27 Replies Latest reply on Mar 3, 2018 4:06 PM by DAB

# Ohms law

To anyone who can help,

I have been recently wondering about something rather simple. Why is it in ohms law does R=V/I & I=V/R? This means that voltage is proportional to both resistance and current? I know the more voltage you have the more energy is given to each coloumb of charge but why is it that when 1 volt of energy is in 1 C of charge is there 1 ohm?

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Hi Mitchell,

Let's imagine that we have a perfect source of 10 volts with no internal resistance. What ohms law does is give us a formula for calculating the current in a circuit if we know the resistance of that circuit or the resistance of a circuit if we know the current. You can not think of Ohm's law outside the context of a circuit. If we have the 10 volt supply and we put an ammeter in the circuit and we measure 5 amps of current we can use the Ohms law to determine that the circuit has 2 Ohms of resistance. If on the other hand we put a 6 Ohm resistor across the 10 volts we will find that 1.66 Amps are flowing if we were to measure it. Let me know if I misunderstood your question.

John

10 of 10 people found this helpful
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John,

So I think you did. You reasoning was that ohms law is a group of mathematical formulas that are used to help us calculate circuit quantities as well as understand and quantify relationships between different electrical phenomenon. So your saying I have to look at Volt/current & resistance in separate ways then as a whole?

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Hi Mitchell,

In any given circuit there is a physical relationship between Voltage, Resistance, and Current. Ohm's law models this relationship mathematically. Theoretically it is possible to have a voltage without a current if there is an infinite resistance. We can not have a current without a voltage. Different materials become resistances when they become part of a circuit and convert the energy of the electron flow into heat. Since I didn't understand your last question I have tried to rephrase my previous response.

John

5 of 5 people found this helpful
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Hi Mitchell,

I think your doubts stem from the confusion between Potential Energy (measured in Joule) and difference of Potential between 2 points (measured in Volt).

When a Potential of 1 V is applied to a charge of 1 Coulomb, you have a potential energy of 1 Joule in this system. This is static energy, stored in the system (if you think of mechanics, it is like when you hold an object in your hand: the object has potential energy, due to its weight, its position and the gravity), and in this situation the charge is not moving.

Once you let the charge move, by connecting the 2 points and creating a circuit (i.e. you let the object in your hand go, and the object falls), the energy is transformed in work, which will make the charge flow into the circuit. The flow of charge in the unit of time is your current (measured in Ampere).

When you are in this situation (potential applied to a circuit, giving rise to a current flow), then you can define how "easy" or "hard" this charge can flow in the circuit (i.e. how much charge can flow, depending on physical properties of the circuit): this is what Ohm's law will tell you. Resistance measures just that.

jw0752 example explains perfectly how Ohm's law works in a circuit.

I hope this helps,

Fabio.

9 of 9 people found this helpful
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Fabio,

So in order to make electrons flow you want to make it where one point is positive and one point is negative right? So is voltage really a measurement of the positive/negative ions that are placed at opposite ends of a circuit? Because it takes energy to separate charges from neutral atoms is voltage a measurement of the amount of energy stored in the process of separating the electrons? Then when the two points are connected this makes a path for charges to equalize. How dopes ohms law take into account the physical properties of the circuit?

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Hi Mitchell,

in general, I am all for simplifying things, in order to make easier to grasp the concepts. Sometimes, though, you need to formally define entities and relationships, otherwise you end up with a lot of confusion. So, with this in mind, I will try answering your questions the best I can, while also keeping as simple as I can.

In order to have a current flowing in a conductor/circuit, it is enough that the ends of such conductor are connected to points at different potential, not necessarily to a positive and a negative. The fact that we mark the ends as + and - is a convention that has been established, just like the conventional flow for the current is established to be from positive voltage point to the negative one (while, actually, the electrons move the opposite way). Applying a voltage at the ends, let's say by connecting a battery to the conductor, you are creating a condition where there is a difference in potential.

