Why does a resistor need to be on the anode of an LED?

The resistor can be on either side of the LED, but it must be present. When two or more components are in series, the current will be the same through all of them, and so it doesn't matter which order they are in. I think the way to read "the resistor must be connected to the anode" as "the resistor cannot be omitted from the circuit."

No it would not make the resistor pointless. Imagine if the resistor were so large it completely prevented electrons from flowing. Does it matter which side of the LED it's on? Either way, it will break the circuit and prevent current from flowing.

Don't think about individual particles traveling through the circuit. The charged particles are not "used up" by the LED. They go through it, and their motion is what carries energy from one place to another.

Think about all the particles moving at all points in the circuit at once, like a belt or chain. If you slow down the chain at one point, it slows down at every other point, too, due to the links pushing and pulling against each other.

I read Getting Started in Electronics as a kid, and I think it teaches ideas like this poorly. I had to unlearn everything in college and don't recommend it. Try this instead:

• http://amasci.com/miscon/eleca.html#electron
• http://amasci.com/miscon/eleca.html#circle
• http://amasci.com/amateur/elecdir.html

Try out this circuit. When you adjust the resistance, does it only slow down the charges before the resistor, or does it change the speed of all the charges in the entire circuit?

Regardless of what side the resistor is placed on, it limits the amount of current that flows through the LED. It is usually a lot simpler to not think about what the electrons are doing and instead just think about it in sense of Resistance, Current, Voltage, and sometimes power.

In the case of an LED, if you connect a constant voltage source across the LED, the LED will act like almost 0 resistance, which will based off of V=IR (or V/R=I), will result in very large current, which causes the LED to "pop".

You have to connect a resistor in order to set the current that your LED is expecting.