Planetarion Forums

Super · 22 Dec 2003, 04:59

My physics teacher once told me that it isn't actually voltage that kills you (when you die from an electric shock) but actually ampage. The reason everything is labelled "High Voltage" is because 10,000 Volts sounds more dangerous than 1.3 amps he went on to say.

Now he likes to say questioanable things to make sure we were paying attention, but I'm not really sure if this is true or not tbh. Anyone in the know?

queball · 22 Dec 2003, 05:02

"It's the volts that jolts, but it's the mills that kills."
It rhymes so it must be true.

But there's a good reason for labelling the voltage, too. Don't want unexpected sparking.

Super · 22 Dec 2003, 05:03

What does "mills" refer to?

Deepflow · 22 Dec 2003, 05:06

my physics teacher said that normal batteries could be recharged as rechargables and it was all a big conspiracy.

that cost me a CD player

queball · 22 Dec 2003, 05:07

Quote:

Originally Posted by Super

What does "mills" refer to?

Milliamps. Something like 100mA is lethal, I think. I don't know how you can test that though.

Oh, and obviously you need a high voltage to get any sort of current.

W · 22 Dec 2003, 05:10

Humans are quite effective resistors

Super · 22 Dec 2003, 05:13

I should probably mention that this Physics teacher firmly believes that you can produce the effects of drugs in your body if you tell your mind to do it. This may work, but it sort of misses out the step of how to "tell your mind" to do something.

Super · 22 Dec 2003, 05:15

He also drinks some grass juice stuff.

He is in his 30s I think, but is in remarkably good shape and has as much energy as the 'young adults' in the class. Makes me wonder if he's not actually crazy.

djbass · 22 Dec 2003, 10:18

Quote:

Originally Posted by Deepflow

my physics teacher said that normal batteries could be recharged as rechargables and it was all a big conspiracy.

that cost me a CD player

In some part it is true. When a battery is expending energy it is the result of an electro-chemical reaction between two substances within the battery (usually a metal + acid). Once the reaction has finished its course the battery is deemed to be dead. However by applying current to the battery it will cause the reaction to reverse itself and the two substances are reverted back into their original state. Some substances can do this better than others which is why re-chargeable batteries exist as they can better handle the constantly changing chemical states they are put through during the re-charge and discharge process.

=[DJ Bass]=

Androme · 22 Dec 2003, 10:26

posting "Sup" b4 Flavius does

Sup.

Ugly Monkey · 22 Dec 2003, 10:57

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Androme · 22 Dec 2003, 11:03

you keep telling yourself that Ugly.mp3 is a cool song for you...but you'll never be

Nodrog · 22 Dec 2003, 11:23

current kills, not voltage. Those van de graph (or whatever theyre called) generators that you put your hand on and your hair stands on have a very high voltage but you arent dead are you.

Nodrog · 22 Dec 2003, 11:24

Quote:

Originally Posted by Super

I should probably mention that this Physics teacher firmly believes that you can produce the effects of drugs in your body if you tell your mind to do it. This may work, but it sort of misses out the step of how to "tell your mind" to do something.

this is also true, you should listen to your teacher more.

MrL_JaKiri · 22 Dec 2003, 12:07

P = I^2R. Humans have high resistance. However, it doesn't mean that high voltage on its own won't do you much damage.

meglamaniac · 22 Dec 2003, 13:15

If it helps, think of the flow of electricity as a stream.
The current (amps) is how much water there is in the stream (how many electrons are passing through).
The potential difference (voltage) is how steep the slope the stream runs down is (how hard the electrons are being 'pushed').

So while power lines are extremely high voltage and have a very low current, they're dangerous because
a) as has been mentioned, it only takes a very low current to wreck thehuman nervous system
b) the high voltage is more than enough to overcome the resistance of the human body and ram that small current through it

This concludes todays physics lesson.
I expect last week's assignment by thursday lunchtime btw.

Ste · 22 Dec 2003, 13:37

Voltage does nothing on its own. However as your body is a resistance then a high voltage will induce a high current.

V=I*R

Voltage is just a measure of energy per unit charge while current is charge per second.

Ste · 22 Dec 2003, 13:42

Quote:

Originally Posted by Nodrog

current kills, not voltage. Those van de graph (or whatever theyre called) generators that you put your hand on and your hair stands on have a very high voltage but you arent dead are you.

It's actually charge not voltage.
A voltage has to be measured between two points, hence it's other name - potential difference.
A charge builds up on the metal bell-end shaped thing which makes your body positively charged (or negatively charged I cant remember which). As like charges repel they push away from each other - hence the hair standing on end.

By the way - current is just a flow of electrons (flowing from -ve to +ve) which is why your body ****s up when yopu get a large current.

meglamaniac · 22 Dec 2003, 14:57

On a slight sidetrack (for Nods benefit), isn't the reason that van de graph generators don't kill you because static electricity doesn't flow, and therefore can't screw with your nerves?

JetLinus · 22 Dec 2003, 15:18

Well, it DOES flow, doesn't it? From the ball to your fingertips, through your body, then to the ground. Sort of "transfer of charge"...