Voltage (difference of potential between 2 points) does not represent a measurement of the quantity of positive/negative charge stored at the two ends, but rather a measurement of how much work is needed to move one unit of charge from one end to the other. In a battery, for example, the voltage of its poles does not depend on how much charge it has stored, but it is defined by the chemical elements used to build it (for the chemical reaction). It is the energy of a battery that tells you how much charge is stored in it (anyway, as you said, electrically the battery is neutral, because the amount of positive charge equals the amount of negative ones).

When you apply a voltage to the ends of a conductor, you create an electric field between the two ends. While normally, in a conductor, free electrons move randomly in all directions, with no net flow of charges (no current), when the electric field is applied, an electric force is applied to the free electrons, forcing them to ordinately move, following the direction of the field, and so generating a net flow of charge - the current.

The physical structure of the conductor determines how much current can flow:  while moving, some of the electrons collide with the conductor's ions. In the collision, the electron loses part of its kinetic energy, which is transferred to the conductor's ion. The ions of the conductor are bonded together, so this transferred energy will cause them to vibrate more (an increase in vibration means an increase in temperature for the conductor). Ultimately, the "resistivity" of an object is a measure of how much electrons are "taken out" by the collisions, and so how much the conductor "resists" to the flow of charges.

The physical properties of the conductor are taken into account with the value of the resistance R itself. In particular, for any material we can define a property called resistivity, which only depends on the physical characteristics of the material. Then, the resistance of an object R is directly proportional to the resistivity and the lenght of the object, and inversely proportional to the cross-section area of the object. In Ohm's law, R does not depend on either V or I, but it is a constant, which means that, for an obkect of know resistance R, any change in the voltage across it will result in a change is the current flowing through it.

I hope this helps,

Fabio.

7 of 7 people found this helpful
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Hi Mitchell,

You need to understand the issues involved.

Charge flow occurs when you establish a potential (EMF measured as voltage) through a conductor.

Every conductor has some level of resistance due to impurities in the material.

As the charge flows through the conductor, the mass/energy is passed from atom to atom.  The conductor atoms are arranged in a crystal structure and can easily pass each photon from atom to atom.  When the photons reach an atom of different type (impurity), that atom may emit a photon of a different type (usually IR), which reduces the amount of charge through the conductor.  That is why wires get warm when you pass a lot of current through them.  Their residual resistance caused by the impurities causes some of the current to be released as IR photons.

In a superconductor, the atoms are all at their minimum energy state, which allows them to pass the photons between atom without emitting any IR photons, but the impure atoms will release photons of higher frequencies.  So there is still some loss, but in general, even the impure atoms will mostly pass the charge with less loss.

DAB

2 of 3 people found this helpful
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Not photons, electrons. And while impurities do cause resistance I'm fairly certain that electrons bouncing off the atoms of the conductor,

and imparting energy on those atoms in the form of heat is the main source of resistance in "pure" conductors.

P.S. It was Ben Franklin that first postulated that electric current was the flow of "particles" in conductors. It was over a hundred

years later that the electron was finally discovered as that particle in experiments with early cathode ray tubes.

2 of 2 people found this helpful
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Hi Gary,

No, I really meant photons.  I have done extensive research into subatomic physics over the last nine years and I have found that there is NO experimental evidence to support the idea that electrons are either a part of atoms or flow between atoms in electronic devices.

The mathematical proofs we present in my book "Reverse Engineering The Universe" show that the atom is more likely to have a shell of captured photons instead of the accepted orbiting electrons.  The photon model shows that you get a better understanding of how mass/charge flows between atoms to support all of the macro-level attributes associated with electron flow.

My photon flow model works very well to explain how and why V = I*R works at all levels from sub-atomic to Universe level events.

I know this idea runs contrary to everything everyone has been told or taught, but so far my models do a much better job of explaining actual electronic measurements at the atom and subatomic level.

DAB

4 of 4 people found this helpful
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Based on the overall success of modern electronics from over a hundred years of research by some of the greatest minds in science

and engineering I'll stick with everybody else is right and you are wrong. Thanks anyway.

