Potential Difference Watch

AlwaysConfused11
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Quite simply - what is potential difference?
I will give you my understanding of what it is and where my confusion lies:
Potential difference is obviously the difference in potential, where potential is the electrical potential energy per unit charge at a given point. Hence, potential difference is the difference in the electrical potential energy per unit charge at two different points and results from one side of a battery being made more negative and one side being made more positive.
However, when I try to apply this explanation to actual electrical circuits, it confuses me:
For example, if electrons only have potential energy at the start of a circuit, then how can they transfer this energy to a component directly adjacent to the battery - do they not need to effectively 'fall' through the potential difference, as an object falls through a gravitational field, to gain kinetic energy (as this isn't stored energy), which it then can transfer to a component such as a lightbulb.
Also, surely there should be a potential difference between two random points on a wire in a circuit, even if there is no component between them, as some of the electron's potential energy has been converted into kinetic energy, and so the electron's have different potential energies.
I understand that the stupidity in this post is probably painful to read for most of you, but this is genuinely something that I can't get my head around, so any and all help will be truly appreciated.
Thanks.
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cakeboi
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Potential difference is caused by a charge that has been separated. The textbook definition that we all know and love is "Potential difference is the work done per unit charge", but this is also true for voltage and emf, which makes things a bit trickier.

Electrons move due to the electric field being ≠ 0. If you connect any kind of component to a power source, there is an electric field already present between the terminals of a power source. This causes electrons to move around.
Since they are moving, they have kinetic energy.

To answer your other question (do correct me if I'm wrong here), I believe that a potential difference between two points on an isolated circuit is considered to be electromotive force.

If you want a more complete understanding, check out this page here, although it can get quite complicated quickly.
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Eimmanuel
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(Original post by AlwaysConfused11)
Quite simply - what is potential difference?
I will give you my understanding of what it is and where my confusion lies:
Potential difference is obviously the difference in potential, where potential is the electrical potential energy per unit charge at a given point. Hence, potential difference is the difference in the electrical potential energy per unit charge at two different points and results from one side of a battery being made more negative and one side being made more positive.
However, when I try to apply this explanation to actual electrical circuits, it confuses me:
For example, if electrons only have potential energy at the start of a circuit, then how can they transfer this energy to a component directly adjacent to the battery - do they not need to effectively 'fall' through the potential difference, as an object falls through a gravitational field, to gain kinetic energy (as this isn't stored energy), which it then can transfer to a component such as a lightbulb.
Also, surely there should be a potential difference between two random points on a wire in a circuit, even if there is no component between them, as some of the electron's potential energy has been converted into kinetic energy, and so the electron's have different potential energies.
I understand that the stupidity in this post is probably painful to read for most of you, but this is genuinely something that I can't get my head around, so any and all help will be truly appreciated.
Thanks.
This is NOT a stupid post. It reflects the flaw on teaching current of electricity to the students and it also reflects that the teacher(s) who teaches current of electricity do not reflect on the misconceptions that generations of students are having and avoid the pitfalls.

I can see some of the prevalent misconceptions in your writing and where it is come from.

Can I know what is your level of study of physics - O-level, A-level or University?

I would write an "appropriate" reply when you answer your level of study.
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AlwaysConfused11
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(Original post by Eimmanuel)
This is NOT a stupid post. It reflects the flaw on teaching current of electricity to the students and it also reflects that the teacher(s) who teaches current of electricity do not reflect on the misconceptions that generations of students are having and avoid the pitfalls.

I can see some of the prevalent misconceptions in your writing and where it is come from.

Can I know what is your level of study of physics - O-level, A-level or University?

I would write an "appropriate" reply when you answer your level of study.
Thank you for the support , I am currently in my first year of A-level study.
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Eimmanuel
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(Original post by AlwaysConfused11)
Quite simply - what is potential difference?
I will give you my understanding of what it is and where my confusion lies:
Potential difference is obviously the difference in potential, where potential is the electrical potential energy per unit charge at a given point. Hence, potential difference is the difference in the electrical potential energy per unit charge at two different points and results from one side of a battery being made more negative and one side being made more positive.
However, when I try to apply this explanation to actual electrical circuits, it confuses me:
For example, if electrons only have potential energy at the start of a circuit, then how can they transfer this energy to a component directly adjacent to the battery - do they not need to effectively 'fall' through the potential difference, as an object falls through a gravitational field, to gain kinetic energy (as this isn't stored energy), which it then can transfer to a component such as a lightbulb.
Also, surely there should be a potential difference between two random points on a wire in a circuit, even if there is no component between them, as some of the electron's potential energy has been converted into kinetic energy, and so the electron's have different potential energies.
I understand that the stupidity in this post is probably painful to read for most of you, but this is genuinely something that I can't get my head around, so any and all help will be truly appreciated.
Thanks.
Before I “define” what is potential difference. I would advise that you drop the following concepts or thinking.

