This how I think of voltage / resistance / current

[vulturebetrayer]

Hello everyone.

I wrote the following up last night.  It's how I would explain the relationship between voltage, resistance and current.  Note, I am using Intensity of Current when discussing this because I feel it's important to hammer home the relationship between the variables in Ohms equations. 

Understanding the relationship of variables has been of the major issues I have run into when attempting to learn electronics equations.

I am concerned that maybe I'm missing something.  Maybe, I'm totally wrong and need a huge correction. 

I'd like to share this on my site with some examples and decent anecdotes that give real world problems new electronics folks may run into when attempting their first projects.  One example I can think of is using a resistor to limit current so as not to blow an LED;  maybe changing voltages using a buck converter or voltage regulator.

So all this started out as notes and then I added some structure to explain this to myself.
This is how I learn, by writing everything out and then going over it meticulously and finally showing someone who knows their stuff and having them explain to me where I'm horribly wrong.

So please take a look at this info and tell me what you would like changed / added / corrected:


V is Voltage measured in Volts
I is Intensity of current measured in Amps
R is Resistance measured in Ohms

•   Ohms Law:

•   Volts = Intensity times Resistance
•   V=IR

•   Intensity = Volts divided by Resistance
•   I = V/R

•   Resistance = Volts divided by Intensity
•   R = V/I

Practical Nomenclature of Ohms Law:
•   Volts Amps Ohms
•   Volts = Amps times Ohms
•   Ohms = Volts divided by Amps
•   Amps = Volts divided by Resistance

Think of voltage like like the 'speed' of electricity.  It's the difference in electrical potential.  This basically is the path the electrons you are pushing are going to follow.  Think of it as a moving pathway the electrons hitch a ride on, the more Volts the faster the electrons move.

Think of Amps like the intensity of the electricity or the amount of electrons being pushed at a time.  Think of the electrons on the moving pathway (Voltage) piling on more and more, you can move more electrons at a time if there are more amps.

Think of Ohms as amperage absorption.  The circuit uses a certain amount of amps to be functional, yet sometimes it is important to limit the amount of ohms.

So you must supply the proper voltage and amperage.  Your circuit may contain components that are not self-limiting in amperage; meaning it may want to pull more amps than it can handle, (which is a wonderful way to release magic smoke).  This is why you will need to calculate resistance and add a resistor if necessary to the positive side of the component if necessary.


After this I'd like to add some circuit examples, and real life equations.

I haven't considered explaining rectification because I don't fully understand the equations involved in the calculations.  I have built a rectifier using diodes, but don't understand how I'd choose different components other than using a generic schematic (still trying to wrap my brain around 'flutter' too with caps), so any resources on rectifiers and capacitance and flutter, and I'd be very thankful!

Thanks in advance!

[IanB]

So please take a look at this info and tell me what you would like changed / added / corrected:


V is Voltage measured in Volts
I is Intensity of current measured in Amps
R is Resistance measured in Ohms

•   Ohms Law:

•   Voltage = Intensity times Resistance
•   V=IR

•   Intensity = Voltage divided by Resistance
•   I = V/R

•   Resistance = Voltage divided by Intensity
•   R = V/I

Voltage is the quantity, volts is the unit of measure. If you are writing Intensity and Resistance, then you should write Voltage for consistency.

Practical Nomenclature of Ohms Law:
•   Volts Amps Ohms
•   Volts = Amps times Ohms
•   Ohms = Volts divided by Amps
•   Amps = Volts divided by ResistanceOhms

Think of voltage like like the 'speed' of electricity.  It's the difference in electrical potential.  This basically is the path the electrons you are pushing are going to follow.  Think of it as a moving pathway the electrons hitch a ride on, the more Volts the faster the electrons move.

Not quite. Voltage is like the 'pressure' of the electricity. It is how hard it pushes. If there are more volts the electricity will try harder to break through an obstacle and more current will flow.

Think of Amps like the intensity of the electricity or the amount of electrons being pushed at a time.  Think of the electrons on the moving pathway (Voltage) piling on more and more, you can move more electrons at a time if there are more amps.

Think of Ohms as amperage absorption.  The circuit uses a certain amount of amps to be functional, yet sometimes it is important to limit the amount of ohms.

No, current is never absorbed. Current is always conserved and never disappears. This is a very important law of electricity.

So you must supply the proper voltage and amperage.  Your circuit may contain components that are not self-limiting in amperage; meaning it may want to pull more amps than it can handle, (which is a wonderful way to release magic smoke).  This is why you will need to calculate resistance and add a resistor if necessary to the positive side of the component if necessary.

[edy]

I would alter this conceptualization quite a bit. For example, voltage is not the "speed" of the electricity nor the path it wants to push or follow. Ohms is not amperage absorption, and the idea of what Amps are is a bit hard to follow. While I appreciate your explanation, and it seems you did a lot of thinking about it, I want to clarify it based on my experience and what may be easier to teach people.