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Hi Gary,

While I tend to agree with you, if one really has a scientific thought process we have to leave open the possibilities. The scientific community went 200 years believing that they had things all figured out until Einstein showed them that at high speeds and high gravities the universe is not quite as simple as Newton portrayed it. I have looked briefly at DAB  's theories and I even bought his first book. If there is merit to his new ideas, at least, at the level that I do physics it is not worth changing from my familiar view. I believe that he might have better luck explaining things if the terminology did not overlap so much between his theory and the standard model. In the end I have chosen to stay with the standard theory of physics and not try to make the transition to something new. However, at this point, I would hesitate to tell DAB that he was wrong. We have even seen instances where two seemingly competing theories turned out to simply be the same but viewed from different mathematical perspectives. The test will be when DAB can propose an experiment whose result is correctly predicted by his approach and isn't correctly predicted by the current approach. I will keep my mind open but in the meantime, for me, electricity will remain the drifting of electrons through a conductor.

John

5 of 5 people found this helpful
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Hi John,

In my latest update, I do propose a simple experiment to demonstrate my point.

Take a glass tube with two electrodes on each end and fill the tube with only Hydrogen gas.

Then apply voltage across the tube.

What you will find is a stream of photons moving between the two electrodes. If you measure the current at each end of the tube, you will find a loss of charge running through the tube as the photons are emitted.

If you use the electron model, then you should see each Hydrogen atom dissociate as an electron is ripped from its orbit, leaving a pile of protons at the bottom of the tube and little or no Hydrogen gas remaining inside the tube after a short period of operation.

So how sure can you be that electrons are flowing instead of photons?

A spectrometer shows a very wide range of photons being released between the two electrodes and a simple pressure check will show that no Hydrogen gas was lost during operation.

Since photons are released every time you draw an electrical arc, why is photon flow such a difficult idea?

Has anyone actually seen an electron flow through a wire?

Just saying.

DAB

3 of 3 people found this helpful
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Hi DAB,

When the difference in potential is put across your tube of hydrogen,  electrons are accelerated  and their increased velocities are the means by which energy is transferred to the hydrogen atoms. When there is electron - electron interaction energy is transferred to orbital electrons. These orbital electrons then emit a photon as they jump back to a lower energy level in the atom. There are cases where an electron is removed but it is quickly replaced with another and again photons of specific energies are released as it falls back into lower energy states.

I do not understand why you say that I will find a stream of photons moving between the potential difference. Photons would be undetectable and they have no reason to move as they are not affected by an electric field. I might see a source of photons between the two potential terminals but these are successfully explained by the interaction of electrons with orbital electrons and their subsequent returning to lower energy levels.

There is no need for the atoms to disassociate. Electrons are being supplied and recovered by the potential difference and the net ionization of the hydrogen gas will likely remain fairly stable. I am not sure what the characteristics are of the protons in your physics but from the standard theory they are positively charged which would cause them to repel one another. They would not accumulate at the bottom of the tube. Gasses that have a lot of ions are called a plasma and exist at very high temperatures such as your arc, in areas where the particle density is too low for easy recombination like the upper atmosphere or in places like the Sun's atmosphere where there is heat and low density. Even in plasma there is likely a net neutrality of charge.

Using an ideal gas model you may be able to calculate the amount of hydrogen in the tube by measuring temperature and pressure. I would not expect this to change under the standard model up until the point where temperature became great enough for the gas to transition to a plasma. Frankly I do not know if the ideal gas law applies to plasma.

If photons were affected by an electric field as you seem to indicate I should be able to place an electric field between my eyes and a light source and modulate the flow of the photons. This would produce a distortion that is not observed in experiments.

Your ideas are interesting and always spark a discussion. Nothing that I do or experiment with has any need to have a precise theory at the molecular level. I like

michaelkellett 's previous post as it accurately reflects how I feel. In the mean time when I feel like trying to imagine the atomic world I am comfortable with the standard theory even though I suspect that future revelations will tweak it towards more perfection without the radical change that you propose.

John

4 of 4 people found this helpful
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That is fine.

I am challenging everything everyone thinks they know about subatomic physics.

I fully understand that nearly everyone will reject my ideas and findings.

