Amps vs Volts vs Watts

[Smoblikat]

Hey everyone, had a random thought pop into my head just now. I dont fully understand the difference between A, V and W. From what I was told a long time ago:

Amps are like the "Pressure" the current is flowing at.
Volts are the type of current that is flowing.
Watts are the total amount of current being produced.

How accurate are these statements? Also, from what ive heard, volts dont really kill you (unless its an extremely high voltage) but even just 1 amp could kill you. Is that true also?

 

[silicon]

a Watt quantifies the power being dissipated. W = E x I.
An ampere is the amount of electrical current flowing in a circuit.
a volt is the electrical pressure in the circuit.

 

[rgallant]

AMP's -more like water flow in a garden hose

you have water coming out of the tap @ xx pressure [volts]
a 1" hose will let water [amps] flow/fill faster than a 1/2" hose into a bucket [watts/power]
more water flow[volume] = more power

a 1" hose is less restrictive than a 1/2" hose at the same water pressure.
-but if a 1" hose at 40psi would have the same water flow [amps]as the 1/2 hose at 80 psi
-turn the tap on more [higher volts] you get more water to flow so more power.
http://electricalengineeringforbeginners.blogspot.ca/2009/08/basic-concept-of-ohms-law.html

Also, from what ive heard, volts dont really kill you

my take on that is you can't have current with out volts
-grab a black conductor from a wall plug [120 volts] with one hand could be a small or big bite depending on your body Resistance to ground of the house,

now grab the same conductor with one hand then grab a copper/grounded pipe with the other hand, doing that will lower your resistance to the ground path and will likely kill you as the current flows though your heart.

 

[inachu]

If you never got your finger stuck in the wall socket then you will not truly what the differences are but you can feel the difference.

No I am not telling anyone to do anything that dangerous but because of accidental shocks myself while taking electrical engineering as a teen I can tell you it really was a learning experience.

 

[Hitman928]

Hey everyone, had a random thought pop into my head just now. I dont fully understand the difference between A, V and W. From what I was told a long time ago:

Amps are like the "Pressure" the current is flowing at.
Volts are the type of current that is flowing.
Watts are the total amount of current being produced.

How accurate are these statements? Also, from what ive heard, volts dont really kill you (unless its an extremely high voltage) but even just 1 amp could kill you. Is that true also?

Not that great of descriptions. What's your science/physics background. Do you know the difference between potential and kinetic energy? Water comparisons to electricity are kind of like car analogies for computers, can be good for very basic understanding of concepts but usually horribly over analyzed and misused.

 

[FrankSchwab]

Water comparisons to electricity are kind of like car analogies for computers, can be good for very basic understanding of concepts but usually horribly over analyzed and misused.

Yeah, yeah, yeah, but for the OP's level of understanding, they work just fine.

Analogy: Electricity in a circuit is like water in a garden hose.

Voltage is like the water pressure in the hose. You can have Voltage (Water Pressure) with nothing happening - for example, an open electrical circuit, or a hose with a closed end. The potential is there to cause excitement if something changes (the circuit closes, or a hole opens in the hose).

Amperage is like the amount of water flowing through the hose. Electrically, it's a measure of the number of electrons flowing in the circuit, where for the hose it'd be similar to counting the number of water molecules flowing out of the hose.

The amount of water flowing through a hose is correlated with the amount of pressure at the hose bib pushing water through the hose - higher pressure causes a higher flow. Similarly, the amount of current you can get through a simple circuit is correlated with the voltage driving the circuit - higher voltage, higher current.

Watts is simply the product of Current times Voltage. It's a measure of the amount of power flowing through a circuit - a 10 amp current flow driven by a 1 Volt potential is exactly the same amount of power in Watts as a 1 amp current flow driven by a 10 volt potential. It would take two different circuits to create these two situations, of course.

In the water analogy, imagine a water wheel (http://en.wikipedia.org/wiki/Water_wheel). If you shot a high pressure water stream (high voltage) at the wheel out of a small hose (low current), you can imagine a situation where it spins at the same speed (generates the same power) as if you shot a low pressure (low voltage) stream of water out of a big hose (high current).

