How Does Voltage Influence Electron Behavior?

[Windell]

Can someone please tell/explain to me how voltage affects electrons. Does it determine the speed of the electrons in a conductor? Is so why a power supply rated 12v 3A and another rated 9v 3A have the same amount of electrons traveling at the same speed through the conductor. My big question is: What is the purpose of the deference in voltage?

 

[anorlunda]

I hate the water analogy, but it may help you. Think of a water hose. Voltage difference one end of the wire to the other, is like the pressure difference one end of the hose to the other. Current in amps is like the flow of water in the hose in liters per second. The power is voltage times current. You need both voltage and current to get power.

It is best to forget about electrons. They just confuse people. Electrons are not like little capsules of energy nor is a cup full of electrons like a cup of water.

 

[jim hardy]

The water analogy leads one to the mistaken idea that like water, electricity always falls to ground.
But that's gravity not electrical attraction..

It takes a long time to get one's thinking aligned so that such apparent conflicts resolve.

I suggest that at hobbyist level Bill Beatty's articles are very useful. That's because he explores one by one the logical conflicts that arise from less-than-perfect methods of explanation.

Sample:
from https://www.electrical-contractor.net/ESF/Why Electricity is Impossible to Understand.htm
but
his website is http://amasci.com/ele-edu.html

ELECTRIC FLUID
Electricity is impossible to understand because of...

...mistakenly believing that electric circuits are analogous to open
hydraulic systems (pouring a cup of water through a pipe) when they
actually behave like closed hydraulic systems: a drive-piston connected to
a driven piston, with the connecting hoses pre-filled with water. This
probably comes about in part when we teach that circuits are like pipes
with water, but students then imagine the faucet at home, rather than the
hydraulic system of a backhoe.

...mistaken belief that the fluid analogy does not apply to circuits
because in wires the ENERGY flows, while in pipes the flow is of a
material. Mistaken belief that the "fluid" in wires always flows at the
speed of light, while in pipes the flow can be fast, slow, or stopped.
Mistaken belief that the "fluid" in wires flows from the source to the
load and does not return, while in pipes the water circulates around and
around. This is all incorrect. Actually the "electric fluid" in wires
flows slowly, not at the speed of light, just as happens in water pipes.
In wires, the "electric fluid" flows slowly while the energy flows fast,
just as happens in water pipes. And in wires the "electric fluid" flows
slowly in a circle, just as happens in a pre-filled hydraulic system.

...the lack of a good name for "cancelled charge." When + and - come
together, the result is NOT nothing. The result is matter. The result
can also be the cancelled-but-mobile "electric fluid" found in all
conductors. Since matter contains (is even MADE of) "cancelled charge,"
and since electric current in wires is a flow of "cancelled charge," we
should see matter as being made of "non-moving electric current." Matter
is made of "frozen electricity." The exception is conductors, which
contain "liquid electricity." Some common names for the neutralized
mobile charges found in conductors:
Electron sea
combined charge
canceled charge...

old jim

 

[Windell]

How do you calculate the power output of a generator. I know that P = I x E and that you can know the output voltage but how do you calculate the current in order to determine the power output?

 

[anorlunda]

Actual power out depends on the actual load connected to the generator. If the load is a resistor R, then I=E/R

Maximum power out is limited by heating of the wires. Look at the name plate for max power of max current.

 

[sophiecentaur]

Does it determine the speed of the electrons in a conductor

Firstly, the speed of electrons (the mean square drift velocity) is extremely low (around 1mm / s.
This link tells you the whole story about charges flowing through a uniform wire. You can see the drift velocity is proportional to the PD (Voltage drop) across a length of wire but it's so low that the Kinetic Energy is just not relevant as a mechanism to transfer power.

 

[sophiecentaur]

How do you calculate the power output of a generator. I know that P = I x E and that you can know the output voltage but how do you calculate the current in order to determine the power output?

You have to get your thinking in the right order if you want to suss this out properly. It's all a matter of cause and effect and carts coming AFTER horses. The energy source in a circuit is the Battery (etc. etc.) and it is the Potential Difference (Voltage) that counts. It tells you the Energy available for each unit of charge. You put a load across the battery (Resistor, say) and that will give you the current that flows. If you want to determine what Resistance is needed for a particular current to flow, that's quite possible of course but what you end up with is not a simple cause - effect thing but a "what do I have to do to get that cause to have this effect?"
You can only know the output power that a generator is actually supplying by knowing the V and the I that happens to be flowing - but that's determined by the load and not the generator.
On a higher level, you can calculate the power that the Generator could supply by knowing details of the design like the magnetic field, the resistance of the coils and the power of the engine (etc.) that's turning the generator. (That's another cause and effect thing). The resistance of the coils can give you an indication of the possible current available before they overheat but that's a practical thing.
So you need to be very precise in your question(above) to get an answer.

 

[jim hardy]

I know that P = I x E and that you can know the output voltage but how do you calculate the current in order to determine the power output?

You can only know the output power that a generator is actually supplying by knowing the V and the I that happens to be flowing - but that's determined by the load and not the generator.

If Load = R then current I = E/R .

 

[analogdesign]

I've never understood why people hate the water analogy so much. Like any analogy, it is incorrect in a holistic sense, and it has its limitations, but for a lot of purposes it helps develop a lot of intuition about electric circuits.

Also, I disagree with Mr. Beatty's point about canceled charge resulting in matter. That simply isn't true. The matter is always there. In a semiconductor, a minus charge is an electron and a postiive charge is a hole (a kind of lack-of-electron) in a lattice site. So, when a - meets a +, they really do cancel in an electrical sense and make no more matter because the electron was already there (it just wasn't in the thrall of a particular atom). Calling it "frozen electricity" makes no sense, as there are still electrical interactions between the electrons in the various shells and the protons in each nucleus (and surrounding nuclei since the each outer shell electron has an excursion radius of several lattice constants so it interacts with a handful of nuclei). Indeed, I think this analogy is more misleading that the hydraulic analogy.

I guess this goes to show that all "analogies" are flawed. The only way to really understand electric circuits is through Maxwell's Equations and the only way to really understand transistors is through Quantum Mechanics. However, you can do useful things without "really understanding".

 

[jim hardy]

However, you can do useful things without "really understanding".

Yes , one can provide valuable service to industry with just enough understanding of how things work to keep them in good repair and running smoothly..

It's a different skillset.