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Author Topic: Are AMPS the baddies...Not VOLTS ?  (Read 8139 times)

Offline neilep

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Are AMPS the baddies...Not VOLTS ?
« on: 23/12/2007 16:05:42 »
Hi Peeps,

What's the difference between AMPS and VOLTS ?

...and is it true that you could get a twenty thousand VOLT electric shock and if the AMPS are low enough you'll be Ok ?

Thanks

Neil
xxx


 

Offline Pumblechook

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Are AMPS the baddies...Not VOLTS ?
« Reply #1 on: 23/12/2007 17:15:07 »
May be oversimplifying but Amps are like water flow... litres per minute... and the Volts is the force pushing the water along the pipe.   

For a given bit of wire of resitance R Ohms (roughly comparable to the size of pipe and whether is smooth inside or has ridges...big smooth pipe will offer less resistance to the water flow)  a current of I amps will flow with an applied voltage of V.  A thicker wire will have a lower R. Copper will be lower R than iron.

I = V/R.   Ohms law.

Double V and I will double etc.

Halve R and I will double etc.


So a higher V means a bigger I will flow.  The path through your body makes up the R.


Some high voltage suppiles have very high 'internal' resistance and this will limit the current which will flow.   In effect the Voltage is dragged down considerably when you make a circuit through your body. 

High Voltage Overhead lines have a low internal resistance and a heafty current will flow if the touch one of them.  20,000 Volts would mean almost certain death.





 

Offline neilep

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Are AMPS the baddies...Not VOLTS ?
« Reply #2 on: 23/12/2007 17:22:06 »
FANTASTIC !!

Always humbles me to receive such awesome replies....

THANK YOU PUMBLECHOOK !!

YAYYYYYYYYYYYYYYYYYYYYYY !!
 

Offline Pumblechook

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Are AMPS the baddies...Not VOLTS ?
« Reply #3 on: 23/12/2007 17:33:39 »
Basically it is the (amps) current that kills.  But a higher voltage means a bigger current will flow.   

  For a typical female, 50 miliamps for 2/10 of a second, and for a typical male, 75 miliamps for 1/2 of a second will send the heart into ventricular fibrilation. (from a site...unconfirmed)


 
 

Offline neilep

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Are AMPS the baddies...Not VOLTS ?
« Reply #4 on: 23/12/2007 17:36:30 »
Basically it is the (amps) current that kills.  But a higher voltage means a bigger current will flow.   

  For a typical female, 50 miliamps for 2/10 of a second, and for a typical male, 75 miliamps for 1/2 of a second will send the heart into ventricular fibrilation. (from a site...unconfirmed)


 

Wow !!..that sound's so small !!

So..it's not that the body is being fried..it's just that heart is being stopped ?
 

lyner

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Are AMPS the baddies...Not VOLTS ?
« Reply #5 on: 23/12/2007 23:35:17 »
If the current flows across your chest, yes.
If you establish a good contact - (pads moistened with salt water), it doesn't require more than a few tens of volts to push 50mA through you.
If it just flows through one hand (between two high voltage terminals) you could imagine frying the hand with several amps but not stopping the heart because there were only a few milliamps flowing that way. (Poo; I smell burning)
 

Offline neilep

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Are AMPS the baddies...Not VOLTS ?
« Reply #6 on: 24/12/2007 12:34:27 »
If the current flows across your chest, yes.
If you establish a good contact - (pads moistened with salt water), it doesn't require more than a few tens of volts to push 50mA through you.
If it just flows through one hand (between two high voltage terminals) you could imagine frying the hand with several amps but not stopping the heart because there were only a few milliamps flowing that way. (Poo; I smell burning)


THANK EWE so much for this SOPHIECENTAUR.

So, what kind of amperage are they putting through your chest when they are trying to shock the heart back into pumping ?...do ewe know at all ?
 

lyner

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Are AMPS the baddies...Not VOLTS ?
« Reply #7 on: 26/12/2007 01:24:44 »
Apparently they use a 'biphase' waveform in modern defibrillators - starting with a high positive peak and then a lower negative peak. They don't seem to talk about the current but, rather, the total energy in the 'shock'.
A starting value of energy would be, apparently, 300J (joules). That would be, for example, 300W of power for 1 second, or 600W for 0.5s (power times time is energy)
For a hundred volts , you would be talking about a half second burst of 3A! That sounds an awful lot, to me. Perhaps they use a higher voltage and, thus, the current would be less  e.g. 600V 1A  or 1200V and 0.5A. Hence the "stand clear" cry when they are about to turn the thing on.
It may be that, in practice, the actual current is a lot lower - it sounds pretty savage to me; but, then, you have to give the cardiac muscles / nerves a good old belt to get them all in step again, once they have started going silly.
 

Offline Soul Surfer

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Are AMPS the baddies...Not VOLTS ?
« Reply #8 on: 30/12/2007 17:30:49 »
As an Physicist and Electrical enginer I always remember the old advice I received "Its the volts that jolts but its the mils that kills"
 

lyner

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Are AMPS the baddies...Not VOLTS ?
« Reply #9 on: 03/01/2008 23:38:15 »
I guess it's really a matter of total either charge or energy, rather than current that really counts. If the damage is due to electrolysis of cells then it would be a matter of total charge. If it is a local thermal effect then it would be a matter of energy. It's probably a combination.
According to the Green Mile film, it was a matter of frazzling the victim with loads of energy.
 

Offline Bored chemist

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Are AMPS the baddies...Not VOLTS ?
« Reply #10 on: 04/01/2008 00:47:01 »
OK, so the first reply pointed out that you can not vary the 2 parameters independently. The volts is the amps times the resistance of the body.
After that, the debate should be over. It's like saying that it's not being overweight that causes health problems; it's occupying too much volume for your height.

The true problem is complex; it's a function of disruptring nerve impulses to important things like the heart. I still have a couple of scars on my thumb where I accidentally discharged a capacitor through it. The instantaneous current was high enough to burn the tissue and the shock left me picking myself up from the far side of the room (and swearing a lot). I'm still alive (gosh!) others who had the misfortune to endure a smaller current  died because the current disrupted their heart or brain.
 

Offline that mad man

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Are AMPS the baddies...Not VOLTS ?
« Reply #11 on: 04/01/2008 20:19:20 »
The frequency of the supply is also important.

Nerve and muscle stimulation ceases at around 100khz as the frequency is too fast for the cells to pick up. Its used in Cauterisation as you don't get a "grab" effect that way.

Only found that out yesterday when I had a 50 minute colonoscopy and had 6 polyps removed using Electrocautery. Explained to the surgeon that I loved science and hoped he didn't mind me asking questions.

I even got some before and after pictures, good ones too ;D

BTW I'm a little sore today but feeling ok.  :)

Bee

 



 

Offline JimBob

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Are AMPS the baddies...Not VOLTS ?
« Reply #12 on: 04/01/2008 23:50:53 »
Gee, just playing my stereo coluld kill me is I amp up the volume. Troublesome for those like me needing mental help.

 ;)
 

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Are AMPS the baddies...Not VOLTS ?
« Reply #12 on: 04/01/2008 23:50:53 »

 

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