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super basic quick question (grounded current)

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bulak

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The CORRECT eletron flux is from negative to positive, right?

In the picture above, the battery negative terminal is grounded (all eletrons should be going to the ground), how is it that a current can pass through the resistor then?

ps. I posted this question because I can't think of search keywords for this question on Google.

Thanks
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You have to learn this sometime. Ben Franklin got the charge on an electron wrong and thus most times the direction doesn't matter, but sometimes it does.

"Conventional Current" goes from positive to negative. Conventional current determines the sign of the potential difference.

Electrons, however, go the other way. it matters in electrochemistry. In solid state physics is matters too, we introduce another concept: holes go in the direction of conventional current.

We pick the "conventional current" method and when we really need to know which way the electrons are going, it's the opposite of conventional current.

I hope I answered your question. I always forget which way to mark the battery polarity.
 
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bulak

New Member
Yes, I know about the conventional current and holes stuff. I just would like to understand what happens in the picture above. Are electrons flowing from the positive terminal to the other ground somehow or are holes flowing from the positive terminal and being identified as positive current in the amp meter?

Thanks
 

Ratchit

Well-Known Member
bulak,

The CORRECT eletron flux is from negative to positive, right?
Physically speaking yes, but not when doing calculations.

In the picture above, the battery negative terminal is grounded (all eletrons should be going to the ground), how is it that a current can pass through the resistor then?
Physically speaking, the charges flow from the ground through the resistor and into the battery.

ps. I posted this question because I can't think of search keywords for this question on Google.
The first step in searching is to spell "electron" correctly.

KISS,

You have to learn this sometime. Ben Franklin got the charge on an electron wrong and thus most times the direction doesn't matter, but sometimes it does.
No he didn't. If he called the electron positive, what charge would a proton be? How about a hole in a semiconductor? Would that make it any easier to solve electrical current problems?

Current calculations should never be based on the polarity of the charge carrier. All calculations should be done by assuming that a positive charge flow exists from the positive pole of a voltage source regardless of polarity of the charge carrier. This is called a convention. Then after the calculations are done, the true direction of the charge carriers can be determined from their polarity.

Ratch
 

bulak

New Member
Physically speaking, the charges flow from the ground through the resistor and into the battery.
Beats me. I think this might be important for me to understand cases where the voltage is negative...

Phisically speaking, the positive battery terminal has a "stock of holes", correct? How is it possible that electrons flow from the ground, if it doesn't have a "stock of electrons", like a battery?
 

Ratchit

Well-Known Member
KISS,

I read your link. It says that Franklin chose a convention which was later redefined "by definition". No one can criticize Franklin for that. There is nothing about the two charges that say one charge or the other is "positive" or "negative". It is all definition. It could just as well be said that the two charges are black and white, or left and right. If you use the polarity of the charge to calculate a current based on its flow of charge direction, you will be wrong half of the time. That is because there are many charges of both polarities that move about. So engineers pick one agreed upon convention for calculation, and discern the true direction later if needed.

I see that the article is syntactically incorrect in that they use "current flow" when they should say charge flow.

Ratch
 

Ratchit

Well-Known Member
bulak,

Phisically speaking, the positive battery terminal has a "stock of holes", correct?
Physically speaking, no. Holes only exist is semiconductors. There are so many freely moving electrons in metal wires that a hole would be filled and annihilated just about instantly. The charge carriers of metals are electrons, not holes.

How is it possible that electrons flow from the ground, if it doesn't have a "stock of electrons", like a battery?
Electrons or other charge carriers flow around in a conducting circuit. If you want to designate part of that circuit as "ground", fine, do so. You can also use that point of the circuit (ground) to connect other circuits to it also. So ground is just part of the conducting path.

By the way, a battery is just a charge pump. Like a pump, it has to take in as many charge carriers (electrons) as it puts out. A fully "charged" battery or capacitor has as many net electrons as it did when it was not "charged". That is why I prefer the word energized instead of charged when referring to changing the energy level of the battery or capacitor.

Ratch
 

alec_t

Well-Known Member
Most Helpful Member
(all eletrons should be going to the ground)
No. Electrons repel each other, so move towards the more +ve potential, i.e. away from the ground.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Electrons are tricky little objects. The EMF causes them to move, but not necessarily "FLOW".

They will bump a nearby electron, heat the wire up, maybe emit some light (you will be hard pressed finding it), slow down and the electron it bumped will do the same. It's an endless set of collisions as long as there is a force acting on the electrons.
 

Ratchit

Well-Known Member
KISS,

Electrons are tricky little objects.
No more than any other subatomic particle.

The EMF causes them to move, but not necessarily "FLOW".
They move randomly without any voltage according to their thermal energy. When a voltage is applied and there is a conduction path, then they have a direction and speed called a drift velocity.

It's an endless set of collisions as long as there is a force acting on the electrons.
Electrons are always moving even without any force acting on them according to their thermal energy.

Ratch
 
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