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Recently I got into an argument with my physics teacher over a simple subject, with this question - "What kills you, the current or the voltage?". I argue that it is the voltage that kills, not the current. His reasoning was that the size of the current determines your death because the current is what actually stops your heart, not the voltage. My argument is that the voltage is like the key that unlocks that death. For example, let's say you had a power supply with a 10 amp limit. 10 amps through the body is definitely enough to kill you. Obviously just because it has a capability of 10 amps, it doesn't mean touching the leads will instantly kill you, this is because:

Current=\frac{Voltage}{Resistance}

Let's say you have these parameters:

Scenario 1

  • Voltage: 1 V
  • Resistance: 10 kΩ

Scenario 2

  • Voltage: 230 V
  • Resistance: 10 kΩ

In Scenario 1 the current would be 0.0001 Ampere (0.1 milliampere), according to the scale below, this wouldn't even be noticeable if the current was passing through a human body.

Now lets see Scenario 2. The current would be 0.023 ampere (23 milliampere), according to the scale below, this would be very noticeable. Your muscles would begin to freeze uncontrollably, and you could have respiration and muscle paralysis, this could potentially stop your heart (killing you).

The only noticeable difference is the voltage. If the resistance remains the same but the voltage changes, the obvious factor would be the voltage that affects you. I also think that a number of factors change it too: the timing of the shock, the frequency, the type of current, etc.

At the end of the day, what I'm asking is "Is it the current responsible for the death of someone, or the voltage".

Transistor
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James Barnett
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1 Answers1

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The muscles contract from the product of the current amplitude and repetition rate of pulses up to 100 Hz. Current depends on the skin conditions for resistance, but an arc will improve that conduction from ionization.

More precisely, it is energy that the heart receives that can do permanent damage.

When a heart attack occurs, a single pulse of energy is applied to large paddles to reduce the current density and current limiting effects of skin resistance. The energy stored in the capacitance is rated by Joules= Watt-seconds E= 1/2 CV^2

Thus, the closer to the heart muscle for the direct path of current vs extremities, the lower the current is to cause interference to sinus cardiac rhythm in the hundred uA range for open-heart surgery.

If only one extremity has contact to high voltage and the return path, then the return current is distributed without flowing thru the entire body and leaks to free space by the moisture and dielectric of skin interface. This is less severe than flowing from hands to feet or side to side extremity.

Tony Stewart EE75
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  • Back when I was a EE university student (late 1980s), my brother was studying bioengineering. In one of his labs, they had to experimentally determine the frequency response of nerve tissue. I don't remember all the details of the result, but do remember it looked like the 50-60Hz power line frequencies were chosen with the express goal of injury. – Theodore Oct 06 '21 at 20:50
  • that's just coincidence. Therapeutic range is from 1 to 200 Hz for both FMS and FES functional stimuli. Actual muscular synapse signals are sinc (400 Hz) with BW of 200 Hz per impulse and then increases in rates to contract more is general case. – Tony Stewart EE75 Oct 06 '21 at 21:22
  • The heart sinus rhythm is 10% of this BW and typically 10% of the rate e.g. 60 bpm. or 40 to 180 BPM – Tony Stewart EE75 Oct 06 '21 at 21:32