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  #1  
Old 12-20-2007, 09:01 PM
Mr. Sharkey Mr. Sharkey is offline
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Default Disagreement on Wiki Entry

I have to take issue with the latest Wiki entry "Amps, Volts, etc." Using the "water analogy" should not use "speed of water" to explain volts, nor should current be associated with the "width" of the water flow.

Here's why I disagree:

1) The speed of electricity is for all purposes, constant. Comparing it with the velocity of water is misleading, and infers that electrons can and do travel slower than others (in practical terms).

2) When determining water delivery, the "speed of the water" is totally irrelevant to the equation. Municipal utilities don't figure system losses in terms of speed, they figure it in terms of pressure loss. The pressure of the water is what is used in the figuring of water delivery. If you're a fireman, you don't care how fast the water is travelling in the fire hose, you care about how much pressure it has at the nozzle. Also, the pressure drops in a closed water system when the flow (current) is increased. This has a direct relationship with voltage drop in an electrical circuit. Saying that the speed of the water is like voltage creates a situation where if the valve at the end of the pipe is closed, there is no velocity, so there is no pressure? Does the source voltage go away when the switch in a circuit is opened? Both situations are answered by comparing to pressure. You can have pressure in a shut-off garden hose, just as you have it in an open circuit.

3) It doesn't matter how "wide" the conductor is in either liquid or electrical circuit, at least in terms of calculating the amount of work accomplished, as long as the conductors/pipes are large enough to not introduce losses. A 4 foot diameter pipe can deliver as little as a gallon per minute, and a 1" pipe can deliver 100 gallons per minute (assuming enough pressure). Current would best be described as the flow, or amount of water passing though the pipe any given interval, ignoring the size of the vehicle that carried it there. Electrical current is defined as a measured number of electrons passing a fixed point in an interval of time, rather like saying that a well produces 5 gallons per minute.

Water: Pressure x flow = quantity (delivery)

Electricity: Amps x volts = watts (delivery)

At any rate, this is how I've heard the water/electricity analogy explained for the last 45 years or so. I'd suggest some research to dig up a reference source if you want to use the speed/width explanation, I think it's faulty.
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  #2  
Old 12-21-2007, 05:48 AM
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mattW mattW is offline
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Default Re: Disagreement on Wiki Entry

I'm inclined to agree, sorry Robert. Using Pressure and rate of flow is a little bit more useful as an analogy but Mr Sharkey I suggest you go ahead and edit the article yourself (though it was a good policy to ask first). That is what the wiki is for; so we can hone and polish each other's ideas. Just Click 'Advanced Edit' at the bottom of the article and its just like editing a forum post. Cheers
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Old 12-23-2007, 12:14 AM
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Default Re: Disagreement on Wiki Entry

That is the whole point of the wiki! Thanks for being democratic. I take no offense to any changes and I highly encourage a correction if it's needed!
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Old 05-16-2008, 11:57 AM
Wirecutter Wirecutter is offline
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Default Re: Disagreement on Wiki Entry

At one point, I thought I'd actually invented the water-electricity analogy. I know, I didn't - but I did come up with it independently. Others simply did it first.

I also disagree with the wiki entry, once I found it. I think I mostly agree with Sharkey, but maybe say it a little differently. Volts are not analogous with water speed, they're analogous with the pressure. Amps are defined as the number of electrons moving past a given point. That's your speed (or flow) analogy.

So more voltage (pressure) can facilitate more amperage (speed). More voltage (pressure) also means you can move more watts (gallons per minute) through the wire (pipe). Watts are analogous to "gallons per minute" or some other quantity of water per unit time. Kilowatt hours similarly relate to the amount of water delivered.

The analogy has to get creative to explain magnetism, but you can still use it to explain resistance, inductive reactance, and capacitive reactance. But all that's for the more advanced course. I always though of the electricity-water analogy as a way to explain it to non-electrical types.

My $0.02

-Mark
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Old 05-16-2008, 11:59 AM
Wirecutter Wirecutter is offline
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Default Re: Disagreement on Wiki Entry

Pardon my ignorance and late entry to this thread, but can just anyone edit the wiki? I'll step up and do it if nobody else wants to..

-Mark

-edit - never mind, I found my answer. I'll edit it, and check back to see if we all agree.

Last edited by Wirecutter; 05-16-2008 at 12:02 PM.
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  #6  
Old 05-16-2008, 12:23 PM
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Default Re: Disagreement on Wiki Entry

Yes, it's a wiki. It seems everyone is in agreement that the water analogy needs to be reworded a bit. Feel free to fix it!
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Old 05-22-2008, 11:19 AM
ngrimm ngrimm is offline
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Default Re: Disagreement on Wiki Entry

I understand the water analogy except for one thing. Would 50% DOD mean the container is half full or half empty? Norm
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Old 05-22-2008, 12:28 PM
Wirecutter Wirecutter is offline
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Default Re: Disagreement on Wiki Entry

Quote:
Originally Posted by ngrimm View Post
I understand the water analogy except for one thing. Would 50% DOD mean the container is half full or half empty? Norm
I'll probably figure it out a few seconds after I post this, but what's "DOD"?

-Mark
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Old 05-23-2008, 11:26 AM
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Default Re: Disagreement on Wiki Entry

Find DOD in Glossary of Abbreviations
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  #10  
Old 05-23-2008, 02:12 PM
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Default Re: Disagreement on Wiki Entry

Quote:
I understand the water analogy except for one thing. Would 50% DOD mean the container is half full or half empty? Norm
It means you've got too much grease and dirt clogging the walls of your pipes.

I agree with the Pressure = Voltage analogy it is a very good one.
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