VOLTAGE:

Voltage is the difference in potential energy between two points. Just like gravitational field creates different potential at different heights above the ground. What happens is when there is a difference in energy levels, a FORCE is created that tries to equalize the difference (make it zero). For people jumping off buildings, the potential difference in gravitational energy turns into MOTION and you fall, picking up speed until you hit the ground. For electrons, the difference in potential energy causes EMF or electromotive force which moves electrons.

Now, if you are using the water analogy, you can also think of voltage as say the height of a waterfall. You can have a very tall waterfall, or a short waterfall. The taller waterfall is like higher amount of voltage. Obviously the water analogy only goes so far... it is an analogy. But essentially when you have a battery, or a capacitor, or static electricity building up between 2 objects.... There is a separation of CHARGES which creates a voltage or potential energy difference between 2 points in space. At some point, whether you have a conductor between these points or not, if the voltage difference will get big enough it will want to jump across the path.

In the case of a battery, if you connect the 2 ends with a wire (conductive path) the electrons will flow quite easily from one side to the other. Now, if you have static electricity you will need very large voltages to build up before a spark is created across the gap... because air is a poor conductor.

So in summary, voltage is when you have a CHARGE DIFFERENCE across something. That's all. How you choose to connect things across the charge difference (what materials, objects, etc.) will result in properties that you can measure called AMPERAGE (the number of electrons passing by per second) and RESISTANCE (an intrinsic property of the material to allow electrons to pass through it).


RESISTANCE:

Materials have the ability to allow electrons to flow through easily (conductor) or more difficult (insulator). Metals typically are better conductors because of the presence of "free" electrons, so they are not as tightly bound to the atoms and can move around through the metal, exchanging places with the ones beside them, so that the metal overall remains the same but yet there is the ability for electrons being supplied on one side of the metal able to make their way to the other side. That's what happens in a wire.

When you have an insulator, the electrons cannot pass through easily. They are more tightly bound to their atoms. So in order to make the electrons flow, you will need a HIGHER VOLTAGE. The bigger the potential difference between the 2 sides of the insulator (or the thinner the insulator) at some point electrons will flow. But not many.... that's when AMPERAGE comes in, because Voltage, Amps and Resistance are all related by Ohm's law.

AMPERAGE:

So now imagine you have a VOLTAGE being applied across a material with a certain intrinsic property called RESISTANCE. The voltage creates a potential energy difference across the material, so electrons wish to move across the material. There is a force generated, wishing to move the electrons across. That force causes movement of the electrons but has nothing to do with the speed of the electrons, because if you have a large resistance, those electrons may still move with much difficulty through the material, if any move at all.

The amperage is the net amount of electrons moving per second across the wire, or the net amount of charge in Coulombs. Given the same amount of resistance in a wire, if you increase voltage across it by 10x, you will get 10x increase in the net number of electrons travelling across the wire as well. So in general, the more voltage you apply to something, the more amps will flow across it.

Using the water analogy, if you think of a water pipe..... If the resistance is the size of the pipe (diameter), then voltage is the pressure being applied to the water to move, and the amperage is how much water is flowing through the pipe per second. So imagine a very tiny pipe (high resistance), you apply pressure to one end. Call that pressure P (this is like the voltage). Now you measure the number of gallons flowing through the pipe past a certain point.... that's like your amperage.

Now imagine you increase the diameter of your pipe, make it 2x wider. You need less pressure to push the water through... less voltage is needed to get the same amount of flow! So if your resistance drops to 1/2, keeping same voltage (pressure), you increase amps 2x (more current). Now imagine you have the same pipe but all you do is increase pressure by 2x, then your flow rate or amperage will also increase by 2x.

Anyways, I hope this makes more sense.... Electricity is not always as intuitive, and we can't use macroscopic analogies to always understand microscopic atomic/quantum phenomenon. But this is a good start.

 

[WaveyDipole]

Think of voltage like like the 'speed' of electricity.  It's the difference in electrical potential.  This basically is the path the electrons you are pushing are going to follow.  Think of it as a moving pathway the electrons hitch a ride on, the more Volts the faster the electrons move.

Voltage is 'the difference in electrical potential' but it would be incorrect to relate it to the 'speed' of electricity. The speed of electricity is related to the dielectric constant of the medium that it travels in. In a vacuum, electricity travels at the speed of light, which is about 300,000 kilometers per second. This is not related to the voltage, so it is incorrect to say that the more Volts the faster the electrons move. Voltage is a measure of potential difference, or electrical tension or pressure. Think of it like water pressure. The greater the pressure, the greater the POTENTIAL there is to release a greater or more powerful flow of water.

Think of Amps like the intensity of the electricity or the amount of electrons being pushed at a time.  Think of the electrons on the moving pathway (Voltage) piling on more and more, you can move more electrons at a time if there are more amps.

The flow of electricity is referred to as 'current' and amps are a measure of the intensity of that current flow. The greater the flow, the greater its measurement in amps. This is related to potential (the Volt is a measure of potential) because the greater the potential, the greater current will flow. For example, the higher the water pressure, the greater the volume of water that will flow in the same time frame when the tap is opened.

Think of Ohms as amperage absorption.  The circuit uses a certain amount of amps to be functional, yet sometimes it is important to limit the amount of ohms.

