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Voltage and Current Understanding

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nicksydney

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I've been battling to understand in simple terms how Current and Voltage 'works' in a circuit because for some reason I'm getting myself confused everytime I read the definitions and reading a circuit and then trying to create a circuit.

This is how I think of Voltage and Current :

I think of Voltage as 'the pressure that is being applied to a circuit that "push" Current around the circuit loop. It starts from a given point as X amount and returns back to the same location with the same X amount. During it's journey through the circuit this pressure increase or decrease depending what stands in between. The pressure are applied across all the different part of the circuits but what's difference is the amount applied to the different part.'

I think of Current as 'small particles that carry charges and Voltage is the pressure that are applied to "move" around these charges. The "number" of this particles are reduced or increased depending our needs and depending (using the appropriate components - i.e. using Capacitor increase it while using Resistor to decrease it).'

The way I see Voltage is like the transportation for the Current where it "drives" around to every corner of the circuit making sure that each part of the circuit "received" Current.

Input and feedback are very much appreciated.


P.S. Sorry if the question or analogy sounds stupid :)
 
You might be confused by the fact that anything other than the very most basic components are not linear in their charge transfer characteristics.... This is why electronics exists.
 
nicksydney,

Yes, you do need to have a better understanding of voltage and current. We start out with electrical charge. Wires have a large preponderance of electrons, each of which have a unit negative charge. Other subatomic particles like ions have may have a positive charge. Like charges don't get along too well. They repel each other. So it takes energy to bring like charges together. The more charges are crowded together, and the closer they are crowded together, the more energy it takes. If you divide the energy it takes to bring the charges together by the number of charges, you get a unit energy density. This energy density is called voltage, and the units are joules/coulomb.

It is well known in physics that energy will move from a higher energy lever to a lower energy level. So charges (electrons) with a higher energy density (higher voltage) will try to move toward a location of lower energy density (lower voltage). This is what causes charge flow to occur in a conductive circuit. So the movement of charge is not caused by "pressure", but instead by energy diffusion.

Anytime a charge moves, by definition you have a current. Current is charge flow, and "current flow" is a misnomer that means the ridiculous phrase "charge flow flow". Current has a direction and exists, but it does not flow twice.

Batteries and other voltage sources increase the energy density at one terminal and lower the energy density at the opposite terminal, thereby causing charge to flow and current to exist. If the charge flows through a resistance, some of the energy is dissipated as heat, so that there is less energy where the charge leaves the the resistor. Since the same number of charges leave the resistor as enter it, that causes a lower charge density (voltage) and is sometimes referred to as "voltage drop".

I think you will be better off if you forget analogies and stick to what really happens electrically. Especially the prevalent "water" analogy so often taught. So think of circuits in terms of energy and forget "pressure". That is just my opinion. Ask if you have any more questions.
Ratch
 
Your analogy is flawed. Current is flow. You can think of it as the flow of charge, but that's even slightly wrong. The water analogy really only works for resistive circuits, but it is a place to start.

See here:
 
Voltage does not return with the same "X" amount. The voltage is actually "dropped" across each component in series from the positive to the negative. The sum of the drops equals the source voltage. The drop across each component is equal to the current through the component times the impedance of the component.

Current is the same value in all components in series. The number of charges involved is very large and is generally immaterial for most circuit calculations. The number of charges is not changed by a resistor or capacitor, but they do affect the flow rate (current or number of charges per second that move through the device).
 
understand in simple terms how Current and Voltage 'works'

If you want it in simple terms, you have a 12v battery connected to two resistors in series.

At the top of the first resistor we have 12v.

The next thing you say to yourself is this:

A voltage will be dropped across the top resistor according to the current flowing and the vlaue of the resistor.
To find the vlaue of the voltage we apply a law called Ohm's Law such that the voltage dropped is equal to the current flowing (in amps) multiplied by the resistance of the resistor (in ohms.)
Take the result from 12v and you have the value of voltage at the join of the two resistors.

