Caution: Power Supplies!!

[Prof. Antonio Guerrieri]

>I = E / R.
>
>This equation describes the current in a circuit.
>
>I've won several bets with people because they didn't understand this.
>Here's the bet:
>
>"I'll bet I can place my hands, one on each of the battery terminals
>of my car, (NOT RUNNING) and suffer NO ill effects."
>
>This is a 12 volt battery capable of pushing several hundred _amperes_
>of current.   ....  Given a low enough resistance load.  !!!
>
>What the other guy doesn't understand is that my body's electrical
>resistance is too high too allow sufficient current at 12 volts.
>Current is the *real* killer, but only if it can actually flow at a
>lethal level. The actual current is defined by the above equation.
>Commercial "mains" power distribution circuits always have the
>capability of pushing enormous current and are lethal because the
>body's resistance is low enough to allow lethal levels of current to
>flow.  Conversely, a jolt from a flyback transformer might not be
>lethal because the impedance of the power circuit plus your own body's
>resistance may not allow lethal current levels.  Painful, but not
>usually lethal.
>
>So, one must consider both the voltage available AND the ability to
>supply lethal current.  If the voltage of the supply is low enough,
>the body's resistance protects against the flow of lethal current.
>
>
>-- Scott Gravenhorst

Well-written... I agree
Any case, please, consider also that the body resistance is not so high
(have you never touched both the multimeter jacks with your wet hands?)as
you can expect and that the high limit of a "safe" current value should be
in the mA range (as I remember).
Two points more ;-):

- are you sure about our body is an ohmic conductor?? i.e. can you apply
the Ohm law?? ;-)

- about your beat:

>"I'll bet I can place my hands, one on each of the battery terminals
>of my car, (NOT RUNNING) and suffer NO ill effects."
>
I will no try!!! and sorry, why not running?? It is always 12 volts with
about the same current delivering ;-)

	Best regards,

Antonio