Ohms is a measure of resistance. The greater the resistance the more your current flow is impeded. Its a bit like the tap - the tighter it is closed, the higher the resistance to the water flow and therefore less water flows.  In electrical circuits, resistance restricts current flow and will often cause some energy to be given off as heat. While a circuit is working it consumes a certain amount of POWER which is measured in Watts and is a function of amps times volts (W = VA). I guess you could characterize this rather loosely as 'amperage absorption' as while current is flowing the circuit is carrying out work and consuming power. Current itself is not absorbed, just like water flowing through the pipe - it isn't absorbed anywhere as it has nowhere to go, except when it leaves the tap at which point it is expended.

So you must supply the proper voltage and amperage.  Your circuit may contain components that are not self-limiting in amperage; meaning it may want to pull more amps than it can handle, (which is a wonderful way to release magic smoke).  This is why you will need to calculate resistance and add a resistor if necessary to the positive side of the component if necessary.
[/tt][/b]

While it is true that in order to energize a circuit you need to supply the 'voltage' or electrical potential (e.g. a battery or AC power), 'amperage' is a measure of current flow, which is what happens when you activate the circuit by throwing the 'On' switch. You don't exactly supply it. Its a bit like opening a tap. The water is under pressure and is released and starts to flow. You can regulate the flow depending on how wide you open the tap. In a similar way, electricity starts to flow around your circuit. So with your example with the resistor and LED, you calculate the resistor such that sufficient current flows to light the LED but not burn it out. Its not so much that you supply the amps, but that you design the circuit to regulate the current flow, which in the case of a LED will be measured in milliamps.

No component is 'self-limiting in amperage'. It will have certain design characteristics which mean it will have minimum requirements in order to work satisfactorily and specified maximum limits that must not be exceeded otherwise the component will suffer damage - and possibly release 'magic smoke' in the process. So yes, one calculates the circuit design in order to avoid that.

PS. A couple of replies came in while I was typing this so apologies for any duplication.

[Ratch]

Hello everyone.

I wrote the following up last night.  It's how I would explain the relationship between voltage, resistance and current.  Note, I am using Intensity of Current when discussing this because I feel it's important to hammer home the relationship between the variables in Ohms equations. 

Understanding the relationship of variables has been of the major issues I have run into when attempting to learn electronics equations.

I am concerned that maybe I'm missing something.  Maybe, I'm totally wrong and need a huge correction. 

I'd like to share this on my site with some examples and decent anecdotes that give real world problems new electronics folks may run into when attempting their first projects.  One example I can think of is using a resistor to limit current so as not to blow an LED;  maybe changing voltages using a buck converter or voltage regulator.

So all this started out as notes and then I added some structure to explain this to myself.
This is how I learn, by writing everything out and then going over it meticulously and finally showing someone who knows their stuff and having them explain to me where I'm horribly wrong.

So please take a look at this info and tell me what you would like changed / added / corrected:

Yes, you need lots of correction.

V is Voltage measured in Volts
I is Intensity of current measured in Amps
R is Resistance measured in Ohms

You don't define quantities by reciting their measurement units.  Volts is not defined by voltage, amps is not defined by amperage, and resistance is not defined by ohms (notice that when used as a unit, "ohm" is not capitalized). 

•   Ohms Law:

•   Volts = Intensity times Resistance
•   V=IR

•   Intensity = Volts divided by Resistance
•   I = V/R

•   Resistance = Volts divided by Intensity
•   R = V/I

Practical Nomenclature of Ohms Law:
•   Volts Amps Ohms
•   Volts = Amps times Ohms
•   Ohms = Volts divided by Amps
•   Amps = Volts divided by Resistance

The good and correct physics books will tell you that Ohm's law is not V=IR and all its variations. Ohm's law refers to a material's electrical linearity property.  If a material, like most metals, conducts current in direct proportion to the voltage applied across it, it is considered "ohmic" and follows Ohm's law.  Materials, such as gases or components such as junction diodes, have very nonlinear voltage vs current curves, and do not follow Ohm's law.  V=IR and its variations is very correct, because it is the definition of resistance.  Again, it is not Ohm's law.  This misnomer has been propagated in many textbooks and other technical literature.  V=IR should be referred to correctly as the definition of resistance, and Ohm's law as a property of a material.

Think of voltage like like the 'speed' of electricity.

What is the speed of "electricity"?  Anyway, voltage is not a speed measurement.

It's the difference in electrical potential.

The potential of what?

This basically is the path the electrons you are pushing are going to follow.  Think of it as a moving pathway the electrons hitch a ride on, the more Volts the faster the electrons move.

Charge carriers (electrons in metals) follow a conduction path, not the voltage.  Units of "volts" are not capitalized.

Think of Amps like the intensity of the electricity or the amount of electrons being pushed at a time.  Think of the electrons on the moving pathway (Voltage) piling on more and more, you can move more electrons at a time if there are more amps.

Amps, like volts is not capitalized.  "Intensity" in physics means a quantity of something per unit.  A better word for the amount of amps is "value".  Amps is the charge flow per unit time.  "Electricity" of a vague term that can mean almost anything pertaining to electrical science.

