# Air vs. Water - Teaching Voltage

Discussion in 'General Electronics Chat' started by SullivanTrainingSystems, May 26, 2009.

1. ### SullivanTrainingSystems Thread Starter New Member

May 26, 2009
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Just wondering if anyone else out there uses compressed air as an analogy for voltage. My circumstances require me to teach electrical troubleshooting in a 5-day class, and all of my students know that hydraulic systems have pumps that provide "flow" instead of "pressure". I have always disliked the fluid analog because of this - so I use compressed air instead. Every kid has put air in a bicycles tire (hopefully), but none have typically had a hydraulics class or experience. Wondering is anyone agrees or has comments.

(BTW - Aside from the pump example failure, open valves and open switches are exactly opposite in their operation)

2. ### studiot AAC Fanatic!

Nov 9, 2007
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Not sure why you need the analogy.

Surely students approaching a course in electrical faultfinding know what current, voltage, resistance, power, etc are?

Apr 5, 2008
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4. ### thingmaker3 Retired Moderator

May 16, 2005
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I dissaprove of such models. They are inherantly innacurate. Ever have a leaky wire? Electricity spewing out of an open connection?

5. ### Wendy Moderator

Mar 24, 2008
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I've seen a lot of older TVs, both color and B&W, arc, while looking through the vents in the chassis. I would call that leaking electricity.

May 28, 2009
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The idea is to get someone with no experience in electronics to understand the basic properties of electricity, current, resistance and voltage. I've used those same techniques in my classes. For hands-on for example, I have them hold a 100 ohm resistor then touch the leads across a 9 volt battery to show them a fine example of Kirchoff's law of thermal radiation. When it heats up, they understand.

7. ### count_volta Active Member

Feb 4, 2009
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There is an excellent analogy.

A capacitor is a balloon. The air is charge. The air pressure is voltage. The speed with which air exits the balloon is current. Its completely analogous if you think about it.

A larger capacitor takes longer to charge, just like a larger balloon takes longer to inflate. This is the best way to explain voltage. I myself found it really hard to understand voltage at first. Potential energy can be a little confusing. Considering the fact that voltage is also indirectly the strength of your electric field, but in terms of joules it becomes really weird. But if you think of it as the pressure in a balloon it makes perfect sense.

Oh and the difference between a capacitor and battery would be an analogy between a balloon which has to be inflated manually vs a balloon that automatically refills itself with air as soon as all the air is gone out of it. What causes it to refill itself? Chemical reactions. But you can't have energy for free, so as soon as the chemical reactions die out, your balloon can't re-inflate itself, i.e. the battery is dead.

I am building a website that explains electricity for people who are not mathematically inclined, and yet interested. Kids, adults, etc. The layout of the website still sucks, but I'm working on it. Don't laugh too hard.

http://amazing-electricity.110mb.com/index.html

If I made any mistakes, you have to remember I started the website before I began my electrical engineering education in college. It needs to be updated. I know much more now.

Last edited: May 30, 2009
8. ### subtech Senior Member

Nov 21, 2006
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I have been teaching apprentice lineworkers and electricians for years and have found that water and compressed air analogies can be very confusing and can hinder the grasp of more advanced subjects later on.
I teach basic electricity starting at the level of the atom. Learning (with color coded pictures) about protons, neutrons, and electrons seems to me to work best. When students see that the electrons are actually moving from atom to atom, they can grasp "flow". This defines current graphically and gives it substance. I stress that all matter is composed of atoms and the electrons that move in any circuit are not provided by a battery or generator, but are always present in the conductors. Much effort is made to make sure that students understand that current flow is measured in units called amperes and that 1 ampere equals a very definite amount of electrons moving past a given point in one second.

Voltage is the unit that quantifies EMF. I strive to make sure that everyone in my class understands that electromotive force makes the electron moves from its orbit. Electromotive force is measured in units called Volts.

I teach that resistance to current flow is measured in units called ohms and is illustrated as the magnitude of attraction of unlike charges. The electron in its orbit around the nucleus has a negative charge, and the proton in in the nucleus of the atom which is positively charged.
No effort is spared in illustrating and explaining to the student why that in materials we consider conductors, electrons are much more easily made to move than in those of insulators.
Once students grasp these facts, ohms law (the mathematical statement of proportion of quantities) has lasting meaning.

Generally, troubleshooting a faulty electrical circuit involves finding the cause of one of two things.
The flow of too little or no current (circuit open),
Or, too much current (circuit shorted).

Some say that troubleshooting is an art.

Actually, if you don't know the science first, you can forget the art.........

Last edited: May 30, 2009

May 28, 2009
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I teach how components work by having the students build a simple breadboard circuit, then for example, see how a transistor amplifies by using an o-scope; Capacitors charge and discharge by watching a grain-of-wheat lamp dim and light; resistors by measuring voltage drops and current measurements; how transistors switch by a simple blinking LED circuit; how diodes rectify by using an oscilloscope; how tank circuits work by using a spectrum analyzer.
I know most people don't have access to test equipment, so they make due with what they have. Using any analogy that works is good, but there is no substitute for actual practical exercise. Plus, the student gets a confidence boost when the little circuit actually works!

10. ### studiot AAC Fanatic!

Nov 9, 2007
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Let us say you are taking a ride in the Eurostar train.

Would you really want to know that the servicing had been done by fitters with a good knowledge of hydraulics, but no knowledge of electricity other than that given in the OP's 5 day course?

11. ### count_volta Active Member

Feb 4, 2009
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The air and water analogies are really good for having kids or people first learning about electricity have something to compare electrons with, that is easier to understand and they are more familiar with, than particles so small that no one has ever seen them, and whose behavior can only be described by quantum mechanics and complex math.

Not everyone is mathematically inclined. These analogies are of course only good for the beginning of your learning. After you explain the basics, which I 100% agree should start with the atom (as you will see on my website in my previous post) then you can begin explaining more complicated things and use math.

I myself started out absolutely horrible in math, I became interested in electronics, and my interest pushed me to learn math, and now I am in advanced calculus courses and doing pretty good.

12. ### SullivanTrainingSystems Thread Starter New Member

May 26, 2009
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I appreciate all the responses - biting and otherwise. I'm a little taken aback at the extent to which my simple question was expounded upon, and the form that the replies took. Having taught electricity to technicians now for over 25 years, and having seen the ludicrous way in which electrical books parrot the ones that preceded them, I was hoping there might have been a response that was indicative of a desire by some to break free of the chains of convention in the curricula.

If we ignore the pretentious response, the others seem to stick to the traditional methods of teaching that depend upon history, instead of logic. Simpler is better. The balloon example also works well for resistance and flow; depending upon how the stem of a filled balloon is held, flow will change, based upon the resistance of the opening. Of course, many will now throw in the "changing pressure > changing flow" qualification, but those of us who work on big toys for big boys know that our voltage remains constant, so that trifling detail can be dismissed as irrelevant.

Either way, I believe that the overused and less-than-effective examples of our fathers and great-grandfathers are out of date, and deserve a good pouring over to see exactly how well they actually work. Those of you who teach on a theoretical level (and it appears there are many of you who do...) might fail to realize that on the operational level, we make field changes that completely replace the original systems. In many cases, the engineers are dependent upon us for guidance, and we typically generate solutions that are infinitely more reasonable than the learned ones.

Just because someone is exposed to and forced to endure an exhausting recitation of a 50-year-old lesson plan doesn't mean they appreciate it.

And by the way, having taught in Europe, 2 of my students are mechanics on the Eurostar. Hold on tight next trip...

Nov 9, 2007
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