Elementary basics...

Thread Starter

Externet

Joined Nov 29, 2005
1,412
From the Galvani page at Wikipedia :


What materials are C and Z ? (or can be)
Are they dissimilar, equal, or examples , like copper and aluminium, and are they joined/welded behind the hand ?
 

mtonge

Joined Apr 19, 2016
87
Probably copper and zinc. You can make a primitive battery by inserting copper and zinc electrodes into a potato.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,412
Thanks.
OK; so a 'normal' galvanic cell that would have dissimilar metals submerged in electrolyte would generate a current into a load placed between the electrodes.

At the picture, there is no 'load' ; The electrolyte is the animal tissues and the current equally flows. The galvanic cell is not created from the junction of different metals behind the hand, the electrolyte is the animal tissue and the 'load' is a short circuit behind the hand. Got it.

A thermocouple behavior from the junction behind the hand is not the generating scenario applying current to the animal tissue.
 
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GopherT

Joined Nov 23, 2012
8,012
Thanks.
OK; so a 'normal' galvanic cell that would have dissimilar metals submerged in electrolyte would generate a current into a load placed between the electrodes.

At the picture, there is no 'load' ; The electrolyte is the animal tissues and the current equally flows. The galvanic cell is not created from the junction of different metals behind the hand, the electrolyte is the animal tissue and the 'load' is a short circuit behind the hand. Got it.

It is kind of a frame-of-reference issue. you can look at the short-circuit as the load or the salt bridge (tissue) as the load. either way, the electronics have to flow in the circle (circuit). I am not sure a copper/zinc single cell will make a frog's leg twitch. We needed at least 3 v if I remember correctly. Neurons work much better than electricity.

EDIT: nope, I'm wrong. The Wikipedia article says a single cell can make the frog's let twitch. We were a bunch of goofy college students trying to get a lab done - not patient enough to look for fine little movements like those old scientist. I had places to go and beer to drink.
 

MrChips

Joined Oct 2, 2009
19,382
I think that what Galvani discovered is known as the Seebeck effect.
The junction of copper and zinc is held in the hand. This most likely raised the temperature at the junction thus producing an emf.
The emf causes a current to flow in the frogs legs causing muscular contraction.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,412
That was the head scratching triggering this thread...

The animal tissue as electrolyte producing the current generation; or the thermocouple generating the current into the animal tissue.

If both, are they in series with additive potential, or substractive diminishing the effect ?
 
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BR-549

Joined Sep 22, 2013
4,940
I think the metal junction is the load. Two dissimilar metals in frog juice generates a current at the junction.
The muscle jumps due to ionic flow in frog juice.
 

KL7AJ

Joined Nov 4, 2008
2,223
I think that what Galvani discovered is known as the Seebeck effect.
The junction of copper and zinc is held in the hand. This most likely raised the temperature at the junction thus producing an emf.
The emf causes a current to flow in the frogs legs causing muscular contraction.
It could be, but you don't want to jump to any conclusions.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,412
That classroom experiment/demonstration is aimed to show the muscles are activated by electrical current, but explores nothing about the current generation...
 

GopherT

Joined Nov 23, 2012
8,012
That classroom experiment/demonstration is aimed to show the muscles are activated by electrical current, but explores nothing about the current generation...
The early experiment was thought to demonstrate that the muscle had a charge that was released by the two different types of wires. Volta came along and proved the two different metals generated a current and caused the muscle to twitch.
 

MrAl

Joined Jun 17, 2014
6,610
Hi,

It is clear from the diagram that part of the experiment involves the frog legs moving as they are shown in two different positions. Thus either doing something causes the legs to move, or moving the legs causes something else to happen. It seems more plausible that something causes the legs to move.

They tried to repeat this experiment in France around that same year, but someone ate the experiment before they could perform it :)
 
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