Think of Ohms as amperage absorption.  The circuit uses a certain amount of amps to be functional, yet sometimes it is important to limit the amount of ohms.

Ouch!  That explanation hurts.

Resistance does not "absorb" amperage.  Resistance is an impediment to charge carrier flow.  Voltage is the energy density of electrical energy per unit charge.  That is why voltage has MKS units of joules/coulomb.  Look at it this way.  It takes energy to bring two electrons together, because they want to repel each other.  It takes more energy to bring many electrons together.  It takes still more energy to bring all the electrons closer together.  If you have a higher energy per unit of electrons (voltage) at one end of a wire, the electrons are going to move to the other end of the wire where the energy per unit of electrons (voltage) is lower.  This is because they naturally want to spread away from each other, so they go from high energy density per unit to the lower voltage.  During their trip through the wire they encounter resistance which causes them to lose energy as heat.  Therefore, they arrive at the lower voltage end of the wire with less energy density per unit charge (voltage).

So you must supply the proper voltage and amperage.  Your circuit may contain components that are not self-limiting in amperage; meaning it may want to pull more amps than it can handle, (which is a wonderful way to release magic smoke).  This is why you will need to calculate resistance and add a resistor if necessary to the positive side of the component if necessary.
[/tt][/b]

After this I'd like to add some circuit examples, and real life equations.

I haven't considered explaining rectification because I don't fully understand the equations involved in the calculations.  I have built a rectifier using diodes, but don't understand how I'd choose different components other than using a generic schematic (still trying to wrap my brain around 'flutter' too with caps), so any resources on rectifiers and capacitance and flutter, and I'd be very thankful!

Thanks in advance!

Ratch

[Stephan_T]

Hi,
just as brief thoughts about the basic electric terms:

CURRENT is what flows. The flow (transfer) of electric charge.

RESISTANCE is the property of an electric conductor, which hinders the current flow.

VOLTAGE, I find a bit more difficult to explain.

I would like to encourage you to look at other languages. The French term for voltage is "tension électrique".
In German it is called "elektrische Spannung". Looking at other english translations for this German word you find "electric tension", but also concepts like:
strain (on rope), pressure, eagerness, etc.
see http://dict.leo.org/?search=Spannung

So VOLTAGE is more of an electric push/pull kind of idea. I think of it as the electric tension that may cause a current to flow, as long as there is some kind of conductor available.

My most important thought about Ohms law is to remember that it only applies to conductors. You may have heard of "isolation resistance", but that is following Ohms law.

I remember Ohms law always in the form

R = V / I
where R is constant, while V and I may be turned up or down.

The basic idea is to observe the relation (ratio) between voltage and current at a given (passive) conductive component.
[while I was writing this, Ratch has given the better explanation of Ohms law]
The number of Ohms is the basically the number of volts that it takes to push one ampere through the resistor. Especially when looking at small resistance values (for example contact resistance of plugs and switches), I am using a 1A constant current source and measure the voltage drop across the resistor/resistance. The mV values directly translate to mOhms.

Included here is another important concept: The voltage drop. When current flows through a resistor/resistance, we speak of the voltage drop. In fact, I think of every voltage measurement actually as a measurement of the current through the (high) internal resistance of the meter.

[onlooker]

With all the more precise definitions and explanations, I expect the OP would get more confused. Based on the OP's writing, I think the better intuitive description or correction is to use the  analogy of water pipe network.
Nothing precise here, but can relates to other daily experience better.

Voltage     = pressure difference between any two points in the pipe network.
Current     = water flow (per second water volume flowing through a cross-section of a pipe)
Resistance = pipe resistance (e.g. thin or long pipe tends to restrict/slow down water flow more)
Battery     = water pump (to create pressure difference in the pipe network)
Capacitor   = Water tank with flexible membrane separate the inlet/outlet of the tank into 2 halves.
Inductor    =  water inertia (that create water hammers) 
Diode        = check valve/one-way valve.
...

[amyk]

Hi,
just as brief thoughts about the basic electric terms:

CURRENT is what flows. The flow (transfer) of electric charge.

RESISTANCE is the property of an electric conductor, which hinders the current flow.

VOLTAGE, I find a bit more difficult to explain.

I would like to encourage you to look at other languages. The French term for voltage is "tension électrique".
In German it is called "elektrische Spannung". Looking at other english translations for this German word you find "electric tension", but also concepts like:
strain (on rope), pressure, eagerness, etc.
see http://dict.leo.org/?search=Spannung

So VOLTAGE is more of an electric push/pull kind of idea. I think of it as the electric tension that may cause a current to flow, as long as there is some kind of conductor available.

It's interesting that you bring up the other languages, because in Chinese, the words for voltage is literally "electron pressure", current is "electron flow", and resistance is something like "electron obstruct".

In English, "current" should be interpreted not as in "new", but as in the movement of water in a river. The water analogy is probably the most intuitive and closest approximation to understanding; and it's been around for over 100 years, so you would be unlikely to find a better analogy.

[Ratch]

Hi,
just as brief thoughts about the basic electric terms:

CURRENT is what flows.

