4
$\begingroup$

Context:

It is a near-future sci-fi and they adopted electrolasers as main weapons, because you wouldn't need to worry about propellant, ammo etc. "Just" battery and fuel.

An electrolaser is basically a laser that punches the air so hard it makes a plasma tunnel, then instantly pass a massive electric current through this tunnel.

The laser in a electrolaser lasts two-trillionths of a second, but one could make a lot of pulses to continuously guide the electricity.


The question:

Well, I couldn't find a clear answer with that on the internet, and in this setting, they would eventually use a Faraday cage to protect themselves; But first I need to worry about this specific problem:

How much electric power I would need to "instantly" (as fast as possible) make someone drop dead?

Also, don't worry about losses during travel, the question isn't about that, just imagine that someone is literally touching the electricity.

(also, I think a "direct energy weapons" tag could be interesting)

Detail: Since a lot of people are talking about the "exit point" of the electricity, then you could imagine two electrolasers hitting the target at same time making a short-circuit through the human body.

$\endgroup$
15
  • 5
    $\begingroup$ This isn't really a worldbuilding question. Material about the dangers of electricity is widely available on the Internet. $\endgroup$
    – Philipp
    Nov 8, 2022 at 10:39
  • 4
    $\begingroup$ Electric power is not measured in volts or amps. And volts over amps, if that is what <volts/amps> are supposed to be, are called ohms when they measure resistance. $\endgroup$
    – AlexP
    Nov 8, 2022 at 10:43
  • 1
    $\begingroup$ @Tortliena: That resistance is through intact skin. If sufficient voltage is applied to cause electrical breakdown of the skin, the resistance drops to 300 ohms or so. $\endgroup$
    – AlexP
    Nov 8, 2022 at 12:42
  • 1
    $\begingroup$ Milli-amps can kill a person under the right circumstances. The higher the voltage, the harder it is to push joules into the body (your body is high resistance, high voltage runs along the surface). If you could touch a person's heart with the leads of a 9V battery, it would kill them. But that doesn't simplify this question. Electrocution as a form of capital punishment had its problems because of those complications. $\endgroup$
    – JBH
    Nov 8, 2022 at 14:21
  • 2
    $\begingroup$ Two lasers crossing with the same potential does not work. One laser has to be at a higher potential, the other laser has to be at a much lower. 'return' potential. $\endgroup$ Nov 8, 2022 at 16:45

3 Answers 3

8
$\begingroup$

'Damage' by electricity is very localized. It centers on a path from where the electrical 'bolt' entered, and where it left. If the bolt does not leave, of course, there is minimal damage because there is minimal current. There has to be a complete path from huge surplus of electrons (source), entry point, exit point, then to ground (absence of electrons).

Electrical transmission, or current, is the movement of electrons from a high concentration of free electrons to a place of low concentration of electrons.

Electrical 'damage' to the human body is mostly caused by excessive heat - the electrons moving through the body produce great quantities of heat. That is, the injury is primarily burns. If the burns are very localized - that is, the entry and exit points are very close together - the burns are generally not extensive and are not immediately fatal. However, if the 'burn' damage is in a vital organ, such as the brain or heart, the injury could be instantly fatal. But that takes a LOT of electrical energy to create that much generalized burning and thus damage. If the current is high enough (there are enough electrons), water in the tissue can be converted into steam, which causes extensive tissue damage and death. But your power pack would have to have a very big battery to supply that many electrons in a short time. Think in terms of a battery in a Tesla electric car.

Most deaths by 'electrocution' are, in fact, deaths from heart attacks and suffocation. The heart and lungs stop working, not because of the high voltage or current, but because of the disruption of normal nerve activity. The heart and lungs receive the wrong signals, get confused, and stop working properly. Neither of these are instantly fatal, if immediate first aid is supplied. However, it does not take very high current to produce this effect. Milliamps (less current than it takes to light up an LED flashlight) would do it. Think in terms of a defibrillator.

Notably, the use of a 'laser' to create the ionized path is interesting. If this laser is sufficiently powerful enough to penetrate the skin, then it is like putting a notch in the electrical insulation around a wire. There would be a minimal barrier to the electrical current INSIDE the body. However, you still need a second exit point, or ground contact, of minimal resistance to complete the circuit. The laser would not only have to go through the body, but it would have to go through the body where the body was making contact with ground, or the laser beam 'path' would have to connect to ground at its end point.

Edit addendum:

If you send two parallel beams, one at a high potential, the other at a low potential, and a needle down each beam to penetrate the skin and any clothing, one has the possibility of a neural disruptor like a stun gun without the wires.

$\endgroup$
9
  • $\begingroup$ "However, you still need a second exit point". Then I could just make two electrolasers hit the target, like putting two high voltage points of a welding machine. No? $\endgroup$
    – Fulano
    Nov 8, 2022 at 14:28
  • 1
    $\begingroup$ @Fulano You invented the stun guns, I think x)? $\endgroup$ Nov 8, 2022 at 14:39
  • 1
    $\begingroup$ @Fulano At the point of impact yes, but a metallic cable is surely more conductive than pure air, even when superheated, consider this for the power/intensity/tension at the start of your gun! $\endgroup$ Nov 8, 2022 at 14:46
  • 1
    $\begingroup$ Two lasers crossing with the same potential does not work. One laser has to be at a higher potential, the other laser has to be at a much lower. 'return' potential. $\endgroup$ Nov 8, 2022 at 16:46
  • 1
    $\begingroup$ @Fulano You would need to have those two plasma tunnels isolated from each other, otherwise the electricity won't reach the target. $\endgroup$
    – gre_gor
    Nov 9, 2022 at 7:57
6
$\begingroup$

Depends on your definition of "instant".

As little as 30 milliamps of 60 Hz ac across the chest (or less directly applied to the heart) will induce fibrillation, which will be fatal without immediate first aid (CPR and/or application of a defibrillator). This takes minutes to actually kill, but immediate loss of blood pressure will result in loss of consciousness approximately fifteen seconds.

To induce instant brain death is another matter entirely -- it would require significant amperage applied directly to the brain, sufficient to heat a significant fraction (and critical parts!) of the brain to a lethal temperature -- say, 44 C or so. This is far below lightning bolt power, but also much harder to apply than what's needed to induce fibrillation. It's actually much easier to physically disrupt the brain with a conventional projectile, and a century of "modern" military experience suggests that situations where combatants run short on ammunition are uncommon (especially so with newer, lighter cartridges and rifles).

$\endgroup$
1
$\begingroup$

A lightning strike can kill a person pretty much instantly.

So I would say that ten megavolts delivering ten kiloamperes for a very few milliseconds will be absolutely enough.

But ten megavolts is very obviously overkill. Half a megavolt would be plenty...

$\endgroup$
1
  • 2
    $\begingroup$ Or not. people have survived a direct lightning strike. It depends on where the bolt enters the body, and where it leaves. $\endgroup$ Nov 8, 2022 at 13:25

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .