Do electrons actually jump across contacts?

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When we connect two conductors together in a junction, do electrons actually move from one conductor to another?

Does it also affects the masses of the two conductors?circuit-analysiscurrentShareEditFollowFlagasked 17 hours agoRodion Degtyar31766 bronze badges

• 2Are you talking about the movement of charge once the connection is formed or about the spark that might appear when you make the junction? – Sredni Vashtar 15 hours ago
• 1@SredniVashtar I guess both. – Rodion Degtyar 14 hours ago
• 1Well, when you “connect” or “join” two electrical conductors “together”, actually they are not “together” but separated by by two insulator surfaces (oxidation surface on copper/brass conductor surface), and an air layer between the two insulating oxide layer. In other words, electrons need to “jump across” three insulation layers. But actually they don’t “go through” or “jump across” the layers. The electrons, also behaving as “waves” actually cheat by “tunneling through” the layers in “no time”, / to continue, … – tlfong01 11 hours ago   
• 1/ cont, … because electrons as wave don’t care/bother insulation or no insulation, they just “walk through” like a ghost, and they don’t have any idea of time or speed, they just quantum tunnel through in no time, yes, no time! / to continue, … – tlfong01 11 hours ago   
• Some confusion clarified: (1) When you join two contacts, there is no spark (very high voltage ionized current) jumping over, it is only when you disconnect the contact, then there is back EMF causing sparking current jumping over, yes I agree, in this case, you saying they are “jumping over” from one contact to the other contact. / to continue, … – tlfong01 11 hours ago   
• 1Though electrons tunnel in no time, when you join two conductors (with oxided insulating surface), say, with their other ends connected to a battery, it does take time for the “first” electron to come out the battery’s negative terminal, and the other “first” election go into the positive terminal. But the time between the two first electrons at two terminals is very very short, of the order of 10**-14 seconds, also called relaxation time. And all electrons are moving at the same time, like those parts lying on the surface of a moving belt in a mass production manufacturing plant Cheers. – tlfong01 10 hours ago   
• physics.stackexchange.com/questions/190591/… – Ben 6 hours ago
• 2@tlfong01 I would like to downvote your answer, but … oh well. – CGCampbell 3 hours ago
• youtube.com/watch?v=PXiOQCRiSp0 – Count Iblis 31 mins ago
• 1@tlfong01 please don’t try to answer questions in the comments. I suggest you delete the comments and post as an answer. – Alexandre Aubrey 2 mins ago

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3 Answers

ActiveOldestVotes20

Yes, actual electrons do move through conductors and yes, they cross boundaries like connections between two wires.

While electrons do have mass, there is no net addition of electrons through a conductor. If N electrons are added at one end you will get N out the other end for a net mass change of 0.

Keep in mind that electrons move in a reverse direction (i.e. from – to +) which is the opposite of the conventions we normally use for current from which is from + to -. Also note that electrons move quite slowly through conductors even though the electric current moves much faster. The electrons themselves move at something like 1 mm/sec in a copper wire.ShareEditFollowFlagedited 16 hours agoanswered 16 hours agojwh2096111 silver badge66 bronze badges

• 2there is no net addition of electrons through a conductor – In the electrostatic case, there is. – Reinderien 15 hours ago
• 1Yes, that’s true but I didn’t get the impression that we were talking electrostatics here. – jwh20 15 hours ago
• Sure. I suppose that’s been left ambiguous. – Reinderien 15 hours ago
• Thanks a lot for the explanation! What if you have two charged objects and we touch them together – will it change the masses of the objects when electrons move from one of them to the other? There is no closed loop in this case. – Rodion Degtyar 15 hours ago
• 1Let’s assume you have two objects, one has an electrostatic charge. By that we mean that electrons have been “forced” onto the object by some charge generator. Perhaps a Vandegraff Generator or just some carpet. We have another object with no net charge. If you touch them together the electrostatic potential will equalize and electrons will flow from the more highly charged one to the other one. Yes, the mass of each object will change in proportion to the amount of electrons that moved. – jwh20 15 hours ago
• 3Bear in mind an electron’s mass is about 1/100000000 of, say, the copper atom that loses it so you’re really not going to notice the change. – Finbarr 14 hours ago 
• The electrons move much faster, but not in the direction of the current. Like a large number of particles moving around quickly, and with almost completely directions, except for a small bias so that the average movement is what we see as current, while no electron is so slow. I would say they drift through the conductor as a cloud. – Volker Siegel 7 hours ago
• 1@VolkerSiegel that’s why it’s called drift velocity. – Arsenal 5 hours ago

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Just a short answer to get you thinking …

When we connect two conductors together in a junction, do electrons actually move from one conductor to another?

