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[SOLVED] Cathode and Anode

Dhamnekar Winod

Active member
Nov 17, 2018
115
Hello,

In cathode ray discharge tube,negative electrode is cathode and positive electrode is anode.

But in case of direct current circuit, it is the positively charged terminal of a voltaic cell or storage battery that supplies current and anode is the negatively charged terminal of a voltaic cell or storage battery that supplies current.

Why?
 

Klaas van Aarsen

MHB Seeker
Staff member
Mar 5, 2012
8,780
It can indeed be a bit confusing and it's a matter of the definition.

Current (positive charge) flows away from the cathode into the electrical circuit.
Mnemonic is CCD: Cathode Current Departs.
Of course in practice we have negative electrons that are the carriers of charge.
And while current flows away from the cathode, equivalently negative electrons flow into the cathode.

It means that for a CRT, we connect the cathode to the negative pole of our power source.
Note that the cathode itself is not the negative pole.
Consequently positive charge flows from the cathode into the power source.
Equivalently, negative electrons flow from the negative pole of the power source into the cathode where they are spit out and fly into the tube.

crt.png

In a voltaic cell, current flows again away from the cathode.
Consequently the cathode itself is the plus pole of the voltaic cell.
Equivalently, the negative electrons flow from the electrical circuit into the cathode where the electrons bind to positive metal ions in the solution.

400px-Galvanic_cell_with_no_cation_flow.png
 

HallsofIvy

Well-known member
MHB Math Helper
Jan 29, 2012
1,151
You can blame Benjamin Franklin and others of that time! When initially studying static electricity and the way it moves from one place to anther (strictly speaking they weren't working with current then) they arbitrarily assigned "positive" to one pole and "negative" to the other. They did not know that it was the negatively charged electron that carried the current and got the assignment backwards.