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I understand that this is a really basic question, but, I've been unable to really understand electrical terminology for some reason. What exactly is an amp? How does it correspond to a watt?

And: How does a watt correspond to a volt? What does the frequency of electricity refer to? (Hz, 50/60)

Please be as specific, and laymeny as possible :).

Thank you!

Edit: Since I didn't get anyone yelling at me for talking about adding a few more questions, here goes:

What is a volt? My understanding of it is the difference between the neutral and phase, but, this doesn't make it any clearer. If anyone can help out with more information, with an analogy or two, plus some technical information, I'd appreciate it very much!

What does the "earth"/ground portion of the circuit do? How does it help safety? If it helps safety, why aren't all plugs 3-pin instead of 2-pin?

Hypothetical:

If I plugged in two wires to a socket, and put the other end into something conductive (for instance, a bucket of water), assuming the breaker doesn't go off (if it would, why would it?) after I remove said wires(or turn off the socket), does the water "hold" the charge? Is it in any way unsafe?

For what it's worth, I'm assuming no. The current flows from phase-neutral, the water simply facilitates this. Right? If I'm right, I assume this means that I am in some way "using" the electricity? How does this differ if I for instance put the wires up against a block of wood? How does it differ if I stick the wires on myself?

I apologize if some of these questions show a fundamental mis-understanding of electricity. If they do, smack me across the head and point me to a resource that will educate me and help me answer such questions myself. These questions have plagued the back of my mind for a while, but I've never found the right place to ask.

I have more such questions, both hypothetical, and real (how does a stabilizer work, why is it required? Why do motors require 2x as much electricity to start up vs to run? Why can't this be optimized/why hasn't it been fixed yet?). I'm hoping I'll be able to answer the hypothetical ones myself once I gain more of an understanding, with your help.

I hope questions at these level (and their answers) are useful to at least one other person!

Again, Thanks to whoever helps me out!

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Is it acceptable practice to add more questions on to an answered question? I have more basic questions, and, seeing as how quickly and succinctly this one was answered, I'd love to ask more, just wondering if I have to open a new question for those, or fit them in here under the theme of "basic" questions as stated by the title. –  Jon Binder Nov 6 '10 at 7:47
    
your follow-on questions seem to be aimed at the concept of resistance. The ratio of the current you get, for the voltage you apply, is the item's resistance, usually specified in ohms. "Ohm's Law", V=IR, is just the algebraic expression of this. –  JustJeff Nov 6 '10 at 13:24
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It might be more effective to break your questions up into separate postings, as it will help organize focused answers in a way that makes the material more accessible to future users. But that's just my 2 cents. –  JustJeff Nov 6 '10 at 13:27
    
I think justJeff is correct. We will still answer questions quickly. –  Kortuk Nov 6 '10 at 13:32
    
I'm an ex-EE doing software. I found this old book as a toss away which is excellant for getting started amazon.com/gp/product/B0007K6908 –  kenny Feb 15 '12 at 15:24

5 Answers 5

up vote 12 down vote accepted

An ampere is a measure of how many electrons move past a point every second (though technically, it's movement of any charged particles, but for metal wires it's always electrons). 1 ampere = 6,241,510,000,000,000,000 electrons per second. A pipe with water moving through it could be measured in gallons per second. Same idea.

Watts are not just used in electronics. They're a measure of the rate at which energy is used or transferred. A firecracker uses up chemical energy faster than a candle, even if the total energy is the same for both, so the firecracker has a higher power output for a shorter time. Likewise you could use two identical batteries in different ways. If one way uses more power, the battery will not last as long.

1 horsepower is about 750 watts, if you're familiar with cars. Just different ways to measure the same thing.

watts = volts * amps. So a 60 W bulb plugged into a 120 V socket will be drawing 1/2 an amp.

60 W = 120 V * 0.5 A

In AC circuits, the electrons are vibrating back and forth instead of going in a continuous loop. The frequency is just the number of vibrations per second. 50 Hz means they move back and forth 50 times per second.

It's important to understand the difference between current flow and energy flow, though. The actual electrons in a wire don't move very fast. In a DC circuit, the actual electron flow around the loop might be at the speed of molasses. The reason flipping a switch causes the light to turn on very quickly is because the energy flow is very fast. The energy is carried by waves in the electrons, not the electrons themselves. They are constantly repelling each other, so when you push some extra electrons onto one end of a wire, the others nearby jump away, which causes more near them to jump away, and so on, creating a wave of "push" that travels down the wire and then pushes on things at the other end. This wave travels from one end of the wire to the other at maybe 2/3 the speed of light, while the electrons themselves barely move.

