Cathode/Anode confusion

[dougkaye]

I'm pretty confused about how physics defines anodes and cathodes.

Using the convention mentioned in the other threads, one way to establish the identity of a cathode is that cations migrate toward the cathode. My question is this: If you have, say, a parallel-plate capacitor, does the electric field originate at the anode and go toward the cathode? Based on electrostatics, field lines define movement of a positive charge in an electric field. So if a positive charge moves toward the cathode, that means the cathode is negatively charged and the anode is positively charged. Is that correct?

So to accelerate a negative charge from left to right (as in, say, an electron gun), the anode would have to be on right and the cathode on left? Picture of parallel plate capacitor below with field lines as part above.

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[ModernAlchemist]

I'm pretty confused about how physics defines anodes and cathodes.

Using the convention mentioned in the other threads, one way to establish the identity of a cathode is that cations migrate toward the cathode. My question is this: If you have, say, a parallel-plate capacitor, does the electric field originate at the anode and go toward the cathode? Based on electrostatics, field lines define movement of a positive charge in an electric field. So if a positive charge moves toward the cathode, that means the cathode is negatively charged and the anode is positively charged. Is that correct?

So to accelerate a negative charge from left to right (as in, say, an electron gun), the anode would have to be on right and the cathode on left? Picture of parallel plate capacitor below with field lines as part above.

This is a common confusion. I'm surprised you didn't find other threads that explain this. The problem is that it's not so black and white. The discrepancy is found in what perspective you're looking at it from. For approaching mcat questions regarding this, just remember that electrons always flow from anode to cathode and cations always migrate toward the cathode.

In order to conceptualize what a cathode is, think of a cathode as a rod with a positive core. As current flows, electrons are being transported to that cathode and are accumulating on the surface of the "rod". So, over time, the negative charge will be attracting positive ions, not because of the core, which is positive, but because of the negative charge that is building up. Obviously, the opposite situation is occurring for the anode.

 

[SN2ed]

Thread moved. This type of topic belongs in the Study Q&A forum.