Discovery of Current Electricity

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Discovery of Current Electricity
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A great debate between two Italian scientists
about the nature of current electricity
vs
Luigi Galvani 1737-1798 (Medical doctor)
Alessandro Volta 1745 - 1827 (Physicist)
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Startedwith an unexpected observation by Galvani

• Observed twitching (??)
• of frogs legs when
• dissecting them

Click to see !
What causes the legs of a dead frog to twitch?
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More observations by Galvani
They twitched when I was dissecting the frog near
a static electricity machine!
They also twitched during thunderstorms!
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Galvanis experimental setup 1 Frogs legs
stimulated by electrical storms
Galvanis experimental setup 2 Frogs legs
stimulated by an electrostatic machine
The twitching may be connected in some way to
electricity
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Further observations
Twitching still occurred in good weather
conditions away from the static electricity
generator when he hung the dead frogs from an
iron fence by brass hooks through their spinal
cord.
Galvani began a series of investigations to test
his ideas
He transferred the garden setting to his
laboratory (with no thunderstorm or electrostatic
machine). Twitching still occurred when he laid
the frog on an iron plate and pressed the brass
hook, which passed through the spinal cord,
against the plate.
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Based on his observations, what was Galvanis
conclusion?
Observed the twitching of frogs legs during
dissection.
Further observation Twitching of frogs legs
also occurred near an electrostatic machine and
during thunderstorms.
Hypothesis The twitching is connected with
electricity.
Investigation Confirmed that the twitching still
occurred without an external supply of
electricity. (electrostatic machines and
thunderstorms)
Conclusion The electricity was inside the
animal. (He called it animal electricity)
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The electricity comes from the animal itself.

• Galvanis followers travelled all over Europe
• publicly performing the demonstrations that
• made the frogs twitch.
• They did the demonstration using different
  animals.
• The number of supporters for Galvani kept
  growing.

• However, another Italian scientist named
  Alessandro Volta was skeptical (??) of Galvanis
  explanation

Alessandro Volta
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Voltas different viewpoints
The electricity comes from outside, not from
the frog itself.

• He drew attention to the different metals used in
  Galvanis experiments.
• He suggested that the twitching could only be
  produced when two different metals were used in
  dissection or in the setup.

Alessandro Volta
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Think about these questions

• What would have happened if no one had been
  skeptical of the animal electricity theory
  proposed by Galvani?
• Since Galvani was facing the challenge by Volta,
  he had to further investigate to find more solid
  evidence for his claim. Volta also had to seek
  for more evidence to challenge Galvanis view.
• Skepticism (??) is important
• for advances in scientific knowledge.
• Suggest why Volta and Galvani had different
  theories about the same observation (twitching of
  frogs legs)?
• Lets play a game

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What does this symbol represent?
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Some people may interpret the symbol as
a sign pointing to the right.
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Musicians may interpret this symbol
as decrescendo, which means get gradually
softer
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Mathematicians may interpret this symbol as
greater than
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• Observation is not always
• objective
• Observation may be affected by personal
  background or training.

vs
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Describe this picture.
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lt Mother and Son gt
Describe this picture.
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• Observation is often affected by our background
  knowledge and what we expect to see.
• This phenomenon is described as theory-laden
  observation

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Animal electricity vs Metal electricity
Science is evidence-based. It is always evidence
that matters. Evidence can help to establish or
refute (?? ) scientific knowledge.

• Q Imagine you are Galvani, what evidence would
  you give to support your animal electricity
  theory ?
• Q Now imagine you are Volta, what evidence would
  you give to support your theory, that it is the
  two different metals that cause the twitching of
  the frogs body?

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Round One

• Galvani showed the legs could twitch even when
  two similar metals were used for the dissection.

Luigi Galvani
Click to see!
Volta argued there existed a tiny difference
between the metals even though they appeared
the same.
Alessandro Volta
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Round Two

• Galvani successfully demonstrated that the
  frogs legs could twitch in the absence of any
  metals!
• (by just touching the nerves)

Luigi Galvani
It appeared to be a piece of evidence that no one
can object to!
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In fact Galvani stimulated the sciatic nerve of
the frog
Sciatic nerve ( ???? )
Stimulating the sciatic nerve can make the frogs
legs twitch.
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Location of the sciatic nerve inside the frog
The sciatic nerve is a large nerve that runs down
the lower limb. It is the longest single nerve in
the body.
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Round Two
Galvani successfully demonstrated that the frogs
legs could twitch in the absence of any
metals! Had Galvani defeated Volta? Not
yet Galvani got rid of the metal but Volta
got rid of the whole frog!
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Round Two

• Voltas Experiment Put pieces of zinc metal and
  pieces of copper metal alternately with cotton
  pads soaked in a solution of sodium chloride
  (electrolyte) between each pair. Electricity was
  generated as shown by repeated sparks. This was
  the first electric battery in history providing
  continuous current. It was later called a Voltaic
  Pile.

Pictures of Voltaic Pile
Repeated sparks
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Do you support Galvani or Volta?

• Q Now you know all the evidence provided
• by Volta and Galvani, choose whom to
• support.
• What considerations affect your
• evaluation of the two theories?

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Galvani was defeated! (for a while)

• Reason 1 Other scientists can reproduce Voltas
  experimental work easily.
• (Just putting two metals into sodium chloride
  solution)
• Galvanis experimental work is relatively more
  difficult to repeat. (Good surgical skills are
  required to dissect and stimulate the nerve ends
  of frogs legs)
• The difficulty of reproducing evidence
• affects the acceptability of the claims.
• Scientific experiments should be
  repeatable/reproducible.

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Galvani was defeated! (for a while)
Reason 2 The electric current produced by
Voltas work could be easily demonstrated by
showing repeated sparks. However,
bioelectricity (????) in living cells is too
small and Galvani did not have the technology
(e.g. CRO) to measure the current. Actually
both Galvani and Volta were right! Limitation
of technology can hinder the development of
science.
Galvanometer
CRO
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Significance of Voltas Findings

• The Voltaic Pile was the first device that could
  produce a
• steady current. (The first electric battery in
  history)

An Italian banknote showing Voltas picture and
his Voltaic Pile to celebrate his contribution to
science.
Volta demonstrating his battery to Napoleon in
1801
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Significance of Galvanis Findings

• Galvani was the first scientist to discover that
• muscles and nerve cells produce electricity.
• Though he could not prove it due to the
• limitations of technology at that time

Galvanism (???) describes the contraction of a
muscle stimulated by an electric current. (This
effect was named by Volta to honour Galvani.)
With the help of modern technology, the function
of nerve cells and their structures are studied
in great detail nowadays.
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Scientific knowledge is tentative (????)

• Through the debate between Volta and Galvani, we
  
• learn that
• Scientific knowledge changes because of
• - New evidence
• (Voltas evidence refuted Galvanis animal
  electricity theory.)
• - Advances in technology
• (Galvanis animal electricity was
  recognized only after
• the invention of instruments for
  measuring bioelectricity.)

Can you think of more examples?
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Scientists skepticism

• Through the debate between Volta and Galvani, we
  also learn that skepticism can drive the
  development of scientific research.

Q. Can you think of recent examples where
skepticism has driven the development of
scientific knowledge?
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This story also tells us
Perseverance in investigation
Observation by chance
Insight


Not enough for success