You can buy a 60 Watt light bulb that operates at 120 volts, or a 60 watt light bulb that operates at 12 volts. The first would have Amps=Watts/Volts=60/120= 0.5 amps flowing through it, while the second would have Amps=60/12= 5.0 amps flowing through it, but if you were generating the power by sitting on a bicycle equipped with a generator, you'd have to work just as hard to light both. Woe is you if you hook the 12V light up to the 120V generator, though (the 12V light has a lower resistance, so more current would flow - momentarily, the light would dissipate 600 watts, just before the filament melted spectacularly) (But you didn't ask about resistance).

Hope this helps..

 

[silicon]

And don't forget that in circuits you have conventional flow vs electron flow. Our understanding is that current flow from positive to negative but in electron flow the surplus electrons at the negative move to the positive. Its a bit confusing since both are used.

 

[Murloc]

Hey everyone, had a random thought pop into my head just now. I dont fully understand the difference between A, V and W. From what I was told a long time ago:

Amps are like the "Pressure" the current is flowing at.
Volts are the type of current that is flowing.
Watts are the total amount of current being produced.

How accurate are these statements? Also, from what ive heard, volts dont really kill you (unless its an extremely high voltage) but even just 1 amp could kill you. Is that true also?

not a good vision.

The charge is a quantity of water.

Current (amps) is the volume flow rate of water, the liters per second.

Volts is the pressure, or if we're talking about gravity, being at a higher voltage is equal to being higher.
Charge at high voltage will discharge to ground, water in the sky will fall too.

Watts are power, energy per second.

The wiki page is not too shabby: https://en.wikipedia.org/wiki/Hydraulic_analogy
This website is pretty good: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir2.html

 

[razel]

I really wanted to chime in to correct Smobilikat's analogy, but Murloc's got it. Again to simply in the OP terms of the water analogy:

Amps = flow amount of water (per interval)
Volts = water pressure

Watts = Amps x Volts

If you want to take it further... Wire gauge = pipe diameter. That water analogy seems pretty popular in the car audio world. There are very good videos by D'Amore Engineering at youtube as a very good start.

 

[unokitty]

V=IR

Power in watts P=VI

Uno

 

[silicon]

V=IR

Power in watts P=VI

Uno

electron theory has the arrow's pointing in the other direction

 

[Mark R]

electron theory has the arrow's pointing in the other direction

Electric current is always drawn as flowing from positive to negative.

This could mean positive current carriers flowing from positive to negative, or negative current carriers flowing from negative to positive. This avoids confusing problems with negative signs, etc.

Yes, it is more common in bulk electrical transport for electrical current to be carried by negative carriers (electrons), but this is not always the case.

 

[IHateMyJob2004]

Volts are like psi in a water lone.

Amps are the volume of water through the line.

 

[silicon]

Electric current is always drawn as flowing from positive to negative.

This could mean positive current carriers flowing from positive to negative, or negative current carriers flowing from negative to positive. This avoids confusing problems with negative signs, etc.

Yes, it is more common in bulk electrical transport for electrical current to be carried by negative carriers (electrons), but this is not always the case.

you may be incorrect in your assertion....

In conventional flow notation, we show the motion of charge according to the (technically incorrect) labels of + and -. This way the labels make sense, but the direction of charge flow is incorrect. In electron flow notation, we follow the actual motion of electrons in the circuit, but the + and - labels seem backward. Does it matter, really, how we designate charge flow in a circuit? Not really, so long as we're consistent in the use of our symbols. You may follow an imagined direction of current (conventional flow) or the actual (electron flow) with equal success insofar as circuit analysis is concerned. Concepts of voltage, current, resistance, continuity, and even mathematical treatments such as Ohm's Law (chapter 2) and Kirchhoff's Laws (chapter 6) remain just as valid with either style of notation.
You will find conventional flow notation followed by most electrical engineers, and illustrated in most engineering textbooks. Electron flow is most often seen in introductory textbooks (this one included) and in the writings of professional scientists, especially solid-state physicists who are concerned with the actual motion of electrons in substances. These preferences are cultural, in the sense that certain groups of people have found it advantageous to envision electric current motion in certain ways. Being that most analyses of electric circuits do not depend on a technically accurate depiction of charge flow, the choice between conventional flow notation and electron flow notation is arbitrary . . . almost.