Don't get yourself involved with "pressure" and "flow" and "electons"

Now explain to me a 12v globe and resistor connected in series to the 12v battery.
 
Hi Nick.

You are basically correct when you say that Voltage is the pressure or force of the electrons. That's a good way to put it in layman's terms. You also need to remember that voltage is simply a potential, with a "direction" that is relative. Technically, the voltage has no direction at all. In many circuits, voltage is measured relative to ground.

Current, in layman's terms, is sort of the amount of electron flow. If you think of a water pipe, you can think of the pump as a voltage source, and determines how "hard" the water is pushed through the pipe. The current can be compared to the amount of water in the pipe.

Current flows from negative to positive. Electrons have a negative charge, so, in a battery, they are repelled from the (-) and attracted towards the (+). This is where people get confused. Conventional current flow says that current flows from positive to negative, but in reality, that's more of a description of the voltage "direction". Current does not flow (+) to (-), but if ground is assumed to be (-), then the voltage is (+).

I realize that is a little confusing, so I'm just going to rephrase it simply by telling you to ignore conventional current flow. If you understand voltage potential, then that's all you need to know about (+) and (-). Current flows (-) to (+), and if you ever forget that, just remember that electrons have a negative charge. Then you'll be able to remember that the negative side of a battery repels them, and you'll have the direction. Simple.

I hope this helps.
Regards,
Der Strom
 
DerStrom8,

I hate to be picky about this, but some of your statement are just plain wrong.

You are basically correct when you say that Voltage is the pressure or force of the electrons.

Absolutely wrong. Pressure is force/unit area. You have never heard of voltage measured in newtons/meter^2 or pascals, have you?

That's a good way to put it in layman's terms.

No wonder laymen are confused.

You also need to remember that voltage is simply a potential, with a "direction" that is relative. Technically, the voltage has no direction at all. In many circuits, voltage is measured relative to ground.

A potential of what? Isn't every direction relative? Voltage does not move. The energy density of the charge carriers (voltage) increases/decreases at different points in space, but that is not movement. In other words, density does not move. Charges and energy can move.

Current, in layman's terms, is sort of the amount of electron flow.

Rate, or amount of charge carrier movement/unit time would be a better definition for current.

The current can be compared to the amount of water in the pipe.

No, a long pipe of the same diameter as a short pipe has more water in it than the short pipe does, yet the short pipe can have the same flow rate.

Current flows from negative to positive.

Only if the charge carriers are negative. In other materials other than metals, like ions in electrochemistry or PNP semiconductors, the charge carriers are positive and charge flows from positive to negative.

This is where people get confused. Conventional current flow says that current flows from positive to negative, but in reality, that's more of a description of the voltage "direction". Current does not flow (+) to (-), but if ground is assumed to be (-), then the voltage is (+).

The conventional current/voltage concept is a mathematical artifice, not a physical description. Folks seem to have a hard time realizing that. The method does not get bogged down with what direction a particular carrier of a specific polarity moves. Real current does exist from positive to negative if the charge carrier is positive. But that is irrelevant to the conventional current method.

I realize that is a little confusing, so I'm just going to rephrase it simply by telling you to ignore conventional current flow .

Confusing only because of imprecise terms and too many analogies taken too far. I submit that the conventional method is the correct way to go. Otherwise you ignore the way manufacturers mark their semiconductors, and your physical measurement of current with a ammeter will be in an opposite direction from your calculations. You will also find it confusing in circuits where both positive and negative charge carriers exist (like electrochemistry).

 
Hi Nick,


Well, there are simple ways to look at current and voltage that do not require creating any analogies to other things in life. Current and voltage are different than anything else so we end up making analogies to things we already know about so that we can gain some insight, but we can keep the analogies simple and without explaining exactly what is happening and still get insight into how to deal with current and voltage.

