known as controls. In the past our hero transitioned from DC to AC by upgrading a voltmeter for an oscilloscope. That oscilloscope is now upgraded to a spectrum analyzer. Intuitively our hero understands these physical phenomena such as using a variable resistor to boost a radio’s treble and bass. However, it comes as a surprise that a resistor may be used to model the shock absorber like those installed in a car’s suspension to dampen the car’s natural tendency to bounce. Equally surprising that the car’s mass may be modeled as an inductor and the spring as a capacitor.

### This is the defining moment for our hero.

The signals and system class is the highwater point in their education. If our hero can synthesize the physics, math, and electrical concepts, graduation is assured. The remaining education material is constrained to a capstone demonstration of accumulated knowledge and practice.

The hero’s journey which started by selecting the proper color codes has progressed to incorporate a vast body of advanced mathematics and physics. Yet the “simple” resistor remains a constant throughout the process.

To all my heroes, well done!

APDahlen

P.S. To learn more about resistors and how they are categorized I encourage you to visit this authoritative page. As a future resource be sure to bookmark and return to the DigiKey TechForum. Finally, search DigiKey for your electronics needs.

## About the author

Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.