 

[dave_the_nerd]

In high school it was explained in the context of a stove burner.

Voltage is how hot the burner is set. Could be room temperature, could be a thousand degrees.

Amperage is how LONG you hold your hand on the burner. You can hold your hand on a room temperature burner all day (low voltage, high amperage). You can slap your hand against a very hot burner for a very brief period of time and not get hurt (high voltage, low amperage.) In the middle, given enough time (amperage), a 150 degree burner (might not feel super painful at first) can do some damage to you.

Wattage is the "work done." In this analogy, it's how badly you are burned.

 

[DrPizza]

I'll take a shot at explaining this to Smoblikat

Even before Ben Franklin, plenty of people were playing the electrical phenomena. Yet, the electron wasn't discovered until 1897. So, while we might think of the unit of charge as being an electron, it's actually the Coulomb, which is a crap load of electrons. It would be like purchasing a baking ingredient called eggs, but the base unit was a dozen, and it wasn't discovered for another century that there were 12 things inside of it.

Now, as an analogy, I'm going to use water. And, one unit of water is going to be a kilogram of water. If you lift water from height A to height B, it takes some work to move it up. And, it gains some potential energy - it now has the ability to do a certain amount of work (turn a water wheel, for instance). So, we could say that there's a certain amount of energy available per kilogram of water. Energy is measured in joules. From point A to point B, you have n amount of joules per kilogram of water.

Now instead, let's do this with things that have charge. If you've ever played with things that are charged, you might notice that sometimes they're attracted to each other, and sometimes repelled from each other. It's similar to how opposite poles of magnets attract each other, and like poles of a magnet repel each other. Let's assume we have to charged balls, one positive, and one negative. They're attracted to each other. We'll pick a point A near the positive ball, and a point B farther away from the positive ball. We're going to push the negative ball from point A to point B. That takes some work. And, when we push them apart, they want to fly back toward one another again. So, they've gained some "potential energy" from point A to point B. Or, we could call it a potential difference. From point B, to point A, there's a certain amount of energy available to do work for us. And, the greater the charges, the stronger their attraction to one another. So, we'll measure the amount of energy available per unit of charge, or the joules per coulomb. This is very similar to the joules per kilogram of water in the analogy. Oh, and there's a shorter name for joules per coulomb: volts. Potential difference as I referred to it is often called voltage.

Let's go back to the water analogy. When water flows, we call it current. In the upper Niagara River, so many kilograms of water flow past a point per second. Thus, we could measure current as kilograms per second. (Of course, with water, we can use other units - gallons of water per second, cubic feet per second, etc., but these could, if necessary, be converted to kg/second.) And, in the upper Niagara, those kilograms of water have the potential to do some work for you, because they're raised above point A by the height of Niagara Falls. So, as those kilograms of water flow toward the Falls, we know there there is so many joules of energy per kilogram associated with them. If 1 million kilograms were flowing over the falls per second, and each kilogram was able to do 4 joules of work turning that water wheel, then we'd have 4 million joules of energy per second from those kilograms of water going over the Falls.

Likewise, in your electrical circuit, you have so many coulombs of electrons flowing past a wire per second. This is also called current, measured in coulombs per second. The shortened name for coulombs per second is amperes, or amps for short. And, each of those coulombs has an amount of energy associated with it - so many joules per coulomb (volts) as I described above. Instead of a waterwheel at the base of a falls, those electrons are pushed through a light bulb. Let's say 4 amps, that is, 4 coulombs per second is the current, and the energy per coulomb (voltage) is 20 joules per coulomb, then each second, there are 80 joules of energy making light and heat for you. 80 joules per second is a unit of power, and is commonly called a watt.

