A really (I'm guessing) simple voltage question...

[Rich Grise]

Ok, well now that we've determined that I fell victim to a bit of an
urban legend, I'm still curious why a 9 volt battery is so tiny, yet a
12 volt battery is the size of a concrete block.

The size doesn't have anything to do with the voltage. The voltage of a
given cell depends on the chemistry, and nothing else. For 9V, they
stack up little tiny 1.2V or 1.5V cells, that don't have much capacity
(as in amp-hours). Lead-acid cells are nominally 2V, so a stack of 6 of
them makes a "12V" "car" battery. The capacity is determined by the size
of the plates and amount of electrolyte that's available for the chemical
reaction, so the capacity is more-or-less proportional to the volume.

Also, something I read indicated a car battery has a sufficient CURRENT
to really hurt you, but too low a voltage. But I fail to see how that's
a true statement given Ohm's Law.

If you cut open your hands, and stuck electrodes into the open sores,
probably even a 9V battery could kill you - it only takes 15 mA through
your heart to cause fibrillation. The thing that protects you is your
skin.

Hope This Helps!
Rich

 

[Tim Williams]

wouldn't the zinc give you (hydrogen) gas?

Internally sealed. I would be more concerned about the potassium hydroxide
and (as I recall) magnanese dioxide inside alkaline batteries anyway.

Tim

 

[Eric R Snow]

The size doesn't have anything to do with the voltage. The voltage of a
given cell depends on the chemistry, and nothing else. For 9V, they
stack up little tiny 1.2V or 1.5V cells, that don't have much capacity
(as in amp-hours). Lead-acid cells are nominally 2V, so a stack of 6 of
them makes a "12V" "car" battery. The capacity is determined by the size
of the plates and amount of electrolyte that's available for the chemical
reaction, so the capacity is more-or-less proportional to the volume.


If you cut open your hands, and stuck electrodes into the open sores,
probably even a 9V battery could kill you - it only takes 15 mA through
your heart to cause fibrillation. The thing that protects you is your
skin.

Hope This Helps!
Rich

The first defibrillator was used with 110 volts AC. It was made from
two spoon shaped wands with gauze wrapped around them. These wands
were connected to a circuit in a wooden box. This circuit had rheostat
in it and I think another resistor. The circuit was connected to the
110 volt AC available in the operating room. I believe it was a 14
year old boy who benefitted from this device. The wands were placed
directly on the heart. It is now recognized that DC is much better
than AC for defibrillating the heart.
ERS