Potential energy is always associated with a system of two or more interacting particles and not of any of the individual particles within the system. When a small ball moves near the surface of the Earth under the influence of gravity, the change in the configuration of the ball-Earth system comes about largely because of the motion of the ball, so we often associate the potential energy of this system with the ball alone. As a result, we would hear people saying like “gravitational potential energy of ball…” However, this tends to give the students the impression that the ball possesses gravitational potential energy. But this impression is NOT correct. The gravitational potential energy is actually shared between the ball and the Earth. This means that electrons do not possess electrical potential energy.

An electrical component such light bulb that is connected to a battery does not get the energy from the battery via the movement of electrons! I believe in A-level physics, you would learn about drift velocity of the electron. The magnitude of the drift velocity is so small that it should give you some hints that the electrical energy cannot be transferred by electrons.

Avoid using the analogy to “understand” the concepts in the current of electricity. Why? The analogy only helps to you remember the result or the physics found in the current of electricity. All analogies have limitations. Some analogies are good in helping the students “see” the certain results, but students tend to generalise them to see other results. As a result, the students will be confused.

When you want to think of the potential difference between two points say A and B, link it to an electric field – the two points A and B are in an electric field.

The potential difference ΔV = VBVA between two points A and B in an electric field is defined as the change in electric potential energy of the system ΔU when a charge q is moved between the points divided by the charge:

ΔV = ΔU/q

The change in electric potential energy of the system is associated with the negative work done by the electrostatic force on the charge.
ΔU = −W
I assume that you know this relationship but this is unknown to you, let me know and I would explain in another post.

So we can also define the potential difference between two points in an electric field as the negative work done by the electrostatic force to move a unit charge from one point to the other.

Apply it to the circuit, we can define the potential difference across a component in a circuit as the work done to drive a unit charge through the component.
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AlwaysConfused11
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(Original post by Eimmanuel)
Before I “define” what is potential difference. I would advise that you drop the following concepts or thinking.

Potential energy is always associated with a system of two or more interacting particles and not of any of the individual particles within the system. When a small ball moves near the surface of the Earth under the influence of gravity, the change in the configuration of the ball-Earth system comes about largely because of the motion of the ball, so we often associate the potential energy of this system with the ball alone. As a result, we would hear people saying like “gravitational potential energy of ball…” However, this tends to give the students the impression that the ball possesses gravitational potential energy. But this impression is NOT correct. The gravitational potential energy is actually shared between the ball and the Earth. This means that electrons do not possess electrical potential energy.

An electrical component such light bulb that is connected to a battery does not get the energy from the battery via the movement of electrons! I believe in A-level physics, you would learn about drift velocity of the electron. The magnitude of the drift velocity is so small that it should give you some hints that the electrical energy cannot be transferred by electrons.

Avoid using the analogy to “understand” the concepts in the current of electricity. Why? The analogy only helps to you remember the result or the physics found in the current of electricity. All analogies have limitations. Some analogies are good in helping the students “see” the certain results, but students tend to generalise them to see other results. As a result, the students will be confused.

When you want to think of the potential difference between two points say A and B, link it to an electric field – the two points A and B are in an electric field.

The potential difference ΔV = VBVA between two points A and B in an electric field is defined as the change in electric potential energy of the system ΔU when a charge q is moved between the points divided by the charge:


ΔV = ΔU/q


The change in electric potential energy of the system is associated with the negative work done by the electrostatic force on the charge.
ΔU = −W
I assume that you know this relationship but this is unknown to you, let me know and I would explain in another post.

So we can also define the potential difference between two points in an electric field as the negative work done by the electrostatic force to move a unit charge from one point to the other.

Apply it to the circuit, we can define the potential difference across a component in a circuit as the work done to drive a unit charge through the component.
Thank you very much, but would you mind explaining the electric potential energy, electrostatic force relationship please?
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Eimmanuel
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(Original post by AlwaysConfused11)
Thank you very much, but would you mind explaining the electric potential energy, electrostatic force relationship please?
When a small object moves from place to place under the gravitational force of another object (massive which we assume to remain at rest), the work done by the gravitational force on the first object (that is small) depends only on the starting and finishing points and does not depend on the path taken between the points. We can describe a force that has this special property as a conservative force. This also means that change in potential energy ΔU of the system is defined as being equal to the negative of the work done by the conservative force.

ΔU = −W

The electrostatic force is conservative, and therefore there is a potential energy associated with the configuration (the relative locations of the objects) of a system in which electrostatic forces act.

https://www.khanacademy.org/science/...rvative-forces
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Eimmanuel
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I (personally) think that your "understanding" of the movement of electrons in a closed circuit similar to this OP question in physics stackexchange.

https://physics.stackexchange.com/qu...de-and-cathode
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