First, whenever we have a circuit of some type it is made up of circuit elements. We care what is happening to these circuit elements.

The simple explanation of current and voltage void of and unreal analogies of any type is as follows...

Current is a "Through" variable.
Voltage is an "Across" variable.

In other words:
For current: "It is as if something was existing THROUGH the circuit element".
For voltage: "It is as if something was existing ACROSS the circuit element".

Referring to the diagrams attached:
(A) We usually show a current with a little arrow head inside the lead to the circuit element.
(B) We usually show a voltage either with a long arrow drawn across the element or by using polarity signs.
(C) A current shown to be 5 amps.
(D) Voltages shown to be 5 volts.

The thing to note here is that we never had to refer to any water or anything like that yet we are able to completely describe currents and voltages for those circuit elements.

Someone from another distant far off world might come here and rather than say:
"Oh ok so current in a wire is like water through a pipe".

and instead say:
"Oh yeah ok, so water flowing through a pipe is like current flowing through a wire".

In other words, they never knew what water flowing through a pipe was but they did know what current in a wire was, so they used current in a wire to explain water flow in a pipe rather than the other way around because they take it for granted that something called current flows through a wire, but they are just now learning what water flow through a pipe is.
 
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Absolutely wrong. Pressure is force/unit area. You have never heard of voltage measured in newtons/meter^2 or pascals, have you?

Yes, that is correct. This was only to give the OP a visual idea of the difference between voltage and current. I wasn't saying it's physically what voltage is.


No wonder laymen are confused.

Haha, I agree with that. :D Laymen's terms are far from being able to describe how it actually works. Again, I only use them to give a visual representation of what it might look like, not what it actually is.


A potential of what? Isn't every direction relative? Voltage does not move. The energy density of the charge carriers (voltage) increases/decreases at different points in space, but that is not movement. In other words, density does not move. Charges and energy can move.

Voltage is a potential. That's just what it is. It has the potential to create current flow, and hence the transfer of energy, which leads to work being done. A potential difference is what allows current to flow.

Rate, or amount of charge carrier movement/unit time would be a better definition for current.

Again, laymen's terms. Time is an ever-changing variable which will always be there. Rate is amount/time. Therefore, just saying "amount" infers that it is over time, which is the Rate you speak of.

No, a long pipe of the same diameter as a short pipe has more water in it than the short pipe does, yet the short pipe can have the same flow rate.

Simply an analogy. Not all analogies can be spot-on.

Only if the charge carriers are negative. In other materials other than metals, like ions in electrochemistry or PNP semiconductors, the charge carriers are positive and charge flows from positive to negative.

In standard, simple circuits, the charge carriers are negatively charged (electrons). This statement was assuming the OP isn't working with PNP transistors or anything too complex in theory yet.

The conventional current/voltage concept is a mathematical artifice, not a physical description. Folks seem to have a hard time realizing that. The method does not get bogged down with what direction a particular carrier of a specific polarity moves. Real current does exist from positive to negative if the charge carrier is positive. But that is irrelevant to the conventional current method.

I agree with that. That is what I was saying in that quote. Yes, real current exists from positive to negative if the carrier is positive, but in simple circuits, it is not.

Confusing only because of imprecise terms and too many analogies taken too far. I submit that the conventional method is the correct way to go. Otherwise you ignore the way manufacturers mark their semiconductors, and your physical measurement of current with a ammeter will be in an opposite direction from your calculations. You will also find it confusing in circuits where both positive and negative charge carriers exist (like electrochemistry).

I agree that there are a LOT of analogies here, and that they are not completely perfect. They will not explain everything that's going on--only the parts in question. I don't mean this to be rude, but I think you might be the one who is taking the analogy too far. You're trying to apply it to the big picture, which won't work. You can only apply it to the part for which it was made.
The manufacturers' labels do not usually apply to current direction, rather to voltage potential. You would need to know how the devices work in order to make the proper calculations. It has nothing to do with conventional current flow. If you try using conventional current flow to a real life circuit without taking into account how the devices, or the whole circuit, actually work/s, it will be dead wrong. If you use it, you need to know how the devices work so that you can compensate, but some beginners haven't learned to do that yet.

