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Passive Components: Resistors, Ohms Law, and Capacitors
Chapter 4

For me, the machine is above all an instrument that permits me to be poetic. If you respect the machine, if you enter into a game with the machine, then perhaps you can make a truly joyous machine -- be joyous, I mean free.
~Jean Tinguely (1925-1991)

Question: Can you limit or vary the number of electrons that pass a point in a given period of time?

Because many electronic devices are sensitive to too much current and voltage, resistors will be the primary devices you use in limiting the current and voltage flow entering your sensitive electronic parts.


Resistors are devices that are composed of materials that cause an electrical resistance. They are used for current control because they limit the passage of electrons and cut down on voltage pressure.


Close-up of a carbon resistor laying on a circuit board. 3D model by Todd Swepston


Resistors function by limiting or resisting the passage of electrons, and in this process, they cut down on current pressure, which protects the parts.

Resistors can have a single fixed value or they can be variable. Variable resistors allow you to change the resistance by turning a dial or moving a knob (directly below). Variable resistors are very common, and each time you turn the knob on your stereo you are varying the number of electrons pushing on your speaker to pump up the volume or TURN DOWN THAT NOISE!

A photo resistor resistance changes in relation to the amount of light it is exposed to. Photo resistors can be used in creating circuits that are triggered by passing shadows.


Variable resistor. Here you would hook the middle leg and one of the outside legs into a complete circuit to get the variable resistance.3D model by Jessica Miller.

A photo resistor changes resistance in relation to the varying light levels it receives. Note: Photo resistors are semiconductors and therefore not passive. More in chapter 5  3D model  Michael Tanzillo.


Resistors receive electrons from a voltage source based on voltage pressure and they function by not allowing all of the electrons that enter into the resistor to pass out of the resistor in a given period of time.

As electrons are pushed through a resistor by a force of voltage like a battery, some of the electrons randomly collide with the atoms within the resistor, which creates heat. These mini collisions within the atoms cause vibrations, and these vibrations are passed to air molecules in the form of heat. This is one reason why electronic components are often hot, and why electronic cases have holes that allow the excess heat to escape.

This will also give you the first design clue for creating your own project and invention. Make sure the electronics in your project have access to circulating air so the heat created in the process of electrical resistance can pass out of the container.

Many resistors are composed of carbon and a glue-like binder, though there are many other types of resistors made from different materials such as coiled wire and film. Other classes of resistors are selected based on the characteristics of their ability to absorb heat and remain stable, to resist moisture, or to resist solvents. Some resistors are designed for special high power applications.


Visualization of electron flow in a resistor that is attached to a voltage source--many electrons enter and fewer come out.


In a carbon resistor, you can increase or decrease the resistance by choosing a resistor that increases or decreases the amount of carbon in relation to the glue-like binder. Carbon is the conductive molecule in this material mix.

Even the graphite lead in your 2B pencil is a carbon resistor, and some artists have exploited the resistive qualities of lead pencils in the creation of art. The artist Diana Burgoyne has created variable sound drawings that allow participants to change the tone and frequency of a speaker by using a common lead pencil to reconfigure the length and path of a sound circuit.