# Questions about fundamentals (voltage, and more)

Discussion in 'Homework Help' started by goatmilker, Dec 18, 2010.

1. ### goatmilker Thread Starter New Member

Dec 18, 2010
2
0
Ok, so.. I am a guitar player who Is interested in finding out how all of this works. It's pretty fascinating, however, It's raising quite a few fundamental question for me  and unfortunately I'm the type of person that can't skip ahead to a concept if I know that I don't fully understand prior concepts. So I was wondering if you all could help a noob out?

Here's what I'm stuck with:

1. Voltage. For some reason voltage is not really coming together for me, because I'm having a hard to relating the water drop example to the flow of electrons. Is voltage in regards to electrons the amount of electrons that jump to the next on a given swap? That doesn't seem right; that seems like charge. So then is it the speed that the electrons flow  that also doesn't seem right because I thought that this was all happening at a fixed speed of the speed of light. Speed does stay constant in a cable right? So then my last idea is, is voltage solely the amount of energy it takes to over come the next atoms resistance to change? How does that work with the example of clouds and ionization? It speaks of a clouds voltage rising, how does a voltage rise, and become more able to tear through the air?

 the reason the water drop isn't making sense is because that has to do with the speed the water is falling due to gravity, but I don't think voltage necessarily has to do with speed of electron flow. Does it?

2. The marble example. I'm confused when trying to imagine a few things. What if the cord is more that one atom thick, (which is always the case) how do the electrons flow in unison from the battery? The battery creates a surplus of electrons on one side, how does it distribute that surplus to the attached wire to create an even wall of flowing unison electrons? Why don't all of the electrons flow into one atom, then continue down one atom in the cable? Also, what decides if one electron flows from atom to atom or 300 electrons from atom to atom?

3. Lastly, when you create a surplus of atoms with a battery and then give it to an atom in the wire, that imbalance wants to inherently be corrected by the next atom and so shouldn't the electrons always flow through a wire even if the battery runs out after the initial imbalance? Why does the flow stop with the battery? I read that it is because the electrons will build up, but why is that not the case with static electricity with me and a doorknob? The imbalance doesn't just build up on my hand and stay there even after I touch a doorknob.

I know this is a lot, but I would be incredibly grateful if you could try and explain this to me. It would be a great Christmas gift for a stranger.

toodle pip,
ethan

2. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,938
1,089
The voltage is a potential difference, for example if we have on one end of a wire 300 electron missing and on the other end 500 electrons are missing.
Then we have the voltage between the two points.
Both these "points" are positive, but the first point (300 electrons missing) is negative with respect to the second point (500 missing electrons).
So everything is relative.
And if we connect these points with a conductive wire then current is star to flow. From more negative point to more positive point. And current will flow until the number of electrons on both ends will be equal (conservation of energy).
So current can be defined as rate of flow of a charge in an electric circuit.
And voltage is a electric pressure in water analogy.

3. ### amilton542 Active Member

Nov 13, 2010
491
64
when they use the water pipe as an example of electricity for voltage,resistance and current flow what they mean is, the current is how much water flows through the pipe, the voltage is how quickly the water is travelling through the pipe which is known as electrical pressure and and if you were to pinch the pipe to hold back the water it is known as resistance. the pinch of the pipe will hold back the water (current) but will increase the pressure (voltage). An increase in resistance will increase the voltage. Try out ohms law: voltage = current times resistance (V = I X R) . current = voltage divided by resistance ( I = V/R). resistance = voltage divided by current (R = V/I). give yourself a number for V I and R get yourself a calculator and watch how you end up with your numbers you chose

4. ### amilton542 Active Member

Nov 13, 2010
491
64
an electron flows from one atom to another atom because they have incomplete shells, it is a free electron and this occurs in all metals that conduct electricity , the atoms in the insulation around the cable have complete shells which means they dont have any free electrons so wont conduct electricity

5. ### goatmilker Thread Starter New Member

Dec 18, 2010
2
0
First, thank you for the responses.

According to this site's texts, resistance is not dependent on if the shell is complete or incomplete, it states that resistance depends on the elements hold on the electrons spinning around it. Which makes logical sense, if this were not the case things that filled up would never change again. This site's theory explains that metals have a looser grip on their electrons, and glass has a much tighter grip, and are therefore more resistant to change. This seems to be why my body has charge sometimes but not always, because if I rub my foot on carpet the pure friction of the action is causing electrons to change atoms  not necessarily because of incomplete shells that previously resided on my foot or the carpet.

Regarding the response to voltage  I understand conceptually what I can do to achieve a certain current by manipulating the voltage and resistance but, practically what is happening? Practicality is what kills me always.

Using your example, "if we have on one end of a wire where 300 electrons are missing and on the other end 500 electrons are missing" we have a potential difference. I get that but why does that have anything to do with pressure? Let's say we have 300 on one end and 2000 on the other end, the potential difference would be much higher, meaning a much higher voltage. But practically how is that related to pressure. Are the electrons moving faster to fill the difference? (I thought the cap here was the speed of light...) Or are more electrons moving at any unit of time? I just don't practically understand voltage.

6. ### hgmjr Moderator

Jan 28, 2005
9,030
214
We need you to stop multi-posting the same topic.

hgmjr

7. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Voltage is the 'force' which moves electrons. The speed the electrons move is not the speed of light. Electrons within a wire move very slow. It is the response of electrons to an applied voltage which is close to the speed of light. The speed of electrons within a wire depends on the cross sectional area of the wire and the material. Thus, if wires of different cross sectional area and material are connected in series (for example), electrons flow are different speeds through each wire.

Electrons do not flow evenly through a wire, it is the average flow which can be considered constant. Electrons, while moving in an average one direction (DC current), vibrate at a much higher rate.

In a battery, there are chemicals which react as to keep the surplus of electrons (voltage). When electrons flow into the positive terminal, chemicals insight the battery take these electrons and transfer them to the negative terminal.

8. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,938
1,089
When we have potential difference then electric field exist between to points. So this field is that force that "push" electrons.
And you have to remember that, if we have two similarly charged particle are brought near, they try to repel each other while to dissimilarly charges attract each other. So every charged particle has a ability to do the work thanks to repel/attract action .
And this ability of a charged particle do do the work is called electric potential.
And this "force" is electric pressure, becaues water flow thanks to water pressure and current will start to flow thanks to potential difference.
http://en.wikipedia.org/wiki/Coulomb%27s_law#Electric_field

Last edited: Dec 19, 2010
9. ### Fraser_Integration Member

Nov 28, 2009
142
5
Voltage is the rate of energy per unit charge.

When 1 Couloumb of charge (which is some amount of electrons) have 1 Watt of energy, that amount of charge has 1 Volt of voltage.

10. ### Fraser_Integration Member

Nov 28, 2009
142
5
the water "analogies" are just that, analogies. they're not perfect representations of electromagnetic forces. now you have a rough understanding of the topics, why not read more scientific examples and attempt to explain them to yourself? there are many high school level physics textbooks out there that your public library is sure to stock.