Ok…my concept of “electricity” is muddled…hmm…well…here goes…
We get shocks from “static electricity” cos of the voltage difference between us and the object right?.
This difference is due to imbalance charge built up right?
Same think happens to cause lightning to strike right?
Sparks happen between my skin and the plastic wall eventhough the resistance of air is very high because the voltage difference between my skin and the wall is much higher right?..somewhere like hundreds of volts right?
The voltage required to over come the resistance of human skin is abt 40V right? so…
if i charge up one side of my hand to a very high voltagerelative to the wall…flip my hand around to face a relatively very low voltage wall…will a spark arch through my hand to the wall?:eek:
I’m not sure I understand your question. Are there two walls or one? As long as the difference in potential between your hand and the surface is greater than the resistance of the air, the electricity will jump. Your body is fairly consistant as far as resistance goes, so when you’re charging up your hand you’re really charging your entire body. Whatever body part gets close enough to a lesser charged surface first will get the ouchie.
You’ve got basically the right idea but you are off by quite a bit on your numbers. If you can actually see the spark when you touch something (like a door knob) then the voltage is more in the range of 40,000 volts, not 40 volts. Lightning is several million volts. Higher voltages will arc through higher distances of air, which is why 120 volt house wiring has thicker insulation than 12 volt car wiring for the same current capacity.
Most walls are built out of non-conductive materials, but if you touch a metal file cabinet or a door knob you can easily get a shock. We have a major problem with this at work due to the type of carpet they installed. It’s very good at building up electrical charge on your body as you move. Then you touch a file cabinet or a metal legged table and ZAP!
Nishroch Order: The numbers given by engineer_comp_geek are a little off.
If you are seeing a spark, it’s probably across a gap of about 1 mm, and the voltage is about 4000 V. If the voltage was 40,000 V, you would see an enormous spark.
The relationship between voltage and spark length is given by Pashen’s law. It says that V = 3 * d + 1.35, where d is in mm and V is in kV. For example, if d = 10 mm, V = 31.35 kV, or 31,350 V.
It doesn’t kill you because the current flow is tiny.
(I don’t want anyone jumping on me here. I’ve given a simple explanation. I know Pashen’s law includes other factors, is only an empiric linearisation, etc, etc.)
You can’t just charge one side of your hand. You can charge your entire body, but not just small bits of it. Your body is a conductor, so a charge applied to the back of your hand will distribute itself all over your body.
Secondly, you probably won’t see any discharge to a “plastic wall”. You generally get discharges to conductive objects, like another person, a doorknob, a steel bookshelf.
Simple answer: You just can’t store enough charge on your body. You can only store enough to give a tiny flash. That flash doesn’t have enough energy to do anything terribly destructive to your own or the other person’s body, nor can it sustain a current large enough and long enough to disrupt nervous or heart function.
Or another way of looking at it: while the voltage is very high, the source impedance is also very, very high. It is because the source impedance is so high that only a tiny amount of current flows.
“Dangerous” shocks, if an impulse, require around 1 joule of energy. (That’s from memory, so it could be 10j instead. Defib devices use 50joules and up, so in order to fibrillate (not defib) your heart, the energy must be LESS than 50 joules.)
And it has to be applied across your chest.
To get to the 1-joule range, your body would have to be charged to around 150,000 volts. You can’t do that by scuffing your feet on the rug. The excess charge would start leaking off faster than you could build it up.
There’s one common situation where body-voltage does get that high: in Alaska in the winter, when workers slide their butts across the long plastic seats in a truck. If you slide from the drivers seat to the passenger side and then grab the door handle, BAM!, really painful shock. But the current path isn’t across your chest, so chances are that it wouldn’t be dangerous. You’d have to hold hands with another person and THEN touch the metal door.
Also, the shock must arrive at just the right time in your heartbeat wave in order to be dangerous. This “danger window” is less than a percent of the entire wave, so in order to kill someone, you’d have to zap them hundreds of times before you got ‘lucky.’