# Having trouble understanding amps, watts, voltage, and how they all work [duplicate]

I read that watts is amps multiplied by voltage.

But then I read that it depends on the wattage ... what determines wattage? I thought that the outlet supplied voltage potential, and the device uses that. How do amperes, watts, etc. come into the whole big picture?

I also found that you need to know how much resistance is in a circuit to determine how many amps equals how many volts. How would one know the resistance beforehand throughout an entire circuit before figuring out wattage? I thought wattage was force.

Then I read that a volt is what "pushes" electrons, but then I read that wattage is a force equal to one joule per second.

How does it make any sense to understand that voltage is the power when wattage is considered force? There's two forces?

Assume I do not know the wattage, what is the amperes of one volt then?

I have tried books, Google searches, everything - it doesn't add up to me.

This doesn't make sense to me, and it's greatly complicated. Ironically, I've done some small electrical projects not knowing this, and it's unclear to me.

Can anyone make this clear(er) to me?

• Where did you read that "it depends on the wattage"? Can you give us a link and some context? – The Photon Dec 23 '13 at 22:17
• I read it on some web page through random searches regarding this. Sorry, but can't find it at the moment. I believe it was a forum or such about electrical engineering. – Eax Master Dec 23 '13 at 22:20
• Amperes = flow, volts = potential, watts = power, joules = energy. – Ignacio Vazquez-Abrams Dec 23 '13 at 22:30
• Your question is extremely broad and it will be hard for anyone to cover everything you mention. Could you create a new question that is very specific, and includes the background information that prompted the question? – Joe Hass Dec 23 '13 at 22:34
• I doubt anyone can make it clearer than what you can find in books and Internet research. Perhaps you lack the physics background to put it into place. The Watt is a unit of energy per time, and energy in the context of electric circuits is the work required to move charged particles through an electric field. If you don't have the physics background, then you can still memorize the formulas, but the intuition behind them will be missing or incomplete. How far did you study physics in high school? – Kaz Dec 23 '13 at 23:02

I read that watts is amps multiplied by voltage.

This is correct.

But then I read that it depends on the wattage ... what determines wattage?

It depends what kind of device you're talking about. Some devices may have a power (wattage) limit different from their voltage or current limits. As an example, overloading the power (wattage) might cause the part to fail from burning up due to high temperatures, while overloading the voltage might cause the part to fail due to sparks crossing between conductors that aren't meant to be connected.

I thought that the outlet supplied voltage, and the device uses that.

The outlet of what? If you're talking about a power supply, this is true except in special cases.

How do amperes, watts, etc. come into the whole big picture?

Usually a power supply will provide a (mostly) fixed voltage output. The load will determine the current drawn. Unless it tries to draw more current than the supply is able to provide, in which case the supply voltage might sag, or the supply might fail.

I also found that you need to know how much resistance is in a circuit to determine how many amps equals how many volts.

This is only true if your circuit is made up only of resistors. More generally, different loads will draw a current that depends on the voltage supplied. You have to look at the datasheet for each part to find out what that current is and how it depends on voltage.

I thought wattage was force.

This is entirely wrong. Wattage is power. Power is the rate that work is done, or the rate of energy being transformed from one form to another. For example, transforming electrical energy into heat, or transforming chemical energy into electrical energy.

A supply that provides more power can supply energy more quickly. A load that draws more power requires energy be supplied more quickly.

Then I read that a volt is what "pushes" electrons ...

This is more or less right. A gradient of voltage produces a force on a charge carrier.

... I read that wattage is a force equal to one joule per second.

This is nonsense. A joule per second is a unit of power, not force. One watt is equal to one joule per second.

How does it make any sense to understand that voltage is the power when wattage is considered force?

It does not make sense. Wattage is not force.

Assume I do not know the wattage, what is the amperes of one volt then?

It depends on the load or device. If you read the datasheet of a given device it will tell you the required current (amperage). If you have a resistor, Ohm's law applies: I = V / R.

Can anyone make this clear(er) to me?

We'll do our best, but it sounds like you are having trouble grasping the fundamentals. I'd recommend finding a single, reputable book that explains this material and read that, rather than trying to learn from a bunch of different random websites that might be written with different expectations about the reader's level of knowledge.

• I have tried, believe me, and I still don't get it. As mentioned, I'm not new to the whole idea of engineering. I've actively done small projects, programmed computers, researched datasheets, done Assembly programming. But these specifics never were needed for rudimentary work. I wish to learn them, but I appear to not be able to understand this, and this will limit my goals. Your answer doesn't paint a much better picture for me. – Eax Master Dec 23 '13 at 22:33
• Key point: Watts measure power. Volts measure electrical potential. They are not the same. – The Photon Dec 23 '13 at 22:35
• Key difference between power and potential in this context? That doesn't sound like an explanation. The wall outlet provides "potential", but doesn't provide power then? The device gains "power" from "potential?" This doesn't add up. Wall outlets are understood to have "voltage", which is potential, correct? So the outlet doesn't supply power (wattage), but the device provides wattage from where/how with potential? – Eax Master Dec 23 '13 at 22:36
• If a location in space has a electrical potential of 1 V, it means that if there were a 1 C charge at that location it would have 1 J of energy. To get 2 C of charge there, you'd need 2 J of energy. But if there's no charge there, there's no energy in the system, although the potential is still defined. – The Photon Dec 23 '13 at 22:42
• That doesn't make much sense to me still. If the potential is all the wall provides, where does the power/energy derive from, come to do, and how are amperes measured within potential itself? Where does wattage's power come from? – Eax Master Dec 23 '13 at 22:43

When you turn your water tap on water flows. If you turn your tap nearly off it trickles out. Try this: -

• Water pressure is like voltage
• Flow of water is like current
• The tap is like a variable resistor controlling the flow.

Voltage divied by resistance is current just like in a tap; pressure divided by resistance equals flow rate.

$I=\dfrac{V}{R}$ - this is ohms law - more voltage = more current; more resistance = less current.

Even in hydraulics power is the same i.e. flow rate multiplied by pressure = power.

Power = volts x amps ($P = V.I$)

Can anyone make this clear(er) to me?

Maybe an analogy will help? Consider the mechanical analogy where

voltage $\leftrightarrow$ force

current $\leftrightarrow$ speed

Now, the product of force and speed, like the product of voltage and current, is power, the rate at which work is done.

The Watt, a unit of power, is thus not a force, it is a measure of "how fast work is being done".

Recall from elementary physics that work is done by a force acting through distance. For a constant force, the work done is simply the product of the force and the distance.

Clearly, no work is done by a force that does not act through a distance.

Analogously, no work is done by a voltage that does not act on electric charge.

Thus, the voltage between the terminals of an "outlet" does no work unless there is a circuit connected that allows charge to flow. And the power, the rate at which work is done, depends on the circuit connected to the outlet.

If the circuit allows a "lot" of charge to flow, for a given voltage, the associated power is larger than for a circuit that allows a "small" amount of charge to flow.

So, if you connect a small resistance to the outlet, there will be a large current and the associated power will be large. If you connect a large resistance, there will be a small current and the associated power will be small.

• You have to have a clue to "consider the mechanical analogy". I do not detect the presence of a decent physics background in OP, which is perhaps the reason why books and internet research aren't helping. – Kaz Dec 23 '13 at 23:03
• @Kaz, I suspect you're correct in your assessment of the OPs background but do keep in mind that others, with the proper background, may read the answers here and gain some useful insight even if the OP doesn't. – Alfred Centauri Dec 23 '13 at 23:43