That said, the math proofs and data analysis of my theory versus conventional thought has clearly shown that I just might be right.

My wife added a warning to the book for all students to not read the book until they are out of school and ready for independent thought.

All I ask is for everyone to have an open mind and ask themselves honestly, just how well do you really understand what goes on when charge flows.  So far, I find many people really just accept the conventions, even when they defy logical conclusions.

Case in point, Werner Heisenberg claimed that you cannot measure the positon of an electron around an atom because you cannot know its position at the time of measurement.

Yet, if you take his data, he confirms the location of small mass/charge objects at roughly 10-34 meters, which is approximately the size of captured photons in my model.

My model also validated he measurements by Niels Bohr when he found that all atoms appeared to have a diameter of about .5 * 10-10 meters, which is exactly where we found the balance point of the photon shell around the atomic nucleus for all atoms.

So my work continues, but stacked up against accepted theory, I am beating the pants off all of the basic atomic assumptions.

I use element14 as a sounding board to see if I can entice knowledgeable people to interact with.

DAB

3 of 3 people found this helpful
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There is a useful Wiki article here. It goes into more detail (and history) than you need but is interesting.

You don't need to think about photons, electrons, ions or such stuff to understand and design perfectly good electronic circuits.

I visualise circuits in terms of conventional current flow all the time - I don't give damn which way the electrons are going or how fast they actually move.

MK.

4 of 4 people found this helpful
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Sorry, I don't buy into the lack of basic knowledge of electronics is good thing meme. It leads to making simple mistakes

that leave the mistake maker with no clue as to why it doesn't work or how to fix it.

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And if you have circuit design example, of the kind that the OP is reasonably likely to encounter, where the actual speed or direction of motion of electrons (or, with due respect to DAB, if they actually move at all) in a wire matters, please cite it.

To use an analogy, I know how the engine my truck works. When I'm driving it I don't think about injectors and pistons, I think about the torque demand pedal. I could run a perfectly good delivery service without knowing anything about how engines work. In the same way I can design perfectly good active RC filters without thinking about a single electron.This doesn't imply that it is good or bad to know or not know about electrons or engines - just that it doesn't always help.

To quote Einstein: "Everything should be as simple as it can be, but not simpler", the appropriate level of simplicity obviously depends on the context and the application.

MK

2 of 2 people found this helpful
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michaelkellett I'm with you.

I've managed all these years without worrying about the unseen things causing it to happen.

Quite frankly I don't really care which way they actually move, as long as something is moving there is current flowing.

For the debaters ...

I'm sure there is room for this debate, but hijacking what I would consider a reasonable question about a formula, may not be the best place.

If you want to start another conversation, I have a really humourous story to add about the possibility of thinking alternatively.

Mark

2 of 2 people found this helpful
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Hi Mark,

I am sorry about my part in the Hijack. I forgot the simple rules of the forum which state:

Never Hijack someone else's thread nor participate in such Hijack with only these few exceptions:

1. You feel like it.

2. You forgot to say something to another poster last week.

4. You need 5 more points to break into the next level.

5. The Hijack subject is really cool.

6.

Since I am out of time and need to run I would welcome help with the rest of the list. Remember this is all for the sake of science.

John

2 of 2 people found this helpful
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Except in TM where the idea is to see if we can change the subject content to soemthign entirely different.

I just think that there is room for the debate, just not in this post.

salesm21

Hopefully you've got some things to help you rearrange how you see it.

I tend to have to match things a little and then suddenly they click into place, with the thought Duuuh, why didn't I see that before ....

Mark

2 of 2 people found this helpful
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wait, is this my cue to post cat pictures again?

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Hi Mitchell,

Keep in mind that Ohm's Law and most other equations are used for simulation only and physical things are not always that simple.

If you put 10,000 volts across a 1 ohm resistor, you won't get 10,000 amps, you'll get a melted resistor.

Resistance will change due to environmental factors also, a hot resistor or motor windings, or... will have a different value than when it's cold.

Capacitance is also a moving target.  Humidity will change a capacitor's value.  Inductance is its own beast, and will change value just by being close to another part/wire/magnet/etc.  Equations are for estimating and simulating things, and are rarely correct for all circumstances.

