If we increase voltage, we are increasing energy per coulomb. How does it increase the number of coulombs per second (current)?
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asked Apr 5, 2020 at 17:23
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$\begingroup$ I read the question but it did not find the answers to be satisfying. The top answer says that electrons that have more energy move faster but why? Doesn’t moving faster make them lose energy? $\endgroup$– Abdulsattar MohammedCommented Apr 5, 2020 at 17:34
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$\begingroup$ Why will they loose energy when they move fast accroding to you? $\endgroup$– user316791Commented Dec 23, 2021 at 8:33
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3 Answers
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If we increase voltage, we are increasing energy per coulomb.
Consider another way of looking at voltage, as a summary of the electric field along a path between two points
$$V_{ab}=-\int_a^b {\bf E}\cdot d{\bf\ell}$$
This means if you have two fixed points, and increase the voltage between them, you must be increasing the electric field strength in the region between them.
Since the electric field is stronger, it will exert more force on charge carriers in that area, accelerating them more strongly, and thus increasing the current between the points.
answered Apr 5, 2020 at 18:03
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$\begingroup$ I like this answer, I'd only suggest that it is perhaps clearer to finish, "... thus driving an increase in current between the points." $\endgroup$ Commented Apr 5, 2020 at 18:15
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$\begingroup$ @GuyInchbald, how is what you say different from what was said in the answer? $\endgroup$ Commented Nov 12, 2021 at 13:47
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In short:
Think of voltage as an "electric pressure" on the charges. The higher the voltage, the higher the "pressure" that pushes them - so naturally, the higher is their speed, which is what we call current.
Longer version:
We all know that a ball wants to fall down from a shelf. The floor is associated with a lower (gravitational) potential energy than the shelf. Basically, any mass will always want to move towards lowest possible (gravitational) potential energy.
Same is the case for charge and (electric) potential energy. If one point in a circuit is associated with lower (electric) potential energy, then charges want to move there. A difference in (electric) potential energy thus means that there is a tendency for charges to move. This is what I mean by "electric pressure".
The difference in electric potential energy (per charge) between two points is what we have given the name voltage. Thus, the voltage directly tells us which way charges want to move - and if they can, then they will speed up in that direction, so the current will increase. This is Ohm's law.
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$\begingroup$ Got it. I was wrong in thinking the total number of charges in the wire will increase. The right way to think is that charges move faster. But why? How does increasing the potential energy make an electron move faster? Also, can you please give a more technical answer rather than using analogies? $\endgroup$ Commented Apr 5, 2020 at 17:45
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1$\begingroup$ @AbdulsattarMohammed Negative charges repel. The closer they are, the stronger they repel. Meaning, the closer they are, the more they want to move away. We have invented the concept of electric potential energy as a measure for this tendency. It that energy is very large at a point, it means that an electron is strongly repelled away from that point. If a nearby point has less potential energy then the charge is repelled less away from that point. This potential energy difference is called voltage. A voltage between two points thus means a net force from one point to the other... $\endgroup$– SteevenCommented Apr 5, 2020 at 18:12
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1$\begingroup$ @AbdulsattarMohammed ... A larger voltage means a larger net force. And naturally, a larger net force makes the charges accelerate so they reach a new and higher speed when they again are in steady-state balance. This means more electrons, more charges (so more coulomb's), moving from one point to the other per second. This is what we call current. In short: Voltage represents the electric forces on a charge, which in turn means higher current. As you say, no, we are not talking about more charges moving as before - we are talking about the same number of charges moving faster. $\endgroup$– SteevenCommented Apr 5, 2020 at 18:14
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$\begingroup$ This is wonderful, thank you so much! $\endgroup$ Commented Apr 6, 2020 at 8:58
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$\begingroup$ "A voltage between two points thus means a net force from one point to the other" that's not so correct! You can have a fixed potential difference between two point but it is not true for force. Magnitude of Electric field depends on factors like resistor's length. If you increase length you get weaker electric field amd hence weaker force on each charge particle. $\endgroup$– user316791Commented Dec 23, 2021 at 8:44
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compare the Voltage withe the pressure difference on a water pipe, if you increase the pressure, the water flows faster.