Electrical current is the flow of charge. This is stated neatly in the equationI=dQdtI=dQdt

where I is current, Q is charge and t is time.

Now consider a DC circuit with a switch. When you close the switch the current will be the same on both sides of the switch and in the same direction. It stands to reason then that the flow of charge must cross the contacts. If the resistance of the contacts is high – as is often the case due to the small contact area – then the contacts get hot as we would predict from the power equationP=I2RP=I2Rwhere R is the contact resistance.

Does it also affects the masses of the two conductors?

No. No additional mobile charge carriers are introduced. We just push the existing charge carriers along. A (poor) analogy is a bicycle chain: it transmits power but the number of links doesn’t change and it’s weight doesn’t change. To compliment @jwh20’s point about the speed of the electric wave relative to the speed of the charges, the effect of standing on the pedals is felt immediately at the back wheel even though it takes a second or two for the links to travel from the rear sprocket to the front chain ring.ShareEditFollowFlaganswered 16 hours agoTransistor131k1010 gold badges135135 silver badges297297 bronze badges

• Thanks a lot for the explanation! What if you have two charged objects and we touch them together – will it change the masses of the objects when electrons move from one of them to the other? There is no closed loop in this case. – Rodion Degtyar 15 hours ago
• Another follow-up question about current going through I high resistance contacts of a switch. Shouldn’t current decrease in this case (since resistance is too high but voltage didn’t change?). – Rodion Degtyar 15 hours ago
• @RodionDegtyar No, it’s the current that stays the same. There is a voltage drop across the contact resistance in accordance with Ohm’s law. – Finbarr 15 hours ago
• “What if you have two charged objects and we touch them together …” That’s a different question so I won’t answer it here. Ask a new question after you’ve done your research. – Transistor 15 hours ago
• This is a short answer? How is my contact Resistance defined if not by pressure et temperature? Electrical current is the flow of charge Amerage is what hurtz not voltage or resistance – Jay 7 hours ago 
• @Transistor you know if you wire up your LEDz in reverse your have a Light detector right? – Jay 7 hours ago 
• @Jay, your comment doesn’t seem to be relevant to the OP’s question but to answer your question many factors will be relevant including contact material, surface treatment, bifurcation, contamination, contact area, … – Transistor 7 hours ago
• @Transistor I have a few editz pending in this thread care to help? – Jay 7 hours ago 
• @Jay. No. You seem to be making irrelevant comments not related to the question or answers. Don’t mess. – Transistor 7 hours ago
• Let us continue this discussion in chat. – Jay 7 hours ago
• @Jay. Sorry, no. I’m not interested. – Transistor 7 hours ago
• Thought so son. Watch your tone you know it all that in reality knows no thing – Jay 7 hours ago 

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Electrons have a mass of 10−30 kg10−30 kg.

Even so, when current flows in a loop, the electrons bump in one end and bump another out the other end of the conductor, so no change in mass occurs.

Electrons can jump across contacts when the voltage is different when contact is made.

When the current is high enough you can hear it and maybe see it. Such as plugging in a mobile charger. Since it is a current loop , the jump occurs on the last of 2 contacts made which is normally V+ by design.

This sound of the arc current is actually occurring so fast that it breaks the sound barrier and makes a tiny tick or a Big Bang such as thunder from lightning. This is simply from capacitance charge or discharge and the negative resistance from ionization of the arc between the conductors.ShareEditFollowFlagedited 13 hours agoanswered 14 hours agoTony Stewart Sunnyskyguy EE75101k22 gold badges3636 silver badges142142 bronze badges

• It will not break the sound barrier under vaccum and in a other such manifold such force would result in ultra luminescence and therefor produce light not sound or thunder – Jay 7 hours ago 
• You don’t get an arc in a vacuum as there’s nothing to ionise. – Finbarr 4 hours ago
• @Finbarr to be exact in vacuum, there will be no spark, but an arc (formed by ions emitted from the electrodes) can exist under some circumstances – dominecf 4 hours ago
• @Tony “breaking the sound barrier” is not exact as no sound source actually moves (like a Concorde); you can get a cracking sound just by a sub-sonic rapid expansion (like popping a balloon). – dominecf 4 hours ago

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