Difference between voltage/current?

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Old 06-20-05, 01:16 PM
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Difference between voltage/current?

Hello guys, could you please explain (in Layman's terms) the difference between voltage and current, and why each is important in their own rights? Thanks!
 
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Old 06-20-05, 01:58 PM
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This is a very general way to think of it...Think of it in plumbing terms.
Pressure = voltage, and volume = current. Example- a small pipe with a large pressure would be like a higher voltage with a low current flow, and so on...
You get the idea
Again, this is very simplified.
 
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Old 06-20-05, 02:37 PM
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Originally Posted by Andrew
This is a very general way to think of it...Think of it in plumbing terms.
Pressure = voltage, and volume = current. Example- a small pipe with a large pressure would be like a higher voltage with a low current flow, and so on...
You get the idea
Again, this is very simplified.

That's a good analogy. Also it helps to remember one of the basic equations you learn in Electrical 101 class: Power = potential x current (watts = volts x amps)

A very simplified way of looking at it is the more power you suck up from the electric company, the higher your electric bill is

But I'm sure that was probably pretty self-explanatory huh?
 
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Old 06-20-05, 03:10 PM
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Here's another thought. Most light bulbs in your house use exactly the same voltage (120 volts), but they use different amount of current. A 60-watt bulb draws one half of an amp of current, and a 100-watt bulb draws almost an amp. But the both run on 120 volts. You pay for energy (watts consumed over time), not volts, not amps, and not watts.
 
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Old 06-20-05, 09:39 PM
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Think of this: The your kitchen faucet has about 60 pounds of pressure sittinjg there. However, there is no way for the water to flow. Now, open the faucet and the water has someplace to go. Just how much flows is determined by how much the pressure was and how much you open the valve.


The plug in your wall has 120 volts of electromotive force sitting there. No current flows because there is no place for it to go. Plug something in and the amps start flowing. Just how many amps flow is determined by the force , in this case 120 volts, and by the RESISTANCE of what you plug in. A 100 watt bulb has a lower resistance than a 60 watt, so MORE current will flow.
 
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Old 06-27-05, 11:30 AM
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Thanks guy for the awesome answers. How does one measure voltage? Does voltage have anything to do with the wave pattern of the electricity, or is that strickly a function of hertz. If you could see electricity, would more volts make the energy flow any faster? I suppose the question is: how can you tangibly describe volts? I understand how it plays a role in the equation, but tangibly what does it mean? I suppose a roundabout way to answer that question is to explain how voltage can be raised and lowered by the power company. How is the power company able to adjust voltage supplied to their customer? I'm sure they have some special dial, but how does that dial affect the electricity's voltage? Thanks guys!
 
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Old 06-27-05, 12:00 PM
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Electricity travels at the speed of light. It was once said of a baseball player particularly adept at stealing bases (Lou Brock?) that he was so fast that he could flip the switch on his bedroom light and be in bed before the light went out.

A.C. voltage is "adjusted" by transformers, regulators and load tap changers. Regulators and load tap changers are variations of a transformer. Whereas a transformer has a definite turns ratio (some have some provision for slight adjustments with various taps), a regulator or load tap changer is used to change the turns ratio under load. Some voltage regulation is accomplished by boosters (again, just another variation of a transformer). In a completely different way, some voltage regulation is accomplished with capacitors. In my area, the voltage at the output of the generator at the power plant is anywhere from 12,000 to 22,000 volts. It is immediated stepped up to at least 138,000 volts. There may be some "generator mains" that step it up higher, but I've been away from that a long time. In the switchyard, the voltage is often stepped up to 345,000 volts (phase to phase) for long distance transmission. Common transmission voltages in my area are 69 KV, 138 KV and 345 KV. Distribution substations then step it down to either 12,470 V, 13,200 V (Dallas only) and 24,940 V for distribution to homes and businesses. Then, a variety of sizes and voltages of transformers are used to step the voltage down for final consumer use. Most residential applications are 120/240 volt single phase, but commercial and industrial can be many other voltages. They start out at 120/240 volt, 4 wire, 3 phase as this can be derived from only two primary phases and two single phase transformers. Other common voltages are 120/208Y, 277/480Y and 480 delta. Industrial customers also have 2400/4160Y, 2400 delta and sometimes even take one of the un-transformed distribution voltages (12,470, 13,200 or 24,940). Some even take 138,000 (such as a plant near Midlothian, Texas that melts down scrap automobiles into rebar and other steel products using an electric arc furnace.
 
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Old 06-27-05, 12:14 PM
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Both current and voltage would look like a sine wave if viewed on an oscilliscope. Both are 60 hertz (although not necessarily exactly in phase with each other).

The reason voltages are stepped up during transmission is to reduce current, and thus save resistance losses in the line. The reason that they are stepped down before it gets to your home is safety for you.

The power grid is all alternating current (AC) and also alternating voltage of course, because AC voltage is much easier to step up and down than direct current (DC) is. This is the source of the famous Westinghouse/Edison debate of a century ago. As you know, AC (Westinghouse) won the battle over DC (Edison) because of its ability to be easily voltage stepped.

would more volts make the energy flow any faster?
The rate of energy flow is called "power" and is measured in watts. Power is a function of both voltage and current. If you use a transformer to step up the voltage, the current will drop by a corresponding amount. So the power is the same. So the answer to your question is generally "no" if you're talking about power distribution. But looked at another way, the answer could be "yes". A given light bulb will use more power (i.e., energy will flow faster) if you give it more voltage (because it will also use more current).

BTW, electricity traveling through copper wires travels considerably more slowly than the speed of light.
 
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Old 06-27-05, 01:12 PM
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I guess you're right. Due to the resistance of copper, electricity travels at only 299,792,458 meters per second, whereas light travels at 300,000,000 meters per second in a vacuum.

207,542 meters per second is considerable, so that electricity travels at only 99.93% the speed of light. Still pretty fast!
 
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Old 06-27-05, 01:16 PM
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Are these test questions for school ?
---------------------
" How does one measure voltage? " With a volt meter.
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" How is the power company able to adjust voltage supplied to their customer? I'm sure they have some special dial, but how does that dial affect the electricity's voltage? "

They regulate the magnetic field in the generator.
 
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Old 06-27-05, 10:58 PM
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This analogy probabliy isn't correct. But, I like to think of voltage as how far the little electron can jump. The higher the voltage means potential to jump further distances. And amperage or current is how many electrons are jumping.
 
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Old 06-28-05, 06:43 AM
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Phil, no analogies are exactly correct, but I like yours.
 
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Old 06-28-05, 10:20 AM
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Originally Posted by Phil H
This analogy probabliy isn't correct. But, I like to think of voltage as how far the little electron can jump. The higher the voltage means potential to jump further distances. And amperage or current is how many electrons are jumping.
Not exactly. The electrons are not actually moving at the speed of light, it is the electrical field that moves at or near the speed of light.

The actual electron flow is extremely slow, so slow in fact, that if you could see it, it would probably lull you to sleep. Also, it is always against the direction of current, so in an AC system, they would actually be changing direction.
 
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