Parallel circuits - at Niagara Falls, the river forks. Some goes over the Canadian side, some goes over the American side. Thus, the current is split up. But it falls the same distance. Thus, voltage (joules per coulomb) is the same on each side, but the current is split in two until after the two branches come together in the Niagara gorge.

Series circuits - this would be like a series of waterfalls - drop 50 feet, then 30 feet, then 20 feet. One stream that doesn't split up. The current is the same at each drop (as long as no other streams merge in.) The potential difference (joules per kilogram of water) between the highest point of elevation and the lowest point of elevation is broken up in that series of drops. Thus, it drops a certain amount of energy per kilogram over the first falls, then another amount of energy per kilogram over the second falls, and then another amount of energy per kilogram over the third falls. This would be the same amount of energy had there only been one taller falls. Ditto for electrical series circuit. So many volts (joules per coulomb) over the first "falls" etc. (Oh, and one possible point of confusion - I neglected to make the water turn a water wheel every time. So, instead of doing work like grinding your flour, you might think the energy per kilogram magically vanishes. What it actually does is heats up the water when it impacts the water below, though the measured temperature may actually be lower at the base of the falls due to evaporation as it falls.)

I've neglected to discuss electrical fields, since you didn't ask; but hopefully this gives you at least a beginning understanding. Others, feel free to critique; as this is similar to how I introduce it to students. (Though, I haven't proof-read the above; I was enjoying my dinner as I typed.)

 

[IHateMyJob2004]

In high school it was explained in the context of a stove burner.

Voltage is how hot the burner is set. Could be room temperature, could be a thousand degrees.

Amperage is how LONG you hold your hand on the burner. You can hold your hand on a room temperature burner all day (low voltage, high amperage). You can slap your hand against a very hot burner for a very brief period of time and not get hurt (high voltage, low amperage.) In the middle, given enough time (amperage), a 150 degree burner (might not feel super painful at first) can do some damage to you.

Wattage is the "work done." In this analogy, it's how badly you are burned.

That analogy makes no sense.

Electrons through a wire are like water through pipe.

 

[FrankSchwab]

OK, everyone's over the edge. Let's have some fun.

Electricity is like pissing.

Voltage corresponds to how full your bladder is.

Current corresponds to how much you're pissing. If you don't really have to go (the voltage is low), the stream is weak (the current is low). If you DO need to go (the pressure is high), the stream is strong (the current is high).

Does that help?

 

[DrPizza]

OK, everyone's over the edge. Let's have some fun.

Electricity is like pissing.

Voltage corresponds to how full your bladder is.

Current corresponds to how much you're pissing. If you don't really have to go (the voltage is low), the stream is weak (the current is low). If you DO need to go (the pressure is high), the stream is strong (the current is high).

Does that help?

My van de graaff generator can easily hit 100,000 volts. But, there's very little current. Prostate problems?

 

[Sho'Nuff]

My van de graaff generator can easily hit 100,000 volts. But, there's very little current. Prostate problems?

More like a kidney stone.

 

[FrankSchwab]

My van de graaff generator can easily hit 100,000 volts. But, there's very little current. Prostate problems?

No, that means that you drank a Super Big Gulp, are now stuck in a traffic jam with 10,000 of your fellow human beings and no bushes, and despite your best efforts you're leaking slightly.

Just don't have anyone in the car make you laugh. That corresponds to a big old zap from the van de graaf.

 

[philipma1957]

ON a good day after some steady beer drinking I can fill close to a half gallon bucket. How many watts would that be?

Would the beer be the positive electrons and the urine the negative ones.

As we all know beer flows that way? Towards the bucket of p-ss.

 

[AchillesT]

Hey bud,
Some really colorful metaphors given, probably the most important take away unless you're held accountable for such measurements...

That said, and without beating it with derivations and some *basic/repulsive* (who you're asking) physics - here's a straight forwardish attempt at clarifying a relationship common people rarely can tell apart, or remotely care in all fairness.