No, the charge carriers are what flow.  Current is the amount of charge carriers per unit time.

The flow (transfer) of electric charge.

Only means movement unless a rate is specified.

RESISTANCE is the property of an electric conductor, which hinders the current flow.

No, resistivity is a property of a material (electrical conductor).  Resistance is determined by the resistivity and the shape of the material.

VOLTAGE, I find a bit more difficult to explain.

I already did in my previous post.

I would like to encourage you to look at other languages. The French term for voltage is "tension électrique".
In German it is called "elektrische Spannung". Looking at other english translations for this German word you find "electric tension", but also concepts like:
strain (on rope), pressure, eagerness, etc.
see http://dict.leo.org/?search=Spannung

So VOLTAGE is more of an electric push/pull kind of idea. I think of it as the electric tension that may cause a current to flow, as long as there is some kind of conductor available.

If they don't describe voltage as the energy density per unit charge, then they are misdefining voltage.  The MKS units of voltage are joules/coulomb.  Current does not flow, by the way.  Charge flow rate is current.  Current flow means charge flow rate flow, which is redundant and ridiculous.  Current should be described as being present or existing.

My most important thought about Ohms law is to remember that it only applies to conductors. You may have heard of "isolation resistance", but that is following Ohms law.

Yes, you have to have conduction before you can determine whether the conduction is linear or not.

I remember Ohms law always in the form

R = V / I
where R is constant, while V and I may be turned up or down.

That is a false definition for Ohm's law.  That is the definition of resistance.  Ohm's law pertains to electrical linearity.

The basic idea is to observe the relation (ratio) between voltage and current at a given (passive) conductive component.
[while I was writing this, Ratch has given the better explanation of Ohms law]
The number of Ohms is the basically the number of volts that it takes to push one ampere through the resistor. Especially when looking at small resistance values (for example contact resistance of plugs and switches), I am using a 1A constant current source and measure the voltage drop across the resistor/resistance. The mV values directly translate to mOhms.

I specifically said that V=IR was not Ohm's law, but instead the definition of resistance.

Included here is another important concept: The voltage drop. When current flows through a resistor/resistance, we speak of the voltage drop. In fact, I think of every voltage measurement actually as a measurement of the current through the (high) internal resistance of the meter.

Which is an application of the definition of resistance, not Ohm's law.

Ratch
Hopelessly Pedantic

[Ratch]

With all the more precise definitions and explanations, I expect the OP would get more confused. Based on the OP's writing, I think the better intuitive description or correction is to use the  analogy of water pipe network.
Nothing precise here, but can relates to other daily experience better.

Does the analog water pipe circuit leak?

Voltage     = pressure difference between any two points in the pipe network.
Current     = water flow (per second water volume flowing through a cross-section of a pipe)
Resistance = pipe resistance (e.g. thin or long pipe tends to restrict/slow down water flow more)
Battery     = water pump (to create pressure difference in the pipe network)
Capacitor   = Water tank with flexible membrane separate the inlet/outlet of the tank into 2 halves.
Inductor    =  water inertia (that create water hammers) 
Diode        = check valve/one-way valve.
...

Will you get wet?

Ratch
Hopelessly Pedantic

[BobsURuncle]

Quote from: vulturebetrayer on Yesterday at 06:19:12 PM

Hello everyone.

I wrote the following up last night.  It's how I would explain the relationship between voltage, resistance and current.  Note, I am using Intensity of Current when discussing this because I feel it's important to hammer home the relationship between the variables in Ohms equations. 

>Understanding the relationship of variables has been of the major issues I have run into when attempting to learn electronics equations.

I am concerned that maybe I'm missing something.  Maybe, I'm totally wrong and need a huge correction. 

I'd like to share this on my site with some examples and decent anecdotes that give real world problems new electronics folks may run into when attempting their first projects.  One example I can think of is using a resistor to limit current so as not to blow an LED;  maybe changing voltages using a buck converter or voltage regulator.

So all this started out as notes and then I added some structure to explain this to myself.
This is how I learn, by writing everything out and then going over it meticulously and finally showing someone who knows their stuff and having them explain to me where I'm horribly wrong.

So please take a look at this info and tell me what you would like changed / added / corrected:


V is Voltage measured in Volts
I is Intensity of current measured in Amps
R is Resistance measured in Ohms

•   Ohms Law:

•   Volts = Intensity times Resistance
•   V=IR

•   Intensity = Volts divided by Resistance
•   I = V/R

•   Resistance = Volts divided by Intensity
•   R = V/I

Practical Nomenclature of Ohms Law:
•   Volts Amps Ohms
•   Volts = Amps times Ohms
•   Ohms = Volts divided by Amps
•   Amps = Volts divided by Resistance

Think of voltage like like the 'speed' of electricity.  It's the difference in electrical potential.  This basically is the path the electrons you are pushing are going to follow.  Think of it as a moving pathway the electrons hitch a ride on, the more Volts the faster the electrons move.

Think of Amps like the intensity of the electricity or the amount of electrons being pushed at a time.  Think of the electrons on the moving pathway (Voltage) piling on more and more, you can move more electrons at a time if there are more amps.

