Why Do Stun Guns Advertise Million Volt Outputs Despite 0.5 Spark Gap Limitations?

I'm not at all sure what category this fits into ...

I have been looking into stun guns for a customer (Yes I KNOW they are inhumane - it's so much better to just shoot someone like people have always done.)

The specs for stun guns are way beyond ridiculous. I've seen guns advertised that put out a million volts. Just try to buy even a 10,000 volt capacitor and fit it into a hand held unit.
I read an evaluation on police tasers and the most powerful put out 4000 volts.

The model for skin conduction has the resistance at about 500 ohms. This would be 2 kw at a million volts - a really really big battery.

Spark gaps are used to measure high voltages. A spark gap of a half inch is about what many hand held unit has. Even a gap of 1" would spark at about 30 kv with needle electrodes or about 70 kv with spherical electrodes. Once the spark is started and the gas ionized the voltage drops a lot.

I'm done with my rant - now the question. Does anyone have a simple explanation why spherical electrodes would require so much higher a voltage. Would the gap between plates be even bigger?

- Stephen

Because a pointed conductor causes a concentration of charge causing the charge density to increase considerably. This causes a rise in electromotive force and thus the breakdown point of air is reached sooner than on a sphere where the charge is evenly distributed.

Stephen,

I love a good physics problem. I'm a little rusty, but here is my understanding of it:

Charges in conductors will flow such that there is an equal potential throughout the conductor. If we were to see an unequal potential anywhere, we would see an electric field within the conductor, and the charges would 'feel' a force that would tend to move them around until the potential reaches an equilibrium state.

To say what the equilibrium state looks like based on geometry is a tricky problem. For a simple case, consider a length of wire. If we could inject, say, 100 extra electrons in to the wire, where would they go? They would repel each other, and shoot to the ends of the wire. We would expect (approximately) 50 at one end and 50 at the other, in order to maintain a constant potential throughout the wire.

More complex geometries require more complex analysis techniques, which I don't have time for here, but we see the same effect in other situations where geometry limits the positions that electrons can take to balance the potentials. Electrons, in general, tend to accumulate around sharp edges. If they did not, they would not be in equilibrium. Below is a good link showing this phenomena:

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=462.0

So: will 10KV on a shpere electrode and 10KV on a needle electrode produce the same surface potential? I should think so. However, the point of the needle electrode will have a MUCH higher charge density than the shpere, where the electrons are allowed to distribute more or less evenly over the surface. The greater point charge density on the needle electrodes would lead to a stronger electric field locally between the points, and a greater potential, making it 'easier' to ionize the air and create a spark. Think of them like lighting rods - lighting is much more likely to strike pointed metal objects for the same reason it is easier to get a spark between needle electrodes.

I don't really understand charge density. Is that the same as electron density? Electrons repel each other so itsn't the density depenent on the voltage - Isn't that the principle of a capacitor?_

In this case, the charge density on one electrode will consist of a negative charge (electrons) while the other will consist of a positive charge. All charges will behave in the same fashion in a conductor.

You make a very good point, it will indeed be dependent on voltage. And, yes, this is exactly what is happening in a capacitor, with the exception that a capacitor uses a dielectric layer to prevent arcing across the contacts.

The charge density will also be dependent on geometry of the electrodes, though. Think of it this way: equal voltages will indeed bring the same amount of charge to a needle or a sphere electrode in the same amount of time, assuming the capacitance between electrodes is the same in both cases. _However_, the charge in the needle electrode will be largely concentrated in the point. The charge _density_ (or, charge per unit volume) at that point will be much, much greater than the charge density at any point in the shpere electrode, simply because the geometry of the sphere allows the electrons to assume an equlibrium position that is more spread out. The amount of charge is about the same, but the density is very different.

Super idea when do we get to launch the next atomic missile Will it be a neutron bomb A proton bomb or should we all become komikaze pilots

Can we implant explosive devices into the human race, reprogram thier minds so they are voice activated, could we also use eye implants such that we can we can simutainuosly stream live video content at the time of inception What are the chances of changing tissue structure so that we can simply point fingers and iradiate high voltage electical impulses from thier finger tips Can we develop clones of these human models using dna copying, will they be self replicating and could we control this from the net or mobile smartphone

How soon can we deploy.

Excellent

Mark, are you sure you answered in the right thread ? I dont get the idea of your answer... How is it related to the question of Stephen ?

Quite simple encourage this You encourage civil war Give this person these answers You can bet this will wind up in the wrong hands Somwhere no matter who no matter what wether its a bonified customer or not legal or not legal

One person will move these on and they will be used to cause ultimate harm may be even kill some one

IVE SEEN THIS HAPPEN SO MANY TIMES WITH SENIOR OFFICIIALS WATCHED HOW THEY ABUSE POWER

For these reasons and these reason are good enough for me I wouldnt even think about supplying people like this that type of information simply because I know what will happen longterm I dont trust people anymore in fact very very few peopl in this country alone that I will ever trust when it comes to having that type of power

That concludes my thoughts on this already You havent seen some of this They are like bombs going off over what theyve done I definatley cant wait to see the back of some of them

Nothing but trouble

In fact should quantify this further Regretibly owing to many incidents in the uk and exposed in the press plus dealing with certain persons who are supposidly trustworthy Im afraid to say they have taught me based on experiance that are certainly not to be trusted with anything at all

bq). I wouldnt even think about supplying people like this that type of information...

How do you know what type of "people" Stephen is?

Quite simple I dont but then this isnt directed at you or about you

This is broadly based on what I know to be just shear hard and plain simple truths and lets face it When innocent people are shot by mistake in the UK by met officers and take into consideration recent riots various other, attrocities

Its common sence not to divulge that type of information on websites as its asking for trouble

Nothing personal Steve as I said before just shear hard experiance Its bad enough when officers have to arrest pshycologicaly disturbed persons who are known to have mental disorders becuase some idiot has decided to market highly dangerous weapons on the net without any control what so ever

This is complete and total disregard for public saftey

The other point im going to make is that this in the wrong hands in the uk when abused allows individuals to claim diminished responsibility and they walk out of court scot free laughing thier heads off when we know full well that they knew exactley what they were up too

We a little sick to death of that happening as well both in and out of the public sector

This is a completely irrational rant.

Stun guns aren't that dangerous, and responsible for an amazingly small number of deaths, despite urban myths to the contrary. Try reading some actual facts.

If you're really intyerested in saving lives, you could have the speed limit reduced to 10 kph, which would save countless lives, or prevent new fast food restuarants, many of which serve food that is unhealthy.

More to the point maybe people at risk, like women out alone, should stick with tried and true means of protection, such as knives. That would be much more humane.

Here recently the police shot and killed a suicidal man who was threatening to kill other people. I suppose you think it's good they didn't have access to stun gun that could have harmed him.

- Stephen

Instead of packing a stun-gun (or any gun for that matter) we should all carry a pack of gum. That way, if anyone threatens us we can whip out the pack and say, "Ya wanna stick of gum?" Then, invite them to the pub and make a friend out of them