So, the one with maybe the least ambiguity given the question, Voltage. As said, analogized, this metric is about the difference in electrical potential between two points (crucial) so that a current of one ampere traversing the plane ("imaginary force field" in between those points) expends 1 Watt(*will return to*) of power in the process = 1 Volt. Alternatively, a Volt can be defined as one joule/coulomb, as well as other equal definitions probably not beneficial in clarifying. Also, the units i used will come full circle in a second...

Now, a watt. Defined as a particle(object) held at a constant velocity of 1-meter/1-sec opposed by a force equal to one newton, resulting in the rate of work done = 1 watt. So, 1-watt=(1-Newton*1-Meter)/1-second <=> 1-watt=1-joule/1-second. Think of this as how "expensive" in terms of how much work an element, or object is to operate, as well as a way of setting a maximum before an object is "overworked" (or minimum). In circuits, or considering watt unit electrical measurements, if a lightbulb is given as a 50-watt rating - then when in a closed circuit it will be absorbing (taking work) from the source at 50-watt, where as the source will be (lets say its a one bulb circuit) providing (--50 watts) (perfect world).....where the sign identifies an element as receiving or supplying (+ receiving, -- supplying).

I've tried using as few of units not to belittle anyone, but just to bring the seemingly "evasive" definitions into the whole later on hoping to best clarify the difference between them. The remaining measurement, Ampere is a factor in electrical circuits concerning watts - as watts don't act alone in the whole picture, but more as a "demand." Leading us to the definition of 1-Ampere being approx. equal to getting a "bunch of electron charges" to pass a point in a circuit PER 1-second. More accurately, 1-Ampere=6.214x10^(18) electron charge carriers (electrons)/1-second. <=> 1-Ampere=1-Coulomb/1-second. This "bunch" or stupid-big number (if one electron were 1 penny, a coulomb would be $62.4 QUADRILLION dollars!!! yikes) might help answer your second question, how accurate are these.....

Well, I think you could imagine we're dealing with a huge quantity of ridiculously small electrons, each weighing ~9.1x10^-31 kilograms (which means nothing to me too - so if the "size" of that number, |9.1x10^31| were inches - it would be more than 2000x the diameter of what we consider the universe!!!!)

So to conclude with the hazards, and although we're "departing" my area as I'm no doctor, or really all too familiar with biology etc., I'll try sticking to the electricity involved. First, whether we're using AC or DC plays a huge role, point of contact, general cardio health, or even how sweaty a person happens to be, are also significant variables in the shock & death - using a rough values(DC) we can say as little as 500mA (dont let 500 fool you ...) or 0.5A can cause fibrillation and death. Now, disredgard any folklore like "the voltage doesn't get ya, its the amps!" yada yada....Remember, V=Amps * Resistance or more simply - they are both in the mix! SO think of it in terms of Watts which is P=v^2/r <=> P=Volt * Amp so if we only had 1/2 an Amp at 120V we'd be looking at a power rating in one second of 60 W - with 110W being a rough daily expended by an adult male. Also the same as 60V @ 2 Amps, or 30V @4 amps or a little more than the shock received from 200V with human resistance of ~ 2100Ohms....with people being "resurrected" using about 5V/cm (defib)....

I hope I clarified a pretty roundabout relationship....it's a lot of different quantities and actions that form as an equality (why it''s better to think, "It's the Electrons that'll kill ya") and i'd avoid thinking of it like the simile because if you're on Anandtech I know you're more than smart enough to think of them independently - hopefully passing that wisdom forward

Best of luck, never stop asking why....

AxilleasT
*death or shock data googled with loose values used more to illustrate than talk electroshock peculiars....Slap me with corrections if you like*

 

[TuxDave]

Hey bud,
Some really colorful metaphors given, probably the most important take away unless you're held accountable for such measurements...

That said, and without beating it with derivations and some *basic/repulsive* (who you're asking) physics - here's a straight forwardish attempt at clarifying a relationship common people rarely can tell apart, or remotely care in all fairness.