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Just to make sure I'm correct: Amps = Watts/Volts. So, for a fixed voltage (for example, 120V), a computer which uses 400 Watts will "use"(is this the right terminology, it seems wrong, but I can't think of anything better?) 400/120 = 3.33 amps? Thank you, your answer was pretty much perfect! –  Jon Binder Nov 6 '10 at 7:40
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@Jon Binder - sometimes people say 'draw' or 'pull' for current, but 'uses' is just fine, too. –  JustJeff Nov 6 '10 at 13:18

You'll find an excellent and clear explanation of the physics behind electricity in the article: How are Watts, Ohms, Amps and Volts related?

He doesn't explain it like convertional textbooks. He is a physicist, not a mathematician, and explains it as such. When I was learning, that small article cleared up a lot of confusion I had and I refer back to it frequently for a refresher on the basics.

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I understand the relations better now, as well as what an amp is thanks to endolith, but still fail to understand in any "real" tangible way what a volt is (in the electrical sense, that is, not just as a converted unit for instance, with amps to HP). In addition, I would still love some answers (or a smack) for the hypothetical questions (as idiotic as they might be to others). Thank you for the link, nonetheless. –  Jon Binder Nov 6 '10 at 10:17
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+rep for the link. After so many years, finally something that helps me understand these concepts better. –  luis.espinal Nov 6 '10 at 14:16
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I've found it useful to think of voltage as pressure. –  pingswept Nov 6 '10 at 20:39

Endolith explained the current very succinctly.

Volage is a measure of how much potential energy the current has. You are probably used to potential energy from other subjects. mgh is a common equation for potential energy when you have a gravitational field and you raise a mass into the air. when you let the mass go it will have an amount of potential relational to its height and its mass.

If you have water, the higher you pump it into the air the more potential energy the water will have. If you then bring the pipe all the way back down to the bottom where there is a turbine that resists the flow of current(current of water) then it will do work on that turbine. The turbine will receive power relative to the amount of water that is moving(the current) and the height the water was(its potential).

I hope that helps.

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Here's another example of a water analogy applied to electricty: hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html –  tcrosley Nov 6 '10 at 16:02

The basic analogy that tends to work for most people is plumbing/water pressure and flow.

The first analogy is water pressure == voltage. Imagine if you will a water tower - a big tank full of water high off the ground that has an outlet pipe going to ground level with the flow controlled by a valve. Gravity acts on the water causing it to exert pressure on the valve when it's closed. The pressure on the valve varies with the amount of water in the tower, the air pressure around the water and the size of the valve.

The water tower is similar to a battery (but not exactly the same). The battery stores electrical charge instead of water and the pressure is caused by the density of the charge - essentially the electrical charge wants to get away from other like charges. The voltage of a battery is analogous to the pressure of a water tower. The pressure/voltage is a measure of the ability of the water/charge to do work.

So pressure is equivalent to voltage - a battery has a voltage just sitting there even if all of the charges aren't moving or doing any work in the same way a water tower has pressure just sitting there with no water moving. When water does start to move, this is equivalent to current.

Electrical current is simply electrical charges moving (charge per second), water current is simply water moving (unit volume of water per second). Bigger pipes let more water flow and release more pressure, so the pressure at the end of a pipe is less than the pressure at the beginning. Similarly, for electricity, 'bigger pipes' means lower resistance. Low resistance means lower voltage at one end of an electrical 'pipe' (maybe a resistor or just a wire) than at the other end. In the real world, water flows from a high pressure/potential place (the top of the water tower) to a low potential place, ie, the ground. Just the same for electricity - one end of a battery is high potential, high voltage and the other end is low potential/ground.

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How about ampers? where does it belong? I usually see batteries with different amperes but just ame volts. how can it affect the load? –  Pennf0lio Feb 15 '12 at 15:52
    
btw, I really appreciate how you explained it. thank you. it really put some light on my question. –  Pennf0lio Feb 15 '12 at 15:53
    
@Pennf0lio Amps is how fast the water is moving. An amp rating on a power supply is the how fast the water is able to move (but not necessarily how fast it is actually moving). Then the Amp hour capacity on a battery is sort of how fast the water can move for a given period of time. –  Kellenjb Feb 15 '12 at 15:58
    
I think amp-hours are better stated as a measure of capacity - ie, how much water the battery can hold... you get the idea ;) –  AngryEE Feb 17 '12 at 14:57

A great resource for self learning the principles of electronics across a broad range of topics is the Navy Electricity and Electronics Training Series, popularly known as NEETS. Publicly available, the 24 module set can be downloaded from here: http://jricher.com/NEETS/

Another solid resource is the Amateur Radio Relay League's Handbook: http://www.arrl.org/arrl-handbook-2012. The handbook is geared more towards radio communications.

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