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FS98
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Why is the electrical potential greater before it passes through a resistor than after?
I think you are looking at things in a way that is not helpful. Electrical potential does not "pass through" a resistor, it EXISTS on one side of the resistor relative to the other and causes current to flow through the resistor. That is, electrical potential at one point is always RELATIVE to another point --- it doesn't "pass through" anything.FS98 said:Why is the electrical potential greater before it passes through a resistor than after?
My bad, that was worded poorly. I meant to ask why the electrical potential is greater at a point before the resistor than a point after the resistor.phinds said:I think you are looking at things in a way that is not helpful. Electrical potential does not "pass through" a resistor, it EXISTS on one side of the resistor relative to the other and causes current to flow through the resistor. That is, electrical potential at one point is always RELATIVE to another point --- it doesn't "pass through" anything.
If it were the other way around then the resistor would supply energy to the circuit.FS98 said:My bad, that was worded poorly. I meant to ask why the electrical potential is greater at a point before the resistor than a point after the resistor.
Do you think that's always true? I can EASILY show you a circuit where the potential "before" a resistor is 10 volts and the potential "after" the resistor is 20 volts. I think your question is more like "how can there be an electrical potential that is different at one end of a resistor than at the other end". The answer is "because some power source creates it"FS98 said:My bad, that was worded poorly. I meant to ask why the electrical potential is greater at a point before the resistor than a point after the resistor.
I could actually be less. It just depends on where your reference is. It's Potential Difference that counts.FS98 said:Why is the electrical potential greater before it passes through a resistor than after?
why does it have to do either?Dale said:If it were the other way around then the resistor would supply energy to the circuit.
That's not a suitable analogy. Potential in the moving block situation would require a sloping board (gravitational potential difference) and there is no KE involved with energy transfer by an electric current.FS98 said:why does it have to do either?
If you push a block with a constant velocity along a frictional surface, energy is being lost similarly to in the resistor. But the block doesn’t gain or lose any kinetic or potential energy as it’s pushed.
Is this situation not analogous to current through a resistor?
So is there no force on the charge carriers while going through a wire, but some force on charge carriers going through a resistor. And if so what is the cause of that force.sophiecentaur said:That's not a suitable analogy. Potential in the moving block situation would require a sloping board (gravitational potential difference) and there is no KE involved with energy transfer by an electric current.
There is a force (proportional to charge times local field) but the electrons do not speed up appreciably because they are interacting with all the positive ions. The average drift speed is around 1mm per second so not a lot of KE there for electrons with such tiny mass.FS98 said:So is there no force on the charge carriers while going through a wire, but some force on charge carriers going through a resistor. And if so what is the cause of that force.
Because if it didn’t then it wouldn’t be a resistor. It isn’t that everything has to behave that way, but things that do are called resistors and things that do not are not.FS98 said:why does it have to do either?
I dislike analogies for circuits. Circuits are so easy to understand on their own terms that there is simply no point in using analogies. The analogies are inherently flawed and almost always more complicated than circuits.FS98 said:If you push a block with a constant velocity along a frictional surface, energy is being lost similarly to in the resistor. But the block doesn’t gain or lose any kinetic or potential energy as it’s pushed.
Is this situation not analogous to current through a resistor?
phinds said:Do you think that's always true? I can EASILY show you a circuit where the potential "before" a resistor is 10 volts and the potential "after" the resistor is 20 volts. I think your question is more like "how can there be an electrical potential that is different at one end of a resistor than at the other end". The answer is "because some power source creates it"
Dale said:I dislike analogies for circuits. Circuits are so easy to understand on their own terms that there is simply no point in using analogies. The analogies are inherently flawed and almost always more complicated than circuits.
Of course you can, and what relevance does that have to this discussion?Cutter Ketch said:Uhmmm ... I suppose we can apply any definition we like to “before” and “after”, but if the potential is higher on one side of a resistor than on the other I’m pretty sure I can tell you which direction the current flows.
Because without a generous and strange definition of before and after what you implied is just wrongphinds said:Of course you can, and what relevance does that have to this discussion?
I think you're confused about who started the "before" and "after" and what was the point of my post.Cutter Ketch said:Because without a generous and strange definition of before and after what you implied is just wrong
phinds said:I think you're confused about who started the "before" and "after" and what was the point of my post.
Hydraulics are enormously more complicated than circuits.Cutter Ketch said:In particular water circuits are pretty intuitively understood by people and help them get a grasp on what is meant by current, potential, and resistance.
My experience on this forum is not so positive. We get many people who are confused in spite of or even as a result of the hydraulic analogy. Given that the thing itself is so simple, I don’t see the point of an analogy.Cutter Ketch said:I’ve always found that if they make that fundamental connection early on they never later ask about potential flowing through resistors or similar.
FS98 said:My bad, that was worded poorly. I meant to ask why the electrical potential is greater at a point before the resistor than a point after the resistor.
But you need to realize that students (especially young ones) can be very literal and will not spot a metaphor. They are often not well informed enough to spot the difference between a very limited analogy and 'the real thing'. That involves great risks of drawing false conclusions by taking an analogy too far. The water analogy is a good example which is ok for current conservation but it takes students in the direction of the erroneous "Electrical Energy is Kinetic Energy".Cutter Ketch said:I think when students are just starting out making analogies can be very helpful.
This is a great point and shows one of the problems of complicated analogies. Even in hydraulics the energy is not just kinetic energy, but people do often make exactly this mistake. They think they understand hydraulics without actually understanding it, and that flawed understanding of complicated hydraulics leads to a flawed understanding of simple circuits!sophiecentaur said:The water analogy is a good example which is ok for current conservation but it takes students in the direction of the erroneous "Electrical Energy is Kinetic Energy"
Voltage drop over a resistor is the decrease in electrical potential or voltage that occurs when current flows through a resistor. This is due to the resistance of the material in the resistor, which impedes the flow of electrons and causes a decrease in voltage.
Voltage drop over a resistor can be calculated using Ohm's Law, which states that the voltage drop (V) is equal to the current (I) multiplied by the resistance (R). This can be represented by the equation V = IR.
Voltage drop occurs over a resistor because the resistor's material has a resistance to the flow of electrons. As electrons pass through the resistor, they collide with the atoms in the material, which causes a decrease in voltage.
The resistance of the resistor directly affects the voltage drop. A higher resistance in the resistor will cause a larger decrease in voltage, while a lower resistance will result in a smaller voltage drop.
The voltage drop over a resistor can be influenced by factors such as the material and length of the resistor, the current flowing through it, and the temperature of the resistor. Additionally, the type of circuit and the presence of other resistors or components can also impact the voltage drop.