I've seen a few ways to think of voltage, amperage, watts, and resistance.

Things tend to stick better with me if I come up with my own variations, and since I'm already good at thinking of the components of kinetic energy, let me run the following by you and please let me know how far off I am:

Volts --> velocity

Amps --> mass

Watts --> energy

Ohms --> I wanted to say density of medium here, but that doesn't really work. It's more like difficulty of movement right? Resistance kinda nails it without any change required I guess.

Thanks

In fluid dynamics it would be:
Volts->Pressure/Pounds per square inch
Amps->Gallons per minute
Watts->Power/Horsepower/Work
Ohms->orifice or restrictor plate

Voltage is more like water pressure. Your faucet has pressure built up behind it, but until you open it, no water flows. Similarly, there is 110 volts at your light bulb, but no current flows through the bulb until you switch it on. Amps are a measure of current flow. Ohms are a measure of resistance to said current flow. Watts are volts times amps.

stoic-one has a good approach. I tend to think of it a little differently, but I don’t know which is closer to reality.

I think of it as:
Volts - size of the pipe.
Amps - the rate at which the water is flowing through the pipe. Not gallons or liters per minute, but if you could put a pig in front of the water, how fast would the pig move in feet per minute.
Watts - power, how many gallons or liters of water moved.

With four times higher voltage (4x larger pipe volume) and one fourth the amperage (1/4 the flow rate) you’ll still move the same amount of water.

Of interest, Ohms of resistance are relative to amperage or current flow, not voltage. This is why transmission line are higher voltage. By raising the voltage, one can send the same amount of electrical power with less current.

This seems somewhat similar to pumping the same amount of water more slowly through a larger pipe rather than more quickly through a smaller pipe as the slower the water is moving through the pipe the less friction.

I tend to work with 120 / 240 volt wiring things up, 480v changing fuses occasionally on the well pumps*, and extremely high voltages on the temporary net electric fencing that I use to graze the goats in different spots.

With 120/240 I’m careful, but not too worried.

With 480, I am extremely paranoid, not touching anything until I have: 1) First visually verified that all three blades of the disconnect have come out when I dropped the handle, then 2) checked voltages with a meter to assure that then is no voltage even though I have already visually verified that the line voltage is disconnected.

With the much higher voltage electric netting I hardly worry about it at all. The voltage is much higher, but there is almost no current and it is pulsed. Is it unpleasant when you get bit by the electric fence? Absolutely. Is it going to cause lasting damage to a human or most animals*? Nope. The voltage is extremely high, but the current or amperage is almost nonexistent.

*For some reason the electric netting seems to be rough on toads, but nothing else seems to have trouble.

quote:

Originally posted by slosig:
Of interest, Ohms of resistance are relative to amperage or current flow, not voltage. This is why transmission line are higher voltage. By raising the voltage, one can send the same amount of electrical power with less current.

This is a little off.

First, Power = Voltage * Current. That the same amount of power at a higher voltage requires less current has nothing to do with resistance.

Second:

> Ohms of resistance are relative to amperage or current flow, not voltage.

Resistance is meaningless without both voltage and current. Voltage = Current * Resistance. If you put a certain voltage across a certain resistance, a certain amount of current will flow. If you push a certain amount of current through a certain resistance, a certain amount of voltage drop will occur.

What I think you were getting at, however, is that when current flows through resistance, there is energy loss (as heat).

The power dissipation across a resistance comes from combining the V = I*R and P = V*I equations: P = (I*R) * I --> P = I^2 * R. The power loss is proportional to the SQUARE of the current flow across the resistance.

You can also solve it as P = V^2 / R, but that is less useful here because the voltage in question is the voltage DROP across the resistance, not the overall voltage, which is fine you have a physical system you're measuring, but is a pain to figure on paper.

Transmission lines operate at extremely high voltages to reduce the required current to reduce resistive power dissipation.

https://en.wikipedia.org/wiki/...aw#Hydraulic_analogy
Worded differently, of course, but identical to what stoic-one said above.

Technically, the "quantity" of electricity (charge) moved per unit of time is a "Coulomb". One Coulomb is the amount of charge moved by a current of one Amp in One second. The water equivalent would be like "gallons per hour".

ETA: I see this is covered in the link provided by egregore, which I had not perused.

flashguy

Where the water pump/pressure metaphor falls down is that electrical flow is governed more by the "pull" rather than the "push." It is the motor/heater/whatever that "consumes" the power that regulates the volts/amps needed to exercise it. "Flow," "governed," and "regulates" are not actually accurate words to use, but it might help in evaluating what is important in an electrical circuit.

^^^
Excellent.

Your mechanical analogy is a good start, but amps is not mass. Amps measures flow. In other words, it's a rate of change. And Ohms is a bit like difficulty of movement, but that's not density. A better mechanical analog might be drag, or friction.

A good analogy to get started with is a hose. (That's what they used in engineering school back in the day, anyway.)

Voltage is analogous to water pressure. This should be intuitive - the more water pressure in a given situation, the more flow.

Resistance is analogous to the drag put on the water flow by the hose - smaller diameter, longer length of hose = higher drag. If you put a long, thin hose on the water supply, you'll get a trickle. Put a short, fat hose on the same water supply, and stand back. (Trust me when I say you don't want to get into the equations or unit measures for flow resistance.)

Current (amps=coulombs/sec) is analogous to flow rate (gal/sec).

If you want more flow through the hose (increase the amperage), you can either get a thicker hose or a shorter hose (reduce the resistance) or up the pressure (up the voltage).

This should give you a start. They didn't have fluid analogs for some of the next sets of ideas (capacitance, inductance etc.) that you'll come across in electrical analysis, but by then hopefully your intuitive grasp of R, V and C will see you through.

Twinkle, twinkle, little star.
Power equals I-squared R.
If it's voltage that you need,
Drop the square to do the deed.

To further explain my process, loosy goosy as it is...

The hose analogy is what I've seen before too, and I can see why it is a good way to describe what's going on.

When I was playing with the terms in my head it occurred to me that since watts is a measure of the multiplication of volts and amps it started to look like kinetic energy needing velocity and mass. From there it seemed like the push of volts was more like velocity than anything else, and likewise the amount, or amps, was akin to the mass. Also, volts and velocity obviously start with v so it made it a tad easier on my noggin to store it.