Think of Ohms as amperage absorption.  The circuit uses a certain amount of amps to be functional, yet sometimes it is important to limit the amount of ohms.

So you must supply the proper voltage and amperage.  Your circuit may contain components that are not self-limiting in amperage; meaning it may want to pull more amps than it can handle, (which is a wonderful way to release magic smoke).  This is why you will need to calculate resistance and add a resistor if necessary to the positive side of the component if necessary.


After this I'd like to add some circuit examples, and real life equations.

I haven't considered explaining rectification because I don't fully understand the equations involved in the calculations.  I have built a rectifier using diodes, but don't understand how I'd choose different components other than using a generic schematic (still trying to wrap my brain around 'flutter' too with caps), so any resources on rectifiers and capacitance and flutter, and I'd be very thankful!

Thanks in advance!

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

You have a number of conceptual errors here, as do some of the other contributors to this thread.  Watch this video, it will set you down the correct path.

[IanB]

The good and correct physics books will tell you that Ohm's law is not V=IR and all its variations. Ohm's law refers to a material's electrical linearity property.  If a material, like most metals, conducts current in direct proportion to the voltage applied across it, it is considered "ohmic" and follows Ohm's law.  Materials, such as gases or components such as junction diodes, have very nonlinear voltage vs current curves, and do not follow Ohm's law.  V=IR and its variations is very correct, because it is the definition of resistance.  Again, it is not Ohm's law.  This misnomer has been propagated in many textbooks and other technical literature.  V=IR should be referred to correctly as the definition of resistance, and Ohm's law as a property of a material.

If you want to say a material conducts current in direct proportion to the voltage across it, then

   I = (1/R) · V

is a precise mathematical statement of the same thing, where (1/R) is the constant of proportionality. The only difference is that the law of proportionality is in the first instance expressed in words and in the second in mathematical notation. It is the exact same statement either way.

If they don't describe voltage as the energy density per unit charge, then they are misdefining voltage.  The MKS units of voltage are joules/coulomb.

In physics, pressure has dimensions of energy per unit volume, but this is not a commonly useful way to think about pressure. Hence 1 Pa is usually defined as 1 N/m² rather than 1 J/m³.

Similarly, it is much more intuitive to think about voltage as an electrical pressure than as an energy density, especially for people who are trying to grasp fundamentals. There is a place to get into deep philosophical debates, but teaching is not it.

[Ratch]

-----------------------------------------------------

You have a number of conceptual errors here, as do some of the other contributors to this thread.  Watch this video, it will set you down the correct path.

[url=https://www.youtube.com/watch?v=yRLuZg5dm-E]https://www.youtube.com/watch?v=yRLuZg5dm-E

It was humorous seeing a disembodied head and hand doing the talking and gesturing.  I think analogs are OK for illustrating and explaining a particular point, but are confusing when coupled to another physics discipline.   Do hydraulic engineers learn their craft by studying electrical technology?  If not, then why should electrical students study hydraulics?  The professor seemed to imply that positive charges were present in a electrical circuit.  That, of course is not true.  Only negative charges are present in wires. Why do the analog folks equate pressure (force per unit area) with voltage.  I would think they would choose force for voltage.   After all, the electric field does exert a force on the conducting electrons.  The prof equated physical height with voltage, which I thought was not necessary.  Voltage is really an energy density, and is not a difficult concept to understand.

It would be instructive if you pointed out any errors and misconceptions you find in this thread.

Ratch
Hopelessly Pedantic

[Ratch]

The good and correct physics books will tell you that Ohm's law is not V=IR and all its variations. Ohm's law refers to a material's electrical linearity property.  If a material, like most metals, conducts current in direct proportion to the voltage applied across it, it is considered "ohmic" and follows Ohm's law.  Materials, such as gases or components such as junction diodes, have very nonlinear voltage vs current curves, and do not follow Ohm's law.  V=IR and its variations is very correct, because it is the definition of resistance.  Again, it is not Ohm's law.  This misnomer has been propagated in many textbooks and other technical literature.  V=IR should be referred to correctly as the definition of resistance, and Ohm's law as a property of a material.

If you want to say a material conducts current in direct proportion to the voltage across it, then

   I = (1/R) · V

is a precise mathematical statement of the same thing, where (1/R) is the constant of proportionality. The only difference is that the law of proportionality is in the first instance expressed in words and in the second in mathematical notation. It is the exact same statement either way.

I agree with the above statement, but how does that apply to the definition of Ohm's law?

In physics, pressure has dimensions of energy per unit volume, but this is not a commonly useful way to think about pressure. Hence 1 Pa is usually defined as 1 N/m² rather than 1 J/m³.

Nope, those are different units.  I challenge you to show me a link or other proof describing pressure defined that way.

Similarly, it is much more intuitive to think about voltage as an electrical pressure than as an energy density, especially for people who are trying to grasp fundamentals. There is a place to get into deep philosophical debates, but teaching is not it.

Intuitive?  I cannot conceive what "electrical pressure" is.  How would anyone put the definition of basic physical units into a philosophical concept?

