# Why don't you get a shock from a battery?

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#### thedoc

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##### Why don't you get a shock from a battery?
« on: 27/09/2012 22:30:01 »

Hello Chris

Love the show, listen to it every week.

I have a question for you.

Why is that when you put your fingers across the terminals of a battery you don't get shocked but if you put tin foil on the contacts and touch them you do? Hmmm

Thanks,

What do you think?
« Last Edit: 27/09/2012 22:30:01 by _system »

#### CliffordK

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##### Re: Why don't you get a shock from a battery?
« Reply #1 on: 28/09/2012 00:12:11 »
Your skin has very high electrical resistance.

V=IR

I=V/R

$$\text{Current(Amps) = \frac{Voltage(Volts)}{Resistance(Ohms)}}$$

Anyway, with 12V, and high resistance, the current across/along the skin is very small.  Even with a battery that is capable of putting out 1000 amps with low resistance, the current through the skin is only a fraction of an amp.

I have heard that one can get a much higher electrical current by pricking the skin.  However, it can be EXTREMELY DANGEROUS if there is a pathway that would cross past the heart, for example from one hand to another.

#### RD

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##### Re: Why don't you get a shock from a battery?
« Reply #2 on: 28/09/2012 00:57:51 »
... Why is that when you put your fingers across the terminals of a battery you don't get shocked but if you put tin foil on the contacts and touch them you do?

You are increasing the size of the electrode by attaching metal foil to them, the greater the surface area of your skin in contact with the electrodes the lower your electrical resistance, and consequently a higher current pass through you.

Another possibility is that the Aluminium foil in contact with the not-Alumunium metal battery electrode is creating an unintentional* second battery in series with the regular battery, which would increase the voltage experienced by the person.

[ * same as when foil touches metal tooth fillings causing an electric shock  [:0] ]

Putting metal kitchen consumables on batteries is hazardous ...
http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/burning-iron-igniting-wire-wool/
« Last Edit: 28/09/2012 01:33:17 by RD »

#### imatfaal

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##### Re: Why don't you get a shock from a battery?
« Reply #3 on: 29/09/2012 19:54:10 »
You can get a tingling shock by licking the terminals of the small (about 5cm x 2 cm x 1 cm) 9v batteries.  Not that I would recommend licking batteries - although it is a weird feeling.

I think your tongue is more sensitive and of course covered with water so aid conduction
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#### evan_au

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##### Re: Why don't you get a shock from a battery?
« Reply #4 on: 30/09/2012 11:27:09 »
Could it be partly psychological?

Intact, dry skin has a breakdown voltage well above 12V, and so does not really feel 9V (but you can really feel 48V!).
In contrast, your wet tongue can detect 1.5V, and reacts badly to 9V.

Could someone have warned you that aluminium foil would sting, causing you to sweat, and increasing the skin conductivity? (Or maybe handling the foil caused some small cuts in the skin?)

#### waytogo

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##### Re: Why don't you get a shock from a battery?
« Reply #5 on: 04/10/2012 11:44:02 »
Your skin has very high electrical resistance.

Hi there, where did you find that info?