J.J. Thomson and Cathode Rays

[jadef7]

Alright, hopefully this is the correct place to post this, but the other day i was reading something about how the electron was first discovered, a man named J.J. Thomson did tests on certain gases and passed electrical current thur those gases. well, i have a few questions, and would like more clarifaction on how the procedure works.

 

So, you have a gas sealed inside of a glass tube, and they're sealed at both ends with electrodes. (what is an electrode?) and evidentally the electrodes became one anode and one cathode. when the source of electricity was turned on or whatever, the cathode(negatively charged) produced a glowing beam to the anode (positvely charged)

 

I understand this, but why does one electrode get turned into an anode, and one into a cathode? what determines it?? also, what exactly is this cathode ray? is it light? why and how is it being produced. what makes the light/beam/ray or whatever you call it. i dont really understand how light (if it is being gaven off) is produced, like what exactly is the cathode ray?

 

thanks for trying to answer this/ or read iit... and it may seem basic but I would like some clarifacation.

 

thank you!

Jade

[Mr Skeptic]

An electrode is basically just the end of an electric wire. You can just use the plain end of a wire as an electrode but usually there's a benefit to using a fancier material or special shape. The direction of current determines which is the cathode and which is the anode. People sometimes talk about the charge as determining that, but then it is opposite if it is a battery.

 

http://en.wikipedia.org/wiki/Electrode

An electrode in an electrochemical cell is referred to as either an anode or a cathode (words that were also coined by Faraday). The anode is now defined as the electrode at which electrons leave the cell and oxidation occurs, and the cathode as the electrode at which electrons enter the cell and reduction occurs. Each electrode may become either the anode or the cathode depending on the direction of current through the cell.

 

 

As for the "cathode ray", it is a beam of electrons. Also, the old televisions and computer monitors use a cathode ray to light up the screen (via energizing phosphorescent molecules), so odds are you've owned a cathode ray.

[jadef7]

but why do we see the electrons as light or whatever? what makes us see them? why cant we see electrons outside of the electrical glass tube thing?

[insane_alien]

the electrons are bouncing off the trace quantities of gas in there making it glow.

[jadef7]

what are trace quantities? ..

[Mr Skeptic]

Gas at a low pressure, and ideally one of the sort used in the neon lights. Helium is a good choice. If the gas were to dense/at too high a pressure, the electron beam would not be able to penetrate very far into it because all the beam would hit gas molecules.

[Hearts]

what are trace quantities?

...

I would suggest you try googling it first.

Edited March 7, 2011 by Hearts

[insane_alien]

what are trace quantities? ..

 

small quantities. it stems from the early days of measurement when it was used to refer to things you knew were present, but the abundance was too small to measure ie, you could only detect traces of them

Edited March 7, 2011 by insane_alien