Monthly Archives: November 2015

What is a Resistor and How Does it Work?

You may have some knowledge regarding the electrical components of the circuit boards within your many computing devices, but how deep does that understanding really go? The truth is, those of us who aren’t electrical engineers have a lot of trouble developing the proper contextual understanding to really conceive of what’s going on behind our touch screens. This article is here to help you on your quest towards developing that contextual knowledge:

Before we talk about resistors, let’s first lay out some ground rules: from an electricity standpoint, most material s fall into two basic categories: conductors, which allow electricity to flow through them , and insulators, which generally do not. That said, any material will conduct electricity if you hit it with enough voltage, including the air we breathe (consider lightning).

electricityThese circumstantial middle grounds make the concept of resistance so helpful. Resistance is the ease (or difficulty) with which something will let electricity flow through it. Now we can say that a conductor has low resistance, while an insulator has high resistance.

A resistor, in the context of electrical engineering, refers to a device used to allow for precisely controlled amounts of electrical resistance to be implemented into electrical circuits. Resistance is defined as the voltage in volts requires to make a current of 1 amp flow through a circuit. For example, if it takes 500 volts to make 1 amp flow, the resistance comes out to 500 ohms. This is known as Ohm’s Law.

How do resistors work? First we need to cover a little background info regarding the physics of electricity:

Electricity is the force that flows through materials carried by electrons. Materials that conduct electricity are materials whose chemical properties allow for electrons to flow freely through them. Metals, for example, are composed in such a way their atoms are locked into a very sturdy, crystalline structure. Their atomic makeup is solid and strong, but not very dense. This allows electrons to sometimes have space to flow between the atoms. Plastics, on the other hand, are composed of molecules that are bonded in such a way that electrons are fastened into their positions, making it harder for them to carry electric current.

wire woudn resistorIf a highly resistant material is hit with high voltage, a large proportion of that electricity will have to be converted into a different kind of energy, namely, heat. There are all kinds of advantages to be found in this phenomenon; old-school light bulbs, for example, work because a large amount of electricity is run through an extremely small wire called a filament. Because the filament is so thin, the electricity has trouble making it through the wire and instead is converted to heat; so much heat that it begins to give off light.

There are also variable resistors, which allow for the amount of electrical resistance to be modified by the user via a knob or dial. You’ve used one of these; this is the basic physics behind volume knobs on audio equipment.

For circuit boards, resistors comes as tiny units that supply precise amounts of resistance when wired in. From the outside resistors look like small, short tubes that can be wired into a circuit at the front and back. Inside, there is a ceramic rod running through the middle with copper wire wrapped around the outside. A resistor like this is described as wire-wound. The number of times the copper wire is looped around the outside and the thinner the copper, the more resistance is supplied. Another design replaces the copper winding with a spiral pattern of carbon. They’re a cheaper option for lower-power circuits.