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I understand that there are three velocities in play in a circuit (I haven't studied Physics past high school so give me some rope)

  1. v1: the velocity by which the electrical field propagates through the conductor (equal to the speed of light)

  2. v2: the velocity of the free electrons in the wire. Free electrons move around randomly in a sort of Brownian motion at speeds in the order of 1000 Km /s. When no voltage is applied on the wire this random motion results in no aggregate movement of electrons.

  3. v3: a constituent velocity vector, consistent (not random) by which the free electrons move in the direction of the current. This is very small in the order of mm or even μm / s. This vector is added on the vectors of the "Brownian" motion and results in the actual flow of electrons.

My question is: when I am electrocuted which electrons actually kill me?

  1. electrons already existing inside my body that start to move under v3. This seems unlikely as they were previously moving at v2 with no harm. Also my body is not a conductor so free electrons inside my body don't make sense.
  2. electrons from the wire that pass into my body. Given that the additional speed they acquire because of the field is very small I don't see why they couldn't previously enter my body when I touched the wire (under no voltage). Also, v3 is very small so the experience of the electrocution in that scenario would have been that my finger is shocked first, then my hand, then my arm, then my shoulders. Instead an electric shock feels instantaneous.

And I haven't even considered yet that we are mostly using alternating current so no actual, net, flow of electrons into my body occurs. Can somebody clear this confusing mental model for me?

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    $\begingroup$ If you suspect your body’s interior is not a conductor, you clearly missed the primary-school slumber party where everyone gets dared to touch both terminals of a 9V battery with their tongue. See this question and links therein for discussions about when and whether it makes sense to ask about “the electrons” carrying energy in an electrical circuit. $\endgroup$
    – rob
    Jul 7 at 9:30
  • $\begingroup$ @rob so you're saying that it is free electrons that are already inside my body that kill me. If so, why didn't they kill me before when they were moving around in their "Brownian" motion with speeds in the order of 1000 m/s but they kill me now when a tiny constituent velocity vector of mere cm/s (as a result of the electrical field) is added? $\endgroup$ Jul 7 at 10:13
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    $\begingroup$ Air molecules have a “Brownian” motion with a typical speed comparable to the speed of sound, about 760 mph. A tropical storm has winds above 60 mph. Why does a tropical storm take the roof off of your house, but the random motion doesn’t? A similar question to yours. $\endgroup$
    – rob
    Jul 7 at 10:39
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    $\begingroup$ (a) Your summary of the three velocities is, in may opinion, excellent. (b) $v_3$ is usually called the "drift velocity". (c) Unlike $v_2$, $v_3$ is relevant to electrocution because mass movement of electrons in one direction can lead to changes in charge distribution, on which the functioning of the nervous system depends. I hope that you'll get a much better answer than this rather hand-waving comment. $\endgroup$ Jul 7 at 13:41

2 Answers 2

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Which electrons kill you during electrocution ?

None of them. As you say, there are already plenty of electrons and ions moving around in your body anyway, so adding a few more makes no difference.

Death from electric shock is usually caused by the electric field, which disrupts the nerve signals which control the synchronised beating of the heart muscle. This causes ventricular fibrillation which prevents the heart from pumping blood around the body and leads to death within a few minutes if not treated.

And the usual treatment for ventricular fibrillation is to administer another carefully controlled electric shock from a defibrillator, which (bizarrely) disrupts the heart's rhythm even more severely, but then allows the body's natural pacemaker to re-establish the normal rhythm (if the patient is fortunate).

A very high voltage electric shock can have other serious effects - it can actually stop the heart completely or it can cause internal and external burns.

On the other hand, an electric shock that does not pass through the heart may have no ill effects at all. And the administration of electric shocks in a range of medical treatments called electrotherapy may even have benefits for certain health conditions.

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  • $\begingroup$ Now I'm wondering if charging a person's epidermis with a few hundred moles of "static" electrons" would cause death due to overwhelming oxidation :-) $\endgroup$ Jul 7 at 14:18
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    $\begingroup$ @CarlWitthoft Just One mole is almost one hundred thousand Coulombs, and to charge a human-sized object with even one Coulomb would require hundreds of millions of Volts. I do not think you will be able to actually perform the experiment. $\endgroup$ Jul 7 at 15:06
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    $\begingroup$ @SolomonSlow LOL "challenge accepted" $\endgroup$ Jul 8 at 12:01
  • $\begingroup$ Could the electrons going into your body simply collide with it (rather than going through it), like a sledgehammer flying towards your fingers? $\endgroup$
    – Juan Perez
    Aug 3 at 11:55
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Electricity can harm you in three ways:

  1. Electricity disrupts neurological functions in your body. This can affect the heart and cause it to fail. This effect is most dangerous when the current traverses the heart.
  2. Burns. Even if someone manages to restart your heart, if you aren't taken to the hospital quickly enough or the power applied was too great, external but especially internal burns will be very harmful.
  3. Electrolysis. Electricity applied to water causes it to split from H20 to H and O2. Now, 1 and 2 would kill us long before effect 3 but that is still harmful and can cause long term pains.
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