Summer 2002 Tech Stuff
Part 1
Home / Features / Electrix
 Practical Basic Electricity 1
 Volts, Ohms and other vices
 By Dave Clements
Every class I have attended, and every book I have read, always starts off with What is Electricity? So I guess I'll follow suit. When I took my first automotive electricity class, they said that the practical technician looks at electricity as an invisible force that flows from positive to negative. Then the next class explained that all matter is composed of atoms with protons neutrons and electrons and that electrons flowed from negative to positive. I was starting to be a little confused after a few more classes and books. I decided that the theory changes every few years, so maybe the first view was probably a good way for people, who just want to make it work without letting the smoke out, to look at it. Current theory is that electrons flow negative to positive and the packets of energy necessary to move the electrons flows positive to negative. So for the rest of this class I am arbitrarily going to use the theory that was around when our bikes were new. Electricity is an invisible force that flows from positive to negative and can be thought of as behaving much like water in a garden hose. 

What ever it is, we can describe how it behaves and how it will behave under any situation with mathematical formulas. But first, the common terms.

In this series I will try to demystify electricity, and even get into some electronics toward the end. I will try to keep the math to a minimum, but it is very difficult to describe electricity with out some. I will try to keep the emphasis on the practical side.  When there is the opportunity, I will explain the text book approach, plus all the backyard fixes that I know of. With all that said, let's jump right in with both feet.


Basic Electricity Terms (with Garden Hose Equivalents)

Volt which describes the electromotive force of the electricity (you can think of voltage as water pressure).

Ampere which describes the intensity or rate of flow of the electricity (you can think of amps as the size of the garden hose).

Resistance which is anything that slows or stops the flow of the electricity (you can think of resistance as someone bending the hose to slow or stop the flow you will find resistance referred to as impedance also).

Watt which is the unit of power (you can think of watts as the amount of water that flows out on the ground).

Before all of these you may see: 

Kilo- for 1000 
Mega- for 1,000,000 
milli- for 1/1,000 
micro- for 1/1,000,000 

I.E. your electric bill will be in kilowatts, or you may need to measure milliamps.

Although there are literally thousands of formulas, I only try to remember two: Ohm's Law and the Power Formula. You can deal with most anything built before 1980 (except radio and TV) with these two formulas. The first, Ohm's law, states that E = I x R  (Or, electromotive force in volts = intensity in amps, times the resistance). So those of you that are good at math games already know that we can change it to read R = E/I or I = E/R. That first class back in the sixties taught it as a magic circle, with E over I x R and you just took the one you wanted to know out of the circle and did what was left . I.e. If you want to know amps, you take the I out which leaves  E/R, so you divide the volts by the resistance to find the amps. 

The power formula states that P = E x I or Power (in Watts) = Volts times Amps. It can also be remembered as a magic circle.

Why do we need to remember these? Suppose that you just added two driving lights that you bought on Ebay. What size wire are you going to run? What size fuse? 

Simply plug the resistance that you measure in to Ohm's Law and solve. More on this later -  I’m getting ahead of my self. You may see these written with different symbols, depending upon when a book was written, but this is the way it was taught when my Scout was new. We will get back to formulas later. Now I want to go into electricity’s alter ego.

Ohm's Law:
E = I x R

Power Formula:
P = E x I

Click to view full size
Magic triangle or circle
(click for full-size view with 

Magnetism is the force possessed by some materials which enables them to attract or repel certain other materials. Magnets fall into two broad categories: 'natural', like lodestone, and 'artificial', which are magnetized by outside forces. Artificial magnets may further be classed as 'permanent' and 'temporary'. Permanent magnets are made of iron or an alloy or even a ceramic that retains its magnetism for a long time. Temporary magnets are magnets because they are in contact with a magnet, or were recently in contact with one. All magnets have two poles, a north and a south. The theory is that the molecules align with their poles at the same end as the whole.
Click to view full size
Arrangement of molecules in 
steel bar before and after 
being magnetized
Any magnetic material which has been magnetized will always retain some of its magnetism, even though in the case of temporary magnets most of the magnetism is lost once the source of magnetism is removed. This is called residual magnetism. (We’ll see more on this when we get into generators.)  The area around a magnet that exerts magetic force is called the magnetic field, and is composed of lines of force that go from the north pole to the south pole (or the south to the north depending on which theory we are using this week). If you place a piece of paper over a magnet and sprinkle iron filings over it, you can see the lines of force.

The strength of the magnet varies with the number of lines of flux. With more lines equaling more force. Permeablity is the ablity to transmit lines of flux. Iron, steel, and nickel have a very high permeablity, sometimes as high as 100, while materials like air, wood, paper (non magnetic stuff) and brass have a permablity of 1 (why 1 instead of 0? Because the field still exists in them, it just isn't changed). When a piece of material such as iron, with a permeablity higher than 1, is brought into a magnetic field, the lines of force are diverted, and pass through the material because of the permablity. It then becomes a magnet. This is called magnetic induction; all artificial magnets are made this way. 

We’ll get into electromagnets and some basic test equipment next time.

Click to view full size
Magnetic flux lines illustrated 
with iron filings.
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