Basic concepts

Thread Starter

bro

Joined Oct 26, 2013
9
Hi all

I would like to know what happens when the voltage in a given circuit increases.

The electrons flow faster?

Or they get more electrical charge?

Very appreciated.
 

adam555

Joined Aug 17, 2013
858
Assuming the resistance stays the same, then the number of electrons passing through the circuit increases proportionally to the voltage (I = E/R)
 

Thread Starter

bro

Joined Oct 26, 2013
9
adam555 thank you for your reply.

Now i will make some other questions if you don't mind.

So if that true, the amps increases too. Right?
 

adam555

Joined Aug 17, 2013
858
Go on; I don't mind...

Yes, the amps increase directly proportionally to the voltage; in accordance with Ohms Law:
\[I = \frac{E}{R}\]
Where...
I is the current in Amperes (A)
E
is the electric potential in Volts (V)
and R is the resistance in Ohms (Ω)​
 

Thread Starter

bro

Joined Oct 26, 2013
9
Very kind adam555

So how can we generate thousands of volts by rubbing ours feet in the carpet (i read this somewhere), and only liberate a few mA when we make contact with a conductor?
 

Thread Starter

bro

Joined Oct 26, 2013
9
hehe :)

Well hopefully someone here can give us the answer.
 

Thread Starter

bro

Joined Oct 26, 2013
9
shteii01 thank you for the link, but i have not the knowledge to understand the article.

So if you could give me an answer simplified, it would be great!

Appreciated
 

#12

Joined Nov 30, 2010
18,076
Rubbing your shoes on a carpet scrapes electrons off either you or the carpet. It depends on what materials are in action. The electrons create a high voltage but not much current.
 

Thread Starter

bro

Joined Oct 26, 2013
9
Rubbing your shoes on a carpet scrapes electrons off either you or the carpet. It depends on what materials are in action. The electrons create a high voltage but not much current.
I have read that too but i don't understand how that is possible. Since voltage is the driving force that impels electric current, when you get more voltage you get more current? Right? Am i missing something....
 

MikeML

Joined Oct 2, 2009
5,444
Your body acts as one plate of a capacitor. By rubbing your feet, you are separating charge (moving electrons); missing electrons in the carpet, extra electrons on your body.

Each electron carries charge. Stored charge is measured in Coulombs. One electron carries −1.602176565(35)×10−19 Coulomb of charge.

The voltage that appears across a charged capacitor can be found by transposing this equation: Q=CV, or V=Q/C. If C is small, the Voltage can be very large.

As your body discharges via a small arc, the current is carried by the ionized air in the arc, the effective resistance of which can be quite high. The Peak current is limited due to Ohms law. The duration of how long the current flows can be determined by Q=It, where I is in Amps, and t is in sec.
 

#12

Joined Nov 30, 2010
18,076
I have read that too but i don't understand how that is possible. Since voltage is the driving force that impels electric current, when you get more voltage you get more current? Right? Am i missing something....
How is it possible to scrape electrons off a surface? Because electrons are real physical objects. How is it possible to scrape jelly off a piece of bread?

When you get more voltage, you get more current through a fixed resistance. The fixed resistance is what you missed. Air doesn't have a fixed resistance. It has resistance per distance.
 

Thread Starter

bro

Joined Oct 26, 2013
9
Your body acts as one plate of a capacitor. By rubbing your feet, you are separating charge (moving electrons); missing electrons in the carpet, extra electrons on your body.

Each electron carries charge. Stored charge is measured in Coulombs. One electron carries −1.602176565(35)×10−19 Coulomb of charge.

The voltage that appears across a charged capacitor can be found by transposing this equation: Q=CV, or V=Q/C. If C is small, the Voltage can be very large.

As your body discharges via a small arc, the current is carried by the ionized air in the arc, the effective resistance of which can be quite high. The Peak current is limited due to Ohms law. The duration of how long the current flows can be determined by Q=It, where I is in Amps, and t is in sec.
Thank you for your reply it seems very pro but i need to look very well at it and reach some conclusion.

Very nice from you
 

Thread Starter

bro

Joined Oct 26, 2013
9
How is it possible to scrape electrons off a surface? Because electrons are real physical objects. How is it possible to scrape jelly off a piece of bread?
.
I have read that too but i don't understand how that is possible (The electrons create a high voltage but not much current - Was this fact that i don't understand). Since voltage is the driving force that impels electric current, when you get more voltage you get more current? Right? Am i missing something....
 

adam555

Joined Aug 17, 2013
858
I have read that too but i don't understand how that is possible (The electrons create a high voltage but not much current - Was this fact that i don't understand). Since voltage is the driving force that impels electric current, when you get more voltage you get more current? Right? Am i missing something....
Yes, but remember that you also have resistance in that formula; so, if you increase the voltage, but at the same time increase the resistance proportionally, you will end up with the same current -the same amps-.

For example:

1 Volt / 1 Ohm = 1 Amp

and

1000 Volts / 1000 Ohms also = 1 Amp

You see now how you get the same amperage with 1000 volts difference? In the same way you can have a high voltage and a low amperage.
 

Thread Starter

bro

Joined Oct 26, 2013
9
Yes, but remember that you also have resistance in that formula; so, if you increase the voltage, but at the same time increase the resistance proportionally, you will end up with the same current -the same amps-.

For example:

1 Volt / 1 Ohm = 1 Amp

and

1000 Volts / 1000 Ohms also = 1 Amp

You see now how you get the same amperage with 1000 volts difference? In the same way you can have a high voltage and a low amperage.
Now every thing starts to mais sense :) finally i should say. Very appreciate to ali of you that reply to this post.
 

WBahn

Joined Mar 31, 2012
24,572
In some ways, the separation of charge when materials rub together is very similar to what happens when a semiconductor p-n junction is formed.

Imagine two substances, say someone's hair and a rubber balloon. The hair's chemistry is such that their are weakly bound electrons associated with each molecule and, except for the attraction to the net positively charged molecule that would result, the molecules would just as happily get rid of. The rubber balloon, on the other hand, is the opposite. It's chemistry is such that it pretty tightly binds all of its electrons and would love to bind a few more, except for the repulsion of the extra electrons that would result from the net negatively charged molecules that would result.

When the two objects are brought into contact, some of the loosely bound electrons in the hair migrate to the spots on the balloon that want to grab electrons. Because the two surfaces are in contact (and only the molecules at or very near the surface participate), it is as though the two materials, at the specific points of contact, are actually one chemical compound that is ionically bonded together (in essence, they really are) and so the slight charge separation is not a big deal because the material, overall, is still electrically neutral. But now the materials are pulled apart and the electrons that migrated from the hair to the balloon don't have time to migrate back in response to the increasing voltage due to the increasing charge separation and, as a result, get trapped on the balloon leaving it negatively charged and the hair positively charged.

The answer to another part of your question requires a quantitative look at things and not just a qualitative one. The reason is that it takes a very tiny amount of charge to result in a very large voltage, but it takes the motion of a very large amount of charge to result in even a very small current.

This blog entry might help: A Battery isn't a Capacitor!
 

russ_hensel

Joined Jan 11, 2009
825
In the case of static electricity it is usually the case that voltage is high, current is low, charge is low, resistance is high, and capacitance is low. Static electricity is the same as any electricity, but with quite different parameter values than most "current" electricity situations.
 
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