Regards
 
Hi River :)

Now you see why i suggested abandoning the analogies and going with theory without physical reality and so save the advanced physics for later study. This provides an operational approach that allows one to understand the forest without understanding each individual tree. We can analyze tons of circuits with extraordinary accuracy without ever knowing what current 'flow' is or what really makes up a voltage.
 
DerStrom8,

Yes, real current exists from positive to negative if the carrier is positive, but in simple circuits, it is not.

A battery is a simple electrochemical device that utilizes positive charge carriers.

The manufacturers' labels do not usually apply to current direction, rather to voltage potential. You would need to know how the devices work in order to make the proper calculations.

The arrows on a diode and the arrows on a PNP and NPN schematic are for the conventional representation of current/voltage. You can use a voltmeter and ammeter to prove that no matter how much/little you know about the device.

Ratch
 
Now you see why i suggested abandoning the analogies and going with theory without physical reality and so save the advanced physics for later study. This provides an operational approach that allows one to understand the forest without understanding each individual tree. We can analyze tons of circuits with extraordinary accuracy without ever knowing what current 'flow' is or what really makes up a voltage.

It should at the very least be mentioned in passing while attempting to describe functional electronics the basic physics involved, it's not excessively complex to cover the basic physics in passing and it will give curious learners avenues of further self study. Many commonly accepted teaching methods for electronics attempt too strongly in my opinion to shield the user from the true complexities by using analogies that simply don't hold water (like the water ones) which is probably one of the worst analogies I've run across. Electricity is not like water in a pipe on any level. The water in a pipe in this case is metal, what's moving is energy like a wave through the conductor transferring energy the electrons just carry it.

Take the example of an AC circuit, although electrons are transferring energy from one point to another the electrons themselves don't actually go anywhere. In DC circuits you can calculate how long it would truly take an electron to traverse one end of a copper wire to the other but in most cases this is actually an incredibly long period of time.

The Wikipedia entry for electron drift velocity shows an example calculation of a 3amp current flowing through a 1mm wire results in the electrons taking 1hour to traverse a distance of 1 meter. A surprisingly large bulk of electronic hobbyists don't realize this.
 
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DerStrom8, A battery is a simple electrochemical device that utilizes positive charge carriers.

No. A battery is a perfect example of an electrochemical device that utilizes negative charge carriers. A battery is made up of two main parts--an oxidizer and an electrolyte. The electrolyte causes the oxidizer element to oxidize (give off electrons), which are negative charge carriers. They are then "pushed out" of the negative side of the battery and attracted to the positive side through the circuit.

https://electronics.howstuffworks.com/everyday-tech/battery3.htm
https://www.qrg.northwestern.edu/projects/vss/docs/power/2-how-do-batteries-work.html
 
Lets not get into talking about batteries... they're probably the worst possible example you could give for a 'simple electrochemical device' they're incredibly complex when you get into the reality of how they function. DerStrom gave the short answer.
 
Voltage is the potential to do work.

If you hold a brick above your head, it has the potential to do work (gravitional potential).

If you drop it on your foot, it will do work, ie. crush it.

Current is considered to be a flow of charge carriers such as electrons, positrons, protons, + ions, - ions, holes in semiconductors, etc.

Conventional current flow is considered to be from positive to negative.

This is true for positive charge carriers but negative ones flow in the other direction.

However, the direction of flow of the carriers is usually not important.

When analysing electric circuits, it is easier in the maths to assume conventional flow than electron flow.
 
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The Wikipedia entry for electron drift velocity shows an example calculation of a 3amp current flowing through a 1mm wire results in the electrons taking 1hour to traverse a distance of 1 meter. A surprisingly large bulk of electronic hobbyists don't realize this.

