Ohm's law

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For any of you electronics enthusiasts, or even professionals, I have a question. How is there such a thing as high voltage-low current power, or high current-low voltage power with constant resistance? There is a linear relationship between the two according to Ohm's law, so why is it that eight AAA batteries (12v) do not put out the same amount of current as a car battery (also 12v)? Also, how is it that the voltage established by rubbing a balloon on your hair (several thousands of volts) does not produce enough current to run a light bulb? I have heard the power explanation (watts= v*a) but this did not make sense to me, because amperage is controlled by voltage assuming constant resistance, and thus so is power. Someone please make sense of this, I cannot find any worthwhile explanations anywhere.

Okay, so the basic relationship is E(voltage)=I(current)R(resistance)

An ampere, the basic unit of current is defined as

In layman's terms that's a lotta damn juice.

The difference between 8 AAA batteries and a car battery is that the AAA's simply cannot hold as much juice, therefore they CANNOT output as much juice.

Likewise, when you generate a static charge with your hair and a balloon, you create a huge difference in potential, but that potential usually discharges across a high resistance (the air gap between the balloon and ground) and like the AAA batteries it has very little "juice" to move.


If you have 12vdc or a 12,000vdc source and a unlimited supply of electrons to push, the current WILL be determined by the resistance of the circuit.


PS

Think of it in terms of water. Voltage is like pressure and current is like the volume/supply of water flow.

Your battery question is analogous to asking, "If my supersoaker can produce the same pressure as a fire engine, why can't they both fill my pool without a reload?"

I usually think of it as a highway. Voltage is the speed of the cars and current is the number of lanes. The watt is thus the number of cars passed per unit of time. So you can have few lanes but very fast cars or many lanes but slow cars but still get the same throughput.

The AAA batteries simply does not have what it takes to send out the same number of cars at the same time as a car battery.

Actually static electricity can light some low power LED, but there is just not enough energy to light normal bulbs.

Thanks you guys. I actually posted this just before stepping into the shower (for me the time at which my thinking capacity is at its greatest) and figured out exactly what you all just said on my own, but thank you so much for confirming what I postulated. This has been eating away at my conscience for so long now (having done electronics as a hobby for four years, and not yet truly understanding one of the very most fundamental principles). A weight has been lifted; my gratitude to all of you.

Don't feel bad. I know a lot of people who have trouble with this when they take up electronics....

......you know, if you had enough sets of 8 AAA batteries vvired in parallel, you could produce just as much current as a car battery.

DC electronics has its challenges but when you get into AC electronics and RF it gets crazy-I look at conductors like different sized garden hoses and larger and smaller water pipes-larger water pipes can carry more water than smaller ones and thicker pipes can handle higher pressure. The water is the "current" and the pressure is the "voltage"

The water pipe analogy is dead wrong. DC does not push electrons through a circuit like a pressure source pushes water through a hose. The small drift velocity of electrons in a circuit is a field effect

Use Google to get -Understanding Electricity and Circuits: What the Text Books don't tell you- by Ian M. Sefton, School of Physics, the University of Sydney.

See:
http://sydney.edu.au/science/uniserve_s ... sefton.pdf

You have to use fields and Poynting vectors to understand how a DC circuit really works. It is NOT like your garden host or water pipes and faucets.

AC gets a little trickier but it is still based on the same principles. The electrons that heat up the filament of your incandescent light bulb are already in the filament. It is the electrical and magnetic field that is moving them and very slowly at that.

ruveyn

It was a simple analogy not very detailed-it was how the idea was started when I went to school-then when I went on to more advanced schooling and semiconductors they spoke about electron flow and "hole" flow as traffic on the highway-it worked for me to get an understanding of it and the water analogy is a loose analogy at best.

If I called you on a Bell landline ruveyn, my analog pulse( signal) travels to Jersey very fast, via a field or flux, but what is the velocity of the electron drift, in and of itself?

0.001 mm/sec

The energy is carried by the field, not the electrons.

The electrons create the field which forms just outside the wire and is locally parallel to the war. The moving electrons creates a magnetic field which is around the wire and is locally orthogonal to the surface field. The Poynting vector which is the energy density flux points inward into the wire. It is the Poynting vector that carries the energy, not the electrons.

That is why current in a wire is not like water in a hose.


ruveyn

So we have 1000 seconds per meter. Or 16-17 minutes per meter.

To travel one mile , it would take 1610m X 16.66m= roughly 18 and 2/3 days.

I think I got a "C" in solid state physics so this might not be right, but IIRC the reason a phone works faster than that is because the wire is 'full of electrons' and when you push one in one end another one immediately (well, speed of information/light) falls out of the other end.

To make sense of the battery question, consider that the batteries have an internal resistance that needs to be figured in to the equations, this is why the AAA 12v cannot deliver the current of the car battery, they have a much higher internal resistance, measure the voltage drop across a car battery when you are cranking the engine and if you know the current drawn there is your car battery figure.

Now hook your AAA array up to the battery terminals and try and start the car, measure the voltage at the terminals, I'm guessing but it will probably be 0.5v or something..again if you know the current being delivered (you could safely insert a multimeter) you can establish the internal resistance of the AAA array cells, which to complicate things may even change when current is drawn, still ohms law will not lie.

Precisely. It is not the electrons that are delivering the energy, it is the electric field crossed with the magnetic field which produce the Poynting vector. Those slow moving electrons produce the magnetic field. All magnetic fields are produced by currents of charged particles. A simple DC circuit is more like a wave guide (the energy in the fields travel at nearly light speed). That is why you don't have to wait a half month after you turn on the lights to see the lights.

ruveyn

Never really considered electricity down to that level before..I'm imagining a sort of newtons cradle effect?

No. No. No. That is contact force. Electrical energy is delivered by the field, not by contact force.

Newton's Cradle is the same as the Garden Hose analogy. It is wrong.

Why do you think an electrical generator 100 miles away from your house, can turn on your lights nearly instantly when you close the circuit? The electrons are moving very slowly. 0.001 mm/sec. And with AC the electrons jiggle back and forth and get almost no where. All they can do is generate the magnetic field that surrounds the conductor connecting the generator (or battery) to your light bulb.

I curse and despise the Lie of the Garden Hose which is taught to millions of innocent pupils in school in the Name of Science. It is a disgrace.

ruveyn