History of electricity-


by jd12345
Tags: electricity, history
jd12345
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#1
Apr26-12, 05:36 AM
P: 260
I was studying the cathode ray experiment on how electron was discovered and the experiment uses battery for voltage.
How did the people invent battery without knowing electrons and protons ( by chance?)

And how was the name cathode and anode given without knowing which is positive and which is the negative terminal?
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DrDu
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#2
Apr26-12, 06:00 AM
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Quote Quote by jd12345 View Post
How did the people invent battery without knowing electrons and protons ( by chance?)
How did people invent drinking without knowing that water consists of molecules of H2O?
Seriously, you hardly ever need a microscopic theory to explain and exploit macroscopic phenomena.
I think you will find on the net (not to mention books) plenty of good accounts on the history of electricity. Just some key words: People were building already in the 16th century electrization machines. Benjamin Franklin coined the terms positive and negative electricity and could show their relation. Batteries were invented by Galvani and Volta.
jd12345
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Apr26-12, 06:34 AM
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Ok, stupid question ( didnt realise )
another question : Cathode is defined as the electrode where electrons enter. But the terms cathode and anode were used before discovery of electron so what did cathode and anode mean then?

DrDu
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Apr26-12, 06:56 AM
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History of electricity-


Quote Quote by jd12345 View Post
Ok, stupid question ( didnt realise )
another question : Cathode is defined as the electrode where electrons enter.
No, and even less in a chemical context. The cathode is where the reduction takes place. I.e. in a battery it is the positive pole, in an electrolytic cell it is the negative one.
So your definition only holds true for an electrolytic cell.
In electrotechnics it is (or was) defined in terms of the technical direction of the current which goes from plus to minus.
The electron is really not so important in the definition of current. E.g. in an electrolyte, current is carried by ions and, especially in case of hydronium ions, positive charge carriers may dominate. And finally in a condensator, there may be no charge carriers at all, nevertheless a displacement current can flow.
jd12345
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#5
Apr26-12, 08:00 AM
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okay - actually i'm learning(researching) about history of electricity - so just a question i mind which is troubling me:- How did they assign positive and negative terminals?

example :- In a galvanic cell zinc anode is negative and copper cathode is positive. We know this now because we know electrons flow from zinc to copper.

But how did they assign a direction to current and on what basis did they distinguish positive and negative charge?
Borek
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#6
Apr26-12, 09:00 AM
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At random. The named it this way to describe observed effects, not knowing the mechanism behind. They failed, which is a reason why electrons flow in the opposite direction to the current.

Many conventions start this way. You have to use some convention, so you select the one that suits you. Everyone else follows. Or, there are competing conventions and sooner or later one prevails, sometimes for no other reason but just because the person using one convention is more liked by people than the other.
DrDu
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Apr26-12, 09:52 AM
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Quote Quote by jd12345 View Post
example :- In a galvanic cell zinc anode is negative and copper cathode is positive. We know this now because we know electrons flow from zinc to copper.
No, we did know this long before we knew anything about electrons.
Before B. Franklin one distinguished "glassy" electricity from "resinous" electricity (I translated these terms from German, I am not sure whether it coincides with Franklins terminology) as glas rods tend to charge up positively and resins (like amber = greek "elektron") negatively. Franklin recognized that there is only one sort of electricity and created a "one fluid" theory of electricity.
He assigned "plus" to the glassy electrically charged and minus to the resinous charged bodies.
He also did chose the convention that electric current flows from plus to minus.
It is relatively easy to show that e.g. a charged glass rod will be attracted to the zinc pole of a galvanic cell, so the pole must be negatively charged. Even easier is to measure the direction of the resultant current via its magnetic effects.
jd12345
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#8
Apr26-12, 10:41 AM
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thank you guys


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