Ratch
Hopelessly Pedantic

[IanB]

Ratch
Hopelessly Pedantic

You are messing up your quoting, making it hard to follow your posts.

Initially I thought from your signature that you were being deliberately obtuse. But it seems you genuinely lack understanding.

Rather than point out your mistakes right away, I will leave you some time to review what you have posted and see if you can work them out for yourself.

For now, I'll just state that voltage is indeed the direct electrical analog of hydraulic pressure.

[Ratch]

You are messing up your quoting, making it hard to follow your posts.

I try to eliminate some repetitive material that has been posted before, and break up the posts to answer individual points.  Sorry if some material is missing.

Initially I thought from your signature that you were being deliberately obtuse. But it seems you genuinely lack understanding.

Say on.  I am always ready to defend my positions.

Rather than point out your mistakes right away, I will leave you some time to review what you have posted and see if you can work them out for yourself.

I already have before I posted.  I just looked again and cannot see anything amiss.  Please list the items you don't agree with so I can elucidate my statements.

For now, I'll just state that voltage is indeed the direct electrical analog of hydraulic pressure.

So what if it is?  Like I said before, why study hydraulics instead of electronics?

Ratch
Hopelessly Pedantic

[IanB]

I try to eliminate some repetitive material that has been posted before, and break up the posts to answer individual points.  Sorry if some material is missing.

Please look back at your posts and see what you are doing. You are placing your words inside a quote block as if you are quoting me. This is not cool. Please fix it.

[Ratch]

IanB,

Well, I gave it my best shot.  It looks a little different, but I don't think the clarity of the narrative is much different.

Ratch
Hopelessly Pedantic

[IanB]

Well, I gave it my best shot.  It looks a little different, but I don't think the clarity of the narrative is much different.

Thanks, that makes it clearer who is being quoted 

[IanB]

If you want to say a material conducts current in direct proportion to the voltage across it, then

   I = (1/R) · V

is a precise mathematical statement of the same thing, where (1/R) is the constant of proportionality. The only difference is that the law of proportionality is in the first instance expressed in words and in the second in mathematical notation. It is the exact same statement either way.

I agree with the above statement, but how does that apply to the definition of Ohm's law?

If two statements are equivalent, and one statement is a statement of Ohm's law, then the other statement is also a statement of Ohm's law.

In physics, pressure has dimensions of energy per unit volume, but this is not a commonly useful way to think about pressure. Hence 1 Pa is usually defined as 1 N/m² rather than 1 J/m³.

Nope, those are different units.  I challenge you to show me a link or other proof describing pressure defined that way.

Well, you can work it out: 1 J/m³ = 1 Nm/m³ = 1 N/m². The units are identical. The identity of pressure with energy per unit volume is very important in physics and engineering.

Similarly, it is much more intuitive to think about voltage as an electrical pressure than as an energy density, especially for people who are trying to grasp fundamentals. There is a place to get into deep philosophical debates, but teaching is not it.

Intuitive?  I cannot conceive what "electrical pressure" is.  How would anyone put the definition of basic physical units into a philosophical concept?

When you said voltage was best understood as energy per unit charge I thought you were trying sow confusion, hence my misplaced comment about philosophical debates. Sorry about that.

But "electrical pressure" is nothing but voltage. You will find voltage described as electrical pressure in physics texts.

It works like this. Pressure is energy per unit volume (J/m³) and voltage is energy per unit charge (J/C). Both pressure and voltage are forms of energy density. Both pressure and voltage are also forms of motive force or potential (hence voltage differences are often referred to as EMF--electromotive force, or as PD--potential difference).

Continuing the similarity, if I wish to move a unit volume of fluid across a pressure gradient I have to do work on the fluid proportional to the difference in pressure (and in SI units the work performed is measured in joules). If I wish to move a unit of charge across a voltage gradient I have to do work on the charge proportional to the difference in voltage (and in SI units the work performed is also measured in joules).

Such similarities between potentials and flows in different domains are very useful in physics as an aid to understanding concepts. They are something students should learn to appreciate early in their studies.

[helius]

That was very good; basic, but excellent pedagogy. The professor has obviously had many experiences trying to explain electrical concepts to resistant (lol) students and thinking of better ways to do it. I think it's very easy to forget how we acquired our own basic knowledge and make the assumption that what seems obvious to us should be obvious to others, but finding clear, correct ways to explain our knowledge is not trivial.

The idea that voltage IS height, not a metaphor but literally, is fine if that is how you choose to think of it. You do need to be careful, however, because while a bare statement like that is not an analogy, the mind quickly jumps to analogies when using it. Later in the video the professor says "and if this colomb rolls down from 3V to 0V..." which sneaks across the analogy of rolling. Care is needed because there is no analog of inertia in the electrical world.

The professor seemed to imply that positive charges were present in a electrical circuit.  That, of course is not true.  Only negative charges are present in wires.

It's fine to be pedantic, but don't give that as an excuse for being dead wrong. If only negative charges were present there would be a huge net negative charge. The charge on a 1 square foot double-sided PCB would be -100 kilocoulombs, making it explode instantly at near the speed of light 
(With a relative permittivity of 4.7 across a 1.57mm thick FR-4 substrate, the force pulling on it would be .3 zettanewtons.)

