Lots of time I’ve heard about electricity things like: the one that kills you is the current, don’t worry about large voltages (tasers for example have thousand of voltage). But using Ohm’s Law, if the voltage is big, the current is big. Then why it’s said that about current?
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Well, in most cases it’s the current simply because it’s the physical actor on your body. But as other have pointed out, the voltage is basically the force that drives the current so the voltage is definitely part of the equation and I’ll argue that the resistance of your body is too.
Ohm’s Law: V=IR
Super simple. However, take a 5V battery. 5V doesn’t sound like a lot, right? I’d agree, “relatively” it’s pretty small. However, the resistance of the human skin is somewhere in the range of 100,000 ohms give or take. So, solve for I, R = 5/100,000 = 5uA. Super small current. Now take the same human skin and make it *wet*. The resistance falls DRASTICALLY to on the order of 100 ohms. I = 5/100 = 50mA. This is 4 orders of magnitude higher and nearly in the generally considered lethal range of 100 to 200 mA!
You can achieve a higher current in this by also increasing the voltage, i.e. pushing the current faster. A 20V battery would put you in that lethal range if your skin was wet.
But, is that the whole story? Of course not. Given enough voltage, even if your skin is dry and has 100,000 ohms of resistance, what does it take to kill you? Assuming a lethal current is 100mA, V = (100mA)(100,000) = 10,000V. That’s a fairly normal high voltage you’d find in power stations and in power supplies. He’ll, you can easily find higher than that. Easily lethal. But that current *really isn’t that high* when you consider that 10A power supplies are common.
The short of it is that all 3 factors here matter, mathematically speaking. People say it’s the current that kills because it’s the actual physical flow of electrons that stops your heart, but the reality is that the resistance of your skin and the applied voltage dictate that current so all 3 things matter.
It gets even more complicated when you figure that Ohm’s law is a vast simplification of a more complex problem. The human skin is effectively a capacitor and has a breakdown voltage of ~600V. At 600V, the resistance of your skin drops *rapidly* because the voltage is capable of ripping electrons off of the atoms in your body and your body effectively begins to act like a conductor. At that point, of course, your body will start to sustain 100s of times larger currents.
TL;DR – the voltage, the current, and the resistance are all important.
Edit: and this completely disregards AC electricity. This is generally considered more dangerous simply because the alternating current usually stimulates your muscles on and off so you typically end up accidentally gripping the electronic that’s shocking you and your muscles don’t give out. DC wears out your muscles super quickly and you’ll typically go limp and break the connection.
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