I just wanted to learn some differences between volts, amps, ohms and so forth and came up with this question. If your skin has 100k ohms resistance and the outlet is 220v wouldn't the current flowing through your body be 0.0022 amps?
Electronic – Why can sticking fingers in an electric outlet kill you
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This was one of those crap Chinese-made Mains-to-USB chargers that can be purchased for as little as US$1.50.
I've taken them apart, and they are bad, criminally bad. The isolation from mains to output is not taken seriously- not enough creepage distance, and in one of the samples I examined, there was debris inside that could cause a direct short if you shook the charger just right.
She could have been touching the earphone plug while unplugging or plugging the earphones into the phone, and perhaps a grounded Ethernet port on an otherwise plastic computer. Once you're connected to the mains, any grounded bit of metal can be lethal. Perhaps the computer was metal and grounded.. most laptops these days have a grounded chassis so either the metal, trim, an exposed screw or anything like that would suffice. Whatever the current path, the muscle contractions probably caused her to grip the conductive bits more tightly rather than flinging them away, and sealed her fate.
A Van de Graff generator can only deliver microamperes of current continuously, so the voltage was no longer 200kV or whatever after he touched it. It was probably less than 1 volt.
If you want to look at it more technically, the generator is like a constant current source of something like 10-50uA (wild guess) feeding into a capacitor and some leakage to ground (corona discharge) that occurs at high voltage. Discharging the capacitor of (the hemisphere at the top has some capacitance) and you're left with just the microamps of current, which is not remotely enough to be dangerous.
simulate this circuit – Schematic created using CircuitLab
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In Europe the rule is generally 60V DC is safe for casual contact with live conductors. Read what the IEC says: -
Extract taken from this document.
The sort of voltage level talked about in the extract isn't generally believed to sufficiently break down the skin's "high surface resistance" BUT, mains voltages are lethal because they DO break down the surface resistance and then you just have the body's internal resistance and this is only a few hundred ohms. With (say) 220V AC applied, the current can be greater than 100mA and this is really problematic: -
NEW SECTION:
An interesting and related spin off subject is the well-known effect of a human body damaging electronic circuits by static discharge. The human body is modelled as a capacitance to earth of about 100 pF. This capacitance is charged up to several kV and the discharge path into the electronics under test is via a current limiting resistor.
An important thing to note is that unless the human body directly connects to earth (a rarer situation than normal), the current flow due to touching a live wire is somewhat limited by this capacitance.
This document entitled "Measurements upon Human Body Capacitance: Theory and Experimental Setup" concludes that about 160 pF is a the human body capacitance in the following experiment: -
So if we connect to 220V 60Hz, 160 pF has an impedance of 16.6 Mohms (reactive) and would cause a reactive current of about 13.3 uA. I don't think capacitive effects are going to be very significant.