So, the one with maybe the least ambiguity given the question, Voltage. As said, analogized, this metric is about the difference in electrical potential between two points (crucial) so that a current of one ampere traversing the plane ("imaginary force field" in between those points) expends 1 Watt(*will return to*) of power in the process = 1 Volt. Alternatively, a Volt can be defined as one joule/coulomb, as well as other equal definitions probably not beneficial in clarifying. Also, the units i used will come full circle in a second...

Now, a watt. Defined as a particle(object) held at a constant velocity of 1-meter/1-sec opposed by a force equal to one newton, resulting in the rate of work done = 1 watt. So, 1-watt=(1-Newton*1-Meter)/1-second <=> 1-watt=1-joule/1-second. Think of this as how "expensive" in terms of how much work an element, or object is to operate, as well as a way of setting a maximum before an object is "overworked" (or minimum). In circuits, or considering watt unit electrical measurements, if a lightbulb is given as a 50-watt rating - then when in a closed circuit it will be absorbing (taking work) from the source at 50-watt, where as the source will be (lets say its a one bulb circuit) providing (--50 watts) (perfect world).....where the sign identifies an element as receiving or supplying (+ receiving, -- supplying).

I've tried using as few of units not to belittle anyone, but just to bring the seemingly "evasive" definitions into the whole later on hoping to best clarify the difference between them. The remaining measurement, Ampere is a factor in electrical circuits concerning watts - as watts don't act alone in the whole picture, but more as a "demand." Leading us to the definition of 1-Ampere being approx. equal to getting a "bunch of electron charges" to pass a point in a circuit PER 1-second. More accurately, 1-Ampere=6.214x10^(18) electron charge carriers (electrons)/1-second. <=> 1-Ampere=1-Coulomb/1-second. This "bunch" or stupid-big number (if one electron were 1 penny, a coulomb would be $62.4 QUADRILLION dollars!!! yikes) might help answer your second question, how accurate are these.....

Well, I think you could imagine we're dealing with a huge quantity of ridiculously small electrons, each weighing ~9.1x10^-31 kilograms (which means nothing to me too - so if the "size" of that number, |9.1x10^31| were inches - it would be more than 2000x the diameter of what we consider the universe!!!!)

So to conclude with the hazards, and although we're "departing" my area as I'm no doctor, or really all too familiar with biology etc., I'll try sticking to the electricity involved. First, whether we're using AC or DC plays a huge role, point of contact, general cardio health, or even how sweaty a person happens to be, are also significant variables in the shock & death - using a rough values(DC) we can say as little as 500mA (dont let 500 fool you ...) or 0.5A can cause fibrillation and death. Now, disredgard any folklore like "the voltage doesn't get ya, its the amps!" yada yada....Remember, V=Amps * Resistance or more simply - they are both in the mix! SO think of it in terms of Watts which is P=v^2/r <=> P=Volt * Amp so if we only had 1/2 an Amp at 120V we'd be looking at a power rating in one second of 60 W - with 110W being a rough daily expended by an adult male. Also the same as 60V @ 2 Amps, or 30V @4 amps or a little more than the shock received from 200V with human resistance of ~ 2100Ohms....with people being "resurrected" using about 5V/cm (defib)....

I hope I clarified a pretty roundabout relationship....it's a lot of different quantities and actions that form as an equality (why it''s better to think, "It's the Electrons that'll kill ya") and i'd avoid thinking of it like the simile because if you're on Anandtech I know you're more than smart enough to think of them independently - hopefully passing that wisdom forward

Best of luck, never stop asking why....

AxilleasT
*death or shock data googled with loose values used more to illustrate than talk electroshock peculiars....Slap me with corrections if you like*

Impressive first post. I would welcome you to the forums except that you've hung around here for the last five years.

 

[AchillesT]

hahah... very true tuxdave, and thank you in any case for the warm welcome. There's so many incredibly knowledgeable members contributing on anandtech, I didn't mind being a "passive" member.