Sorry for the dumb question, but I'm new to electronics and am trying to work my way through the Arduino starter kit.
If you see the attached picture you'll find a simple circuit diagram from the Arduino starter kit. The guide in the kit explains the purpose of the 10 kOhm resistor (pull-down resistor), and there are guides online which explain it further.
Overall, I think I understand the concept of a pull-down resistor, but I do not understand the purpose of the 220 Ohm resistors in this circuit diagram. There's no branching path here, the electricity is flowing through an LED and then through a 220 Ohm resistor to ground. It's not before the LEDs in the circuit, so it's not effectively limiting the current flowing through the LEDs. What is the point of the resistors here?
Graynomad:
It is limiting the LED current, no matter which side of the LED it is placed.
Rob
Ah, thanks for the explanation. All of the analogies I've seen for DC circuits show water flowing through a pipe, rocks falling down a hill, etc. They all illustrate a bottleneck only occurring at the point where you apply the resistor (and onwards), and not for the entire circuit (as seems to be the case based upon your explanation).
Every component in series applies a "bottleneck", for most purposes it doesn't matter where the devices are as the current that goes into the wire at one and must come out the other end.
One analogy I heard was to think of the circuit sort of like a bike chain. If you slow down one part of the bike chain the whole chain slows down.
As someone who is super new to electronics that seemed to help me out because I always assumed the current must flow from the positive, go in to the resistor, then through the LED. Apparently that isn't quite the case. I'm still a little unclear on it all, but I guess at this point I don't need to fully understand the why of the rules, I just need to know the rules.
Water flowing down a hill is so close to a decent analogy. But it doesn't really highlight the defining characteristic of a series circuit, that being that the current at all points of is the same.
A better analogy is water in a pipe - since pipes don't leak, it's immediately clear that the volume of water flowing through the pipe (analogous to electrical current) will be the same at any point along a pipe, regardless of where the bottleneck is.
You really need to progress to simple series/parallel circuits and Kirchoff's laws,
all will become clear, and here the required insight is that current has to be the
same all the way round a series circuit (otherwise charge would pile up)
The thing you may not realise is that charges are always balanced out to extremely
high precision, the number of electrons moving through the wire is balanced
by the positive ions stuck in the metal lattice, so the mobile electrons can only
move through, not pile up or rarify. More accurately any imbalance leads to large
electric fields so the imbalance is incredibly tiny - hence we say the current round a
series circuit is the same everywhere (an accurate approximation for most circuitry,
exceptions being things like radio antennas)