And I think voltage is, how much charge you can transport / deliver with 1 unit (electron). So moving charge is current. And current gets dangerous, when it goes through your body, which is only possible, if there is a high p.d. (coz as ppl said before, your body has a high resistance).

Just don't touch it ffs, it'll hurt anyway...

Jennifer · 22 Dec 2003, 16:09

Quote:

Originally Posted by Ste

It's actually charge not voltage.
A voltage has to be measured between two points, hence it's other name - potential difference.
A charge builds up on the metal bell-end shaped thing which makes your body positively charged (or negatively charged I cant remember which). As like charges repel they push away from each other - hence the hair standing on end.

Yes, but a build up of charge will cause a potential gradient.

Ste · 22 Dec 2003, 16:25

Quote:

Originally Posted by Jennifer

Yes, but a build up of charge will cause a potential gradient.

The charge will be even across the metal. So no potential gradient.

Jennifer · 22 Dec 2003, 22:32

Yes, but there will be a potential gradient between a point on the sphere and somewhere that isn't on the sphere (eg. ground), hence you being able to discharge yourself by touching something that is grounded. But yes, you're right that there's no charge flowing if you've just stuck a load of extra electrons on a sphere.

[pedant] Actually, the charge won't be evenly distributed in the metal, it will reside on the surface. [/pedant]

Phil^ · 23 Dec 2003, 00:26

Quote:

Originally Posted by Deepflow

my physics teacher said that normal batteries could be recharged as rechargables and it was all a big conspiracy.

that cost me a CD player

it IS possible however hydrogen bubbles form on the cathode i believe , increasing the pressure in the battery, leading to leakage or exploding

hence why its a bad idea, and why rechargables use something else ( Nickel-Cadmium based )

Denial · 24 Dec 2003, 01:10

Quote:

Originally Posted by Deepflow

my physics teacher said that normal batteries could be recharged as rechargables and it was all a big conspiracy.

that cost me a CD player

They can do, but you need a specially adapted Battery charger that can detect what state the battery is in, and whether it can be recharged (batteries with no power left seem to not recharge too well). My grandma bought one from australia, and its recharged supposedly unrechargeable batteries without causing them to leak.

Zar · 24 Dec 2003, 01:29

the only thing i can say to help is:

"Danger Danger High Voltage
When we touch When we kiss"

Hope that helps

Zar

MrL_JaKiri · 24 Dec 2003, 01:31

Your contribution Zar, as always, is unrivalled.

Deepflow · 24 Dec 2003, 02:28

Quote:

Originally Posted by Denial

They can do, but you need a specially adapted Battery charger that can detect what state the battery is in, and whether it can be recharged (batteries with no power left seem to not recharge too well). My grandma bought one from australia, and its recharged supposedly unrechargeable batteries without causing them to leak.

see, he forgot to mention that completely

so now i have a CD player that i can only play from mains cos trying to recharge bats in it broke the battery thing comperletely

the_dastardley_chihuahua · 24 Dec 2003, 03:41

i laughed when ste wrote 'bell-end'

Ste · 24 Dec 2003, 11:33

Quote:

Originally Posted by the_dastardley_chihuahua

i laughed when ste wrote 'bell-end'

I didn't know how else to describe it..

acropolis · 24 Dec 2003, 20:37

It's kind of like saying "bullets don't kill you, the holes they put in your head do", but whatever.

Current is proportional to voltage, so it doesn't really matter which you talk about.

Human skin is a good resistor, most of the human body isn't. There's about a kOhm in your skin, a few ohms through your bloodstream, through your heart, and back down the bloodstream, then about another kOhm coming out through the other skin layer.

Obvious question being 'how much do I need to kill someone', that depends on whether you are working DC or AC (if I remember right AC sends you into asystoly and DC just stops your heart outright). Generally for AC 100 mA (as queball said)of current through the heart is enough to screw things up, but of course sometimes it'll right itself on it's own.

Now, 10kV divided by ~ 3 kOhms is about 3.3 Amps, some fraction of which goes through the heart. Anyway.

Way back in the day I was at camp, and the showers had two peculiarities:
1. You had to hold the button down to keep the water flowing
2. The electrical system apparently got grounded into the plumbing

It was quite an invigorating shower, all the muscles in your arm violently contracting etc. But it wasn't really painful.

Kurashima · 24 Dec 2003, 20:47

Quote:

Originally Posted by Denial

They can do, but you need a specially adapted Battery charger that can detect what state the battery is in, and whether it can be recharged (batteries with no power left seem to not recharge too well). My grandma bought one from australia, and its recharged supposedly unrechargeable batteries without causing them to leak.

'sup Dan. Thought youd left these shores ....

Nusselt · 25 Dec 2003, 00:41

my physics teacher used to get uber pissed at newsreaders saying 'voltage went through someone'

MrL_JaKiri · 25 Dec 2003, 18:52

I was reading the Times Guide to the 02/03 series, in which there's a quote from Arsene Wenger saying that Luzny was 20% to play, and Seaman was 90% to play.

The person writing the match report then effectively said 'Lol he's dumb because Seaman didn't play and Luzny did so he doesn't understand probability'; the ironing is delicious (to quote the Simpsons)