Clear as mud??

(If you don't believe me, try measuring the resistance of mud)

Scott

2 of 2 people found this helpful
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And contrary to other peoples opinion, that's why having at least a basic understanding of the fundamentals is important.

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This means that voltage is proportional to both resistance and current

Without sidetracking into the science (it hurts my head), the formula allows you to calculate the missing item when you know the other two.

At some point someone worked out the maths and they all aligned.

I tend to like the water theories.

If you have a river that falls a long way that is the voltage (V)

The river could flow a lot of water or there is very little to slow it down/hinder the flow (R)

The amount of water flowing depends on both the amount of fall (V) and the resistance/hinderance (R)

It not possible to have lots of flow when the resistance is high, or indeed when the fall is small

Energy is a different equation or relationship, like the equations for work, etc.

Mark

1 of 1 people found this helpful
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I appreciate all the feed back and never discourage differing ideas and actually encourage the behavior. I love having someone change the way I think or is very passionate about the way things are. The reason I asked the question is that I will be going to Florida Tech next year and intend to get my dual major in Electrical engineering/Computer science. Then I want to intern at space X or maybe JPL and work on something space related. In your opinions I want to know how in depth of an understanding you think is necessary to accomplish my goals. In regards to all post up to this point it has painted a lovely picture in my mind about voltage and current. Let me just state what I believe to be true (Based on conventional theory due to my lack of understanding of physics at this time).

In order to understand I had to think of voltage in terms of resistance. When you use a multi meter to measure resistance what are you doing? You multimeter, armed with an internal source of voltage, measures how hard it is to push current though whatever your measuring. By seeing how much current was pushed through to the other side you are able to see how much resistance there is based on OHM's law.

Again thanks for all the support and keep the comments flying( No matter how off topic us nerds get)

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Hi Mitchell,

What you explain was all proper. I think you are going to be successful in your goal. I was pleased to see from your other post that you are doing something that I feel is essential to success in any field of endeavor and that is self educate. I would also encourage you to concentrate on the foundational knowledge of your goal. You may be able to get by if you don't have it but you will never regret knowing the basics and it will give you a leg up on the other students. I would recommend that you find a good text book on Physics and Calculus and start working your way through them. Most texts have the answers in the back of the book to some of the review questions. If you concentrate on these questions you will have a way to test yourself. I feel that the basic knowledge is of particular importance if you will be coding which requires that you know the complexities of the real world so that you can create the model that you are coding. In my opinion the big difference between those who get by and those who excel is the ability to self educate. I wish you the best of luck.

John

1 of 1 people found this helpful
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Hi Mitchell,

I like your plan. As someone who hired students to work part time, you first need to see what skills each company is looking for.

I always set up entry level jobs so that students could start with just the basics. If they could write software, then there was more places to start them.

Key interview tip, be positive without overselling your capabilities. Be honest and most important, demonstrate a positive attitude and willingness to be flexible.

Most of the students I hired was based on their attitude as I always had a wide range of tasks to assign them to.

Let me know if I can help in any way.

As for your multimeter question, the meter sends a specific voltage across the probes and measures the current that flows between the probes. R = V/I.

The various ranges on the meter establish different meter sensitivities for the current so that the meters could register the appropriate range.  Digital meters change the scale factor for the A/D converter and allows the software to do the work.

Electronics is fun and reasonably easy to learn. As you progress in your studies, you will find a wealth of hidden issues that dive much deeper into the real issues.  Hence my new theories and research. There is much we know, more we think we know, and a whole lot more that everyone is guessing about. Like I said, the deeper you look, the less that you find you really know.

As the others have identified, the early basics are more than good enough for you to progress into being able to do useful things with electronics. After forty years, I have to say, I have greatly enjoyed working in the field. Now that I am no longer working, I have the time to investigate all of those little issues that did not make sense when I was in school.

Good luck,

DAB

PS, I would apologize for hijacking your thread, but I have already explained that I derive a lot of entertainment from doing so, and I hate to lie.