Puzzled by how the Voltage is the same across different points

[Eyal Oged]

If this is better for the HW section please tell me, sorry about that.
So Voltage is the change in potential. I'm puzzled by how potential in circuits is the same along different points until we reach a resistor - at which point the potential changes. As in, if we take two points before a resistor, there is no Voltage between them. Now I'm questioning that as well, is that true? I can't grasp it. Potential energy depends on distance, no? If there is no resistor through the path but it has gotten closer to its destination, then its potential should drop, resulting in a change of Voltage, no?

 

[russ_watters]

If this is better for the HW section please tell me, sorry about that.
So Voltage is the change in potential. I'm puzzled by how potential in circuits is the same along different points until we reach a resistor - at which point the potential changes. As in, if we take two points before a resistor, there is no Voltage between them. Now I'm questioning that as well, is that true? I can't grasp it. Potential energy depends on distance, no? If there is no resistor through the path but it has gotten closer to its destination, then its potential should drop, resulting in a change of Voltage, no?

Voltage isn't potential energy. It works more like pressure or tension.

 

[Eyal Oged]

Voltage isn't potential energy. It works more like pressure or tension.

Thanks. Yeah, I know. It's the difference in potential energy between two points. But why is there no difference in potential energy between two points which are places in different distances from the destination? I thought there would be less pressure there. And why does a resistor create a change in voltage?

 

[mjc123]

This is because we usually assume that the resistance of conducting wires is virtually zero, and the only resistance in the circuit comes from resistive components. In fact of course the wire does have a very low resistance. But if you consider two points along the wire, with a wire resistance of R between them, and a potential difference of V, then V = IR. But I is the same through the wire as through the resistor, so the voltage drop is proportional to the resistance, and if the resistance of the wire is negligible compared to that of the resistor, so is the voltage drop.

 

[russ_watters]

Yeah, I know. It's the difference in potential energy between two points.

Again: No, it isn't. That sentence doesn't even make sense!

Voltage is electrical energy per unit of charge. It has nothing to do with distance nor does it have the right units to be energy.

I thought there would be less pressure there.

Pressure in a pipe and tension in a rope don't depend on position either.

And why does a resistor create a change in voltage?

Simply put, it resists the flow of electricity. It is like a partial obstruction.

 

[Eyal Oged]

Again: No, it isn't. That sentence doesn't even make sense!

Voltage is electrical energy per unit of charge. It has nothing to do with distance nor does it have the right units to be energy.

Pressure in a pipe and tension in a rope don't depend on position either.

Simply put, it resists the flow of electricity. It is like a partial obstruction.

Ah, okay, thank you, sorry! I'm trying to get this but I really don't get it :(
Then, what does the elecrtical energy depend on? What is that electrical energy? How can one coulomb have more of it than another coulomb?

 

[russ_watters]

Ah, okay, thank you, sorry! I'm trying to get this but I really don't get it :(

No prob. It's tough to let go of a preconception. And electricity is hard because it isn't like mechanical physics. My advice is to trust what the math says until you become comfortable with it.

Then, what does the elecrtical energy depend on? What is that electrical energy?

Electrical energy is voltage times charge. Charge is related to the number of electrons moved (each has a certain charge). Voltage is often referred to as "electromotive force". It's what makes the electrons move.

How can one coulomb have more of it than another coulomb?

Because a coulomb isn't energy either. It's like asking why a gallon of water can have more energy than another gallon of water. "Gallons" is not a unit of energy.

 

[anorlunda]

@Eyal Oged , you are confusing the question by adding the word energy after potential. @russ_watters is trying to explain that electric potential is not electric energy.

However, there is an analogy between height (which is associated with potential energy in a gravity field) and electric potential. Consider a ball that role across a table, then down a ramp to the destination. The flat table top is analogous to the wire in your example. The height remains constant until you come to the table edge.

But do not use the table and ball analogy for electric current or anything else electric.

 

[jim hardy]

So Voltage is the change in potential.

I sense confusion on that definition.

here's an old thread you might find helpful.

https://www.physicsforums.com/threa...s-on-an-empty-wire.903244/page-2#post-5688002

 

[Eyal Oged]

I sense confusion on that definition.

here's an old thread you might find helpful.

https://www.physicsforums.com/threa...s-on-an-empty-wire.903244/page-2#post-5688002

Thank you ;;