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Dominoes

The most beautiful thing we can experience is the mysterious.
~ Albert Einstein

Question: What is the nature of electron movement?

Imagine a metal doorknob, which has a great number of valence electrons circling the atoms and migrating from atom to atom individually and en mass—billions, trillions of electrons moving as waves of energy, rippling through and on top of a conductive material. You are walking toward the door, and as you shuffle across the rug, electrons push into your shoe from the friction of your shoe moving on the rug. These electrons now migrate to your clothing and your body, and as you touch the doorknob, your much higher electron count is now discharged. Ouch!

Current is the movement of electrons on the surface of and through conductors. The flow of electrons through the material is proportional to the mass of the conductive material, and the density of electrons available.

 

Visualization of Electron flow through wire. 3D model by Mike Tanzillo

 

To establish a workable relationship with electron flow we must first establish a way of counting the numbers of electrons flowing past a point in time. 6,250,000,000,000,000,000, or 6.25 X 10 to the 18th, is (roughly) the number of electrons in one amp of current. These quantities can be measured in a number of ways, one of which we will explore in the lab of this chapter.

Copper is a very common conductor with a high density of electrons, and a little electrical resistance. As one or more electrons are pushed to a new atom, the atom it jumps onto becomes a negative ion, which causes it to shed an extra electron and the electrons jumps from atom to atom, down the wire.

In order to move electrons through a wire, pile a bunch of electrons at one end of the wire and create a closed loop circuit. This volume of electrons can come from a battery or a wire connected to larger quantities of electrons. From here, the electrostatic charges of the electrons create an electromotive force (EMF) that repels the electrons in the wire. You can also imagine dominoes knocking each other down one by one. The dominoes do not move along the floor, but they effect a flow of energy rippling through the dominoes, just as current can be thought of as a rippling flow of electrons through a wire.

Metal wire is a good conductor because the metal atoms have valence electrons, which support conduction. Valence electrons are the ones least attracted by the nucleus of the atom and have the potential to move from atom to atom. While wire is a good conductor, it also presents friction to electrons that are pushing through the metal. As the electrons are flowing, some crash into protons and slow the flow down.

A thick wire would naturally have more valence electrons available for conduction of electron flow than a thin wire. Clearly, the width of the wire affects the possible rate of conduction.

Walter De Maria created an artwork that allowed the static charge generated in turbulent rain clouds to be discharged into the earth through a grid of stainless steel rods. The Lightning Field is 400 polished stainless steel poles, two inches in diameter, installed in a grid array, one mile by one kilometer in width. The poles act as invitations to lightning. [1]

 

 

The Lightning Field by Walter De Maria, 1977. Stainless steel rods, lightening and friction from rain clouds in
Southwestern New Mexico. Image complements of Cranberries on Flickr

 
 Horizontal Lighting in Vienna Austria by Adrian Fernandez

 

A good way to visualize the relation of wire width to current flow is to picture a wide pipe with massive amounts of liquid trying to pass through in a period of time. Now, imagine massive amounts of liquid trying to push its way through a thin pipe. You can visualize that the pressure of all the liquid/current on the thin pipe/wire may cause the pipe or wire to burst or to heat up. The wire can heat up and may become molten, breaking the circuit. This burnt out wire may now protect more sensitive parts of the circuit connected to and beyond the broken wire.

 

Electrons cascade through wire like marbles bumping up against each other, but we need to push on the electrons with some electromotive force. This is a cross section and in order for electrons to move, you need a complete circuit.


We have just described a fuse. A fuse is designed to burn up and disconnect if too many electrons are pushed through a the thin wire. The pressure of the electrons pushing through the wire is so great that it heats the metal and melts it, protecting the more sensitive circuitry within. A fuse also tells you, intuitively that the thickness of a wire is related to its ability to support current flow. If you do not use wire that is thick enough, then there is a good chance your electronic parts can be damaged, or worse, a fire can result.

Intuition is a fantastic way to get a sense of current flow, but in order to accurately measure current, we must look at actual numbers.