1. May 3, 2007

h20h

Just thinking after a lecture I went to recently about why does it take a little bit of electricity to overload your body's circuits, but if you stick a 9volt battery to your tongue (do not do it LOL) why do you get a jolt but nothing really major happens?

2. May 4, 2007

lpfr

Saliva and other body fluids are saline solutions with other substances. Saline solutions conduct well electricity. When you touch your tongue with 9 volts, enough current flows for you to feel it. When you do the same thing in your skin, you feel nothing because the upper layers of skin are dry insulating (human) leather. The current in this case is hundreds of times smaller.

3. May 4, 2007

rkkane

i think he meant why doesn't it hurt your body when electricity passes through it from a 9 volt battery.

the electricity doesn't pass through anything important in your body, it passes through one part of your tongue to another part of your tongue and back out of your body into the battery again.

4. May 4, 2007

lpfr

Yes, and, in theis case, the current is too low to be a danger.

5. May 4, 2007

Integral

Staff Emeritus
It all depends on the path the current takes. If your heart is part of the current path then as little as 50mA can cause potentially fatal disruptions of the heart rhythm.

People can, and have, survive huge currents through the extremities, ....bad burns being the usual result.

I am not certain what the resistance of the human circulation system is but if the wrist to wrist resistance is less then 180 ohms a 9V battery could induce potentially fatal currents through the heart. This would require the potential being only across the blood (an IV needle in each arm) and not the skin.

Assumptions: 9V battery, 50mA fatal current:

$$R = \frac E I = \frac {9V} {.05A} = 180 Ohms$$

Last edited: May 4, 2007
6. May 5, 2007

lpfr

When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge of it is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced it to the stage of science.

Sir William Thompson, Lord Kelvin (1824-1907)

I measured the current that circulates when you touch a 9 V battery with your tongue. It begins at about 3 mA and increases rapidly to 4.6-4.8 mA.
After a few seconds the sensation goes from displeasing to painful. I did twice the measure but, after a few seconds, I decided that the current has stabilized enough (guess why?).
The measure of the resistance is useless. Ohmmeters apply a too small voltage, well under the dissociation voltage of sodium chloride, and give resistances from 400 k ohms to 2 M ohms (always for the same tongue: mine).