[LvW]

Watch this video, it will set you down the correct path.

Thanks for the great video.
To me, the most important part of the video is mentioning the role of the electric field within the conducting material (wire or resistor or semiconductor).
This makes clear that the existence of a current (movement of charges) within each conducting material requires as a precondition an electric field - that means: An electric voltage!

Hence, from the physical point of view it is not correct (as we very often can hear or read) to say "a current is injected into..." or even "we pump a current into...".
It is always the voltage which allows a current - not vice versa. (And it is not a "chicken/egg problem" as I have heard very often).
I think, these facts are important for a good understanding of the relations between voltage and current.
As another example: In electronics, a so-called "current source" is always a voltage source equipped with a very large internal dynamic source resistance. 

Of course, for analyzing/designing circuits it is common practice to assume that a current can create a voltage V=IR across a resistor (simple example: resistive voltage divider).
But we always should keep in mind that such a mathematical relation does not imply any statement regarding cause and effect.       
(Similar considerations apply, of course, for other simple practical relations as Ic=B*Ib.) 

[Ratch]

If you want to say a material conducts current in direct proportion to the voltage across it, then

   I = (1/R) · V

is a precise mathematical statement of the same thing, where (1/R) is the constant of proportionality. The only difference is that the law of proportionality is in the first instance expressed in words and in the second in mathematical notation. It is the exact same statement either way.

I agree with the above statement, but how does that apply to the definition of Ohm's law?

If two statements are equivalent, and one statement is a statement of Ohm's law, then the other statement is also a statement of Ohm's law.

V=IR is not equivalent to Ohm's law.  The definition of resistance allows "R" in the equation to vary widely depending of the voltage and current.  Ohm's law insists that a material's voltage and current must be in direct proportion to each other.  For instance, the current vs voltage of a junction diode is a crooked curve.  It does not follow Ohm's law.  Yet it follows V=IR at all points on the curve.  Therefore, V=IR is not a definition of Ohm's law.  It is instead a definition of resistance.

In physics, pressure has dimensions of energy per unit volume, but this is not a commonly useful way to think about pressure. Hence 1 Pa is usually defined as 1 N/m² rather than 1 J/m³.

Nope, those are different units.  I challenge you to show me a link or other proof describing pressure defined that way.

Well, you can work it out: 1 J/m³ = 1 Nm/m³ = 1 N/m². The units are identical. The identity of pressure with energy per unit volume is very important in physics and engineering.

That is a perfect example of sophistry.  Just because two physical quantities have the same units does not mean they are equivalent.  For instance, torque has units of newton-meters, which is the same as units of translational energy. No one would say that torque is energy just because it has the same physical units, would they?  Identical physical quantities must have the same units, but two quantities having the same units does not necessarily mean they are equivalent.

But "electrical pressure" is nothing but voltage. You will find voltage described as electrical pressure in physics texts.

It works like this. Pressure is energy per unit volume (J/m³) and voltage is energy per unit charge (J/C). Both pressure and voltage are forms of energy density. Both pressure and voltage are also forms of motive force or potential (hence voltage differences are often referred to as EMF--electromotive force, or as PD--potential difference).

There is a lot of misinformation in textbooks and tech literature.  As I said before, just because two quantities have the same units does not mean they are the same.  Trying to equate characteristic electrical quantities to characteristic mass quantities adds another layer of confusion to the issue.

Continuing the similarity, if I wish to move a unit volume of fluid across a pressure gradient I have to do work on the fluid proportional to the difference in pressure (and in SI units the work performed is measured in joules). If I wish to move a unit of charge across a voltage gradient I have to do work on the charge proportional to the difference in voltage (and in SI units the work performed is also measured in joules).

I agree that energy is exchanged when moving a charge across different electrical energy densities.  I don't agree that moving a liquid between two different pressures causes any energy exchange.   Liquids are incompressible, so no energy is involved.  Now, if you specified a gas, then I would agree with your senario.

Such similarities between potentials and flows in different domains are very useful in physics as an aid to understanding concepts. They are something students should learn to appreciate early in their studies.

I think it is just a source of confusion.

Ratch

[helius]

Just because two physical quantities have the same units does not mean they are equivalent.  For instance, torque has units of newton-meters, which is the same as units of translational energy. No one would say that torque is energy just because it has the same physical units, would they?  Identical physical quantities must have the same units, but two quantities having the same units does not necessarily mean they are equivalent.

To be exact, torque has units of Newton × meters. It is a derived unit that is only meaningful when applied to vectors, and you cannot derive this unit from N·m because exchanging a dot for a cross product is not an allowed algebraic manipulation.
The derivation of N/m² from N·m/m³ is an allowed manipulation because a dot product is a scalar quantity.

[amyk]

Discussion about the basic principles always seem to attract a bunch of "my way is right, everyone else is wrong" arguments. I think there's a bit of bikeshedding going on. The other questions which have had similar effects here are "Which way does the current flow?" and "How does a transistor work?"