# How is one amp under 1 volt different from 1 amp under 2 volts?

I have been reading about volts and about the water pressure analogy being inadequate to describe electricity, since pressure makes water increase speed and thus would mean electrons would also have an increase in speed under a larger potential, So if an electron doesn't increase in speed or have a greater kinetic energy under a larger volt, and it always carries the same charge, and current is the number of electrons passing through a point: How is one amp under 1 volt even different from 1 amp under 2 volts?

If 2 volts produce 1 amp of current, there must be a higher electrical resistance than in the case of 1 volt producing 1 amp of current.

Using your water analogy, you have increased the pressure but also added rocks which slow the water down.

• So voltage does increase the speed of electrons ? – soundslikefiziks Apr 30 '17 at 15:38
• Increasing voltage increases the current. In your scenario where the voltage increased but the current did not, something else (namely, resistance) must also have changed to decrease the current back to its original value. – Benitok Apr 30 '17 at 15:55
• So i know that according to ohm's law the current will increase, but the question is, why ? if the "pressure" from the voltage won't drive electrons faster why would anything be different compared to 1 volts. – soundslikefiziks Apr 30 '17 at 15:58
• It will drive the electrons faster, by which I mean they will have a higher drift velocity (you may find this interesting if you haven't heard of it: free electrons can be thought as bouncing around randomly in a wire, while a voltage causes them to drift in the direction of the wire. This drift velocity is actually very slow, on the order of micrometers per second, but this is what causes current - not the electrons' total speed. You may wonder how when you plug something in it starts charging right away if the drift velocity is so slow, well it's because there are just so many electrons). – Benitok Apr 30 '17 at 16:34
• @soundslikefiziks Yes. Again, note that it's their drift velocity (velocity component in the direction of the wire) that is increased in proportion with the voltage, while their total speed remains practically the same. To see this, imagine electrons bouncing up and down inside a wire (so they're not moving along the wire) with a speed of 200,000 m/s. Now suppose a voltage gives the electrons a horizontal velocity along the wire of 1 m/s (unrealistically large). There will be lots of current, but if you calculate their total speeds you will get 200,000.000003 m/s, not a significant change. – Benitok Apr 30 '17 at 16:54

This is the analogy I think of (No, not the water pressure one) but I only took a couple intro physics classes in college so please correct me if this analogy is completely off..

If voltage is the energy difference between two points and amperage (ampere?) is the number of electrons traveling between these two points then we could think of it as a deep well that we are dropping rocks down.

Increasing amps means we start dropping bigger rocks down this well. Increasing volts means the well gets deeper.

This analogy gives you an intuition about why static electricity (high voltage, low amps) is isn't dangerous: imagine throwing a handful of sand down a super deep well.

Also, you can apply it to situations of low voltage & super amps ie if we connected 1000 mostly dead batteries in parallel: imagine a huge boulder hovering a centimeter off the ground, it'd kill you if you got under it but that won't happen easily (but it might destroy your finger).

In your situation, it's the same size rock being dropped but there's a greater energy difference between where it is and where it will be when you release (discharge) it.

The answer from @Benitok is nicely short and good, but it seems you still have some doubts. Allow me therefore to give my take on an explanation.

How is one amp under 1 volt different from 1 amp under 2 volts?

It isn't. 1 amp of current is 1 amp of current. But it can of course be produced in different ways. Which might cause more heat waste or other energy loss. But 1 amp is 1 amp nevertheless.

Think about your shower tap. During the years it clogs with chalk. Less water comes through. The water pressure didn't change, but less water comes through now that the resistance against the water flow is higher. To still get the same water out, you will have to turn up the tap and increase the water pressure. In this way different pressures can give the same amount of flow - simply because of different resistances along the way.

What in this way happens along the way in order to create a specific flow can vary. Same for electric circuits. The big difference here is just, that even through the current is the same, more waste heat might be produced depending on how this current is made. (Higher voltage increases the power release)

• I understand the water analogy with respect to pressure increasing and thus increasing speed, but my doubts are with relation to kinetic energy in electrons, in the water analogy, the pressure from the tank gives more energy to the molecules to move through the barrier, but if electrons do not gain kinetic energy (or as minimal drift energy as @Benitok mentioned) where is that extra energy that "helps" them move through the resistor when the voltage is increased ? – soundslikefiziks Apr 30 '17 at 17:13
• @soundslikefiziks It is lost as heat. All energy not turning into kinetic, turns into heat (or is stored or alike). – Steeven Apr 30 '17 at 17:21
• So they do gain kinetic energy and dissipate it as heat because of collisions inside the resistor (and some in the wires)? – soundslikefiziks Apr 30 '17 at 17:24
• @soundslikefiziks The drift speed has to, yes. Current is charge per second. So double current means double as much charge moving past a point on the wire every second. In other words more electrons passing every second. So, faster drifting electrons. – Steeven Apr 30 '17 at 18:05
• Typo: "clocks" should be "clogs" – zwol Apr 30 '17 at 18:39

1 amp under 1 volt, that is an expression like 1 car under 1 m water, doesn't make sense.

1 amp is a flow of a particular number of electrons through an electrical leading circuit. At every location of this circuit the flow is equal to all other points. Compared with water, it is a particular amount of water circulating in e.g. a closed tube circle.

Of course, the water will not circulate in a closed tube circle at all, it will not move at all. The same is with electronic circuit from e.g. a close wire circle. The electrons will not move at all. There will be no current, no amps.

If the water should move/circle, we need a water pump, for electrons we need a electron pump. An electron pump is e.g. a battery.

Unfortunately the tube is a flow resistance for water, the leading wire has a flow resistance for electrons. When we start a flow and stop the pump, the water will not continue flowing, the electrons will not continue flowing, they will stop flowing because of the resistance, sooner or later.

We can measure the flow resistance of a tube as well as of a electric leading material. For a water tube it is measured in pressure per amount of water flow, and for electric leading material it is measures in Volts per amount of flowing electrons, that is flowing amps.

Volts is the unit for pressure. Amps is the unit for flow of electrons, that means amps.

• Reiner, I think you made your central point best in your last sentence, which would make a great intro sentence for that reason: "Volt is the unit for pressure, amp is the unit for flow of electrons." The two are indeed separate issues, though obviously they are closely connected in that higher pressure (higher voltage) will for the same circuit almost always result in more flow (more amps). – Terry Bollinger Apr 30 '17 at 19:52