That is why the Hall Effect is just about completely useless in metals. The Hall Effect was discovered 140 years ago, but wasn't used until semiconductors were used as the sensing element, where there are so many fewer charge carriers, so they move much faster and the voltage generated is much more. It also helps that amplifiers can be built into the same piece of silicon as the sensing element.
 
It should at the very least be mentioned in passing while attempting to describe functional electronics the basic physics involved, it's not excessively complex to cover the basic physics in passing and it will give curious learners avenues of further self study. Many commonly accepted teaching methods for electronics attempt too strongly in my opinion to shield the user from the true complexities by using analogies that simply don't hold water (like the water ones) which is probably one of the worst analogies I've run across. Electricity is not like water in a pipe on any level. The water in a pipe in this case is metal, what's moving is energy like a wave through the conductor transferring energy the electrons just carry it.

Take the example of an AC circuit, although electrons are transferring energy from one point to another the electrons themselves don't actually go anywhere. In DC circuits you can calculate how long it would truly take an electron to traverse one end of a copper wire to the other but in most cases this is actually an incredibly long period of time.

The Wikipedia entry for electron drift velocity shows an example calculation of a 3amp current flowing through a 1mm wire results in the electrons taking 1hour to traverse a distance of 1 meter. A surprisingly large bulk of electronic hobbyists don't realize this.

Hi Scead,

It's a good point you made about mentioning some things about the true nature of electricity, i wont say that it is not because it is a good point. Some people get really hung up about this though, and the point i was really trying to make was that it's better to move on with accepted practices rather than try to explain in detail what is going on. It's very hard to explain these things, and it doesnt help as much as we would like to believe. For your example (which was a good one BTW) we have few hobbyists who know how fast charges travel down a wire. But we have zero hobbyists who need to use this information for any practical project they are building. If they take the time to learn circuit analysis really well, they can understand a huge range of circuits. If they get hung up on trying to understand the very nature of electricity they have to get into much more advanced principles and mathematics, which they are not usually prepared to do.

But as i said i do agree that some mention is worth it :)
 
DerStrom8,

No. A battery is a perfect example of an electrochemical device that utilizes negative charge carriers. A battery is made up of two main parts--an oxidizer and an electrolyte. The electrolyte causes the oxidizer element to oxidize (give off electrons), which are negative charge carriers. They are then "pushed out" of the negative side of the battery and attracted to the positive side through the circuit.

That is all correct as far as the external current goes. But, the +ions that give up their electron for external current have to go to the cathode where they receive a returning electron and get neutralized. That path is within the battery, and is an example of a positive charge moving. This has to happen, otherwise the anode would clog up with +ions and the cathode would clog up with electrons. Therefore an internal current of positive charges exists within the battery to neutralize the internal charge build up. This positive charge internal current has to equal the external negative charge current.

Ratch
 
ljcox,

Voltage is the potential to do work.

No, because then it would have units of joules (MKS) instead of joules/coulomb. Voltage is a density, not a unit of electrical potential energy.

If you hold a brick above your head, it has the potential to do work (gravitional potential).

Because of its potential energy, measured in joules (MKS).

Current is considered to be a flow of charge carriers such as electrons, positrons, protons, + ions, - ions, holes in semiconductors, etc.

Qualitatively yes, but a quantitive definition requires a per unit of time also.

Conventional current flow is considered to be from positive to negative.

Mathematically assumed to be positive to negative charge movement of a voltage source.

However, the direction of flow of the carriers is usually not important.

For calculations, unually not. But the assumptions of conventional current/voltage must be adhered to.

This is true for positive charge carriers but negative ones flow in the other direction.

Yes, negative charge carriers are assumed to flow in the opposite direction of positive charge carriers.

When analysing electric circuits, it is easier in the maths to assume conventional flow than electron flow.

Yes, then you have only one current direction to worry about.

Ratch
 
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