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question: how fast do electrons accumulate at the negative end of the battery lead


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I am studying electrical engineering again and have read that the electrons travel from the negative lead to the positive one at a very slow velocity. Now the book states that in order for the mechanism for voltage to work an electron accumulation or "build up" occurs at the negative lead and when a non-zero resistance in placed between the positive and negative leads an impulse of energy is sent through the conductor which connects the positive and negative ends of the battery.

My question is, as seen from the title, if that pulse happens continuously then how fast are the electrons building up or accumulating at the negative end of the battery. What would this depend on?

My guess is that it must be happening pretty fast in order for a pulse to occur then there must be some difference. My guess is also that its not a continuous pulse but instead a discrete pulse because the electrons are being re-accepted back into the positive lead of the battery. 

 

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First question, If you are studying electrical engineering, why post in Physics, not Engineering ?

The short answer to your question is that negative charges do not 'travel to or accumulate around the negative terminal' in either the Engineering model or the Physics/Chemistry model of the physical processes that are going on.

I wonder why the book said a non-zero resistance ?
The smaller the resistance the bigger the energy pulse!
And zero resistance (an engineering short circuit) will result in a flash and some melted metal.

Please confirm which model you want to work on, they are quite different and meant for different purposes.

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45 minutes ago, studiot said:

First question, If you are studying electrical engineering, why post in Physics, not Engineering

I posted in the physics because I was unsure of the section and was not thinking at the time to place it in the engineering section.

 

46 minutes ago, studiot said:

Please confirm which model you want to work on, they are quite different and meant for different purposes

I want to work on the electrical engineering model. 

 

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Also seeing that you are correct that this would be an engineering question rather than a physics one, would it be possible for this thread to be moved there so that no confusion comes of this in the future.

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3 hours ago, ALine said:

I want to work on the electrical engineering model. 

So the electrical engineering model it is.

The engineering model is designed and intended to make things (electical equipment in this case) work.
Engineers only delve into the finer points as far as they have to.

So the model is based on two physical quantities, current and voltage.
Other physical quantities such as conductor length are normally considered immaterial.
The two quantities are further split up into currents and voltages in different parts of the equipment (called circuits) and the external effects on the environment (called loads or inputs or outputs).

Sufficient (simultaneous) equations introduced to fully calculate conditions in the circuits, though short cuts are often availble if a full solutuon is not rquired.

The circuit is represented by a collection of points (called nodes) at which the voltages are calculated

and links or paths between the nodes through which the current flows; with each path having 'circuit elements' offering specific properties.
These properties are stated in terms of coefficients applied to the currents passing through the link and the voltages appearing between specific nodes so that the already mentioned equations can be stated.

Now the thing is that it does not matter to electrical circuit theory what a current is made of or how it works, it just matters that the currents and voltages follow the model or idealisation.

And, of course the currents may be direct or alternating or transient (your pulse you asked about). In alternating current there is of course no positive or negative in the same way as with direct current.

 

How are we getting on ?

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So far so good.

If I am understanding you correctly from an engineering "lens", so to speak, I do not need to worry about the "physics" in terms how everything "works" but instead I only really need to understand how to use and apply the models.

 

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6 minutes ago, ALine said:

So far so good.

If I am understanding you correctly from an engineering "lens", so to speak, I do not need to worry about the "physics" in terms how everything "works" but instead I only really need to understand how to use and apply the models.

 

Excellent.

I'm sorry my post was so stuffy and 'theoretical'.

The rest is much more practical.

Now I mentioned 'circuit elements'

These are ideal black boxes  -  ideal in that they 'do what you want but you don't have to know how or why'.

The element or box has one, two, three or four or sometimes many 'terminals' with which it interacts with the rest of the circuit elements via the nodes.

One terminal is special  - I only know of one example we call ground or earth.

Two terminals are simple so let us take one of those.

Say we connect one terminal to node A and the other to node B.

Ohm's Law tells us that the current though this element is given by the product of a coefficient (called the conductance) and the voltage difference between nodes A and B.
Of course the conductance is the reciprocal of the resistance for direct current or the reciprocal of the impedance for alternating current. (note the voltage difference between A and B may or may not be changing as a result).

Other two terminal elements are voltage sources and current sources.

Three terminal circuit elements allow three nodes to be accessed  - examples are transistors thyristors etc.

Elements called 'Four terminal networks' are really the bee's knees. Nearly every circuit element your could think of can be modelled by a four terminal network  - transformers, motors, radio antenna, amplifiers, transducers and interestingly two, and three terminal networks (elements)

I don't know where you are at in your EE studies  - some of this you may have heard of, some not so ask if I am introducing stuff you haven't met before.

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I am good, so far everything has been a good review of what I have learned when I was taking EE classes in uni. It also helps because I did poorly in those classes because of reasons and you explaining it in this step by step manner really clears things up.

I was unaware that four terminal networks could be used to model a large amount of circuit elements.

Also for better reference of my current EE knowledge I am good up until amplifiers and transistors. Also I have to go back over Thevinen and Norton circuits. Hopefully that helps.

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