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So, I know (conventional) current goes from the + pole of the battery into the anode of the LED, leaving through the cathode and into the - pole of the battery.

However, I read the cathode is the negative end. I figured it should be exiting through the positive end, and be "conventionally repelled" away.

So you end up with a circuit like this:

  • (battery) ---> + (LED) ---> - (LED) ---> - (Battery)

Is this right? How does it make sense?

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up vote 2 down vote accepted

The definition of anode and cathode is different for different devices. The anode of a device is considered to be the terminal that the conventional current flows into and a cathode is where the current flows out from. For a conducting LED the current flows into the longer leg (positive terminal), which is why it is considered the anode, and then flows out of the shorter leg (negative terminal), which is then considered the cathode. For a discharging battery however, the cathode is the positive terminal (where conventional current flows out from) and the anode is the negative terminal (where current flows in).

You could look at it a different way and say that the cathode repels cations (positive charge) which is why conventional current flows away from it, and anodes repel anions (negative charge) thus conventional current flows towards it.

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Right! So the charge of the cathode in an LED is in terms of conventional current the positive end? –  DLA Dec 15 '12 at 11:18
    
The cathode of the LED is the negative end, as it is where the current flows out of the LED. –  Luc Dec 15 '12 at 19:58
    
That's what confuses me. Batteries repel the "positive" electricity from the positive end, and those positive particles would be attracted by a negative pole, so shouldn't they be flowing into the negative end of the LED, then exiting through the positive end and being repelled by the positive to the negative side of the battery? Or am I overthinking this? –  DLA Dec 15 '12 at 20:01
    
It is a bit confusing, but it may be easier to make a distinction between "sources" and "sinks". You could think of a battery as a "source" that sources conventional current from its positive terminal and an LED as a "sink" which sinks conventional current into its positive terminal. Its basically the difference between producing power and dissipating it. Hope that clears things up a little bit. –  Luc Dec 18 '12 at 18:41
    
That makes sense! Thanks! –  DLA Dec 18 '12 at 18:43
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