I've noticed something strange in the circuits schemes I saw in a book.
Let's say that there is an LED and it's anode is connected to a 5V power source, and it's cathode is connected to ground.
Obviously there must be a resistor between the LED's anode and the power source, but in some circuits schemes the resistor is between the LED's cathode and ground, and strangely for me, it works!
How?
I mean in the first example the resistor is before the LED so it can decrease the current so the LED doesn't burn or explode, but in the second example how can the resistor affect the delivered current to the LED and the resistor is after the LED?
The electrons will reach the LED before they reach the resistor so how can the resistor affect components behind it?
Best Answer
With components in series the same current flows through each.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Alternate series connection of resistor and LED. The result is the same.
In both circuits of Figure 1 we can see that the voltage drop across the LED is 2 V and that 7 V is dropped across the resistor. We can calculate the current from Ohm's Law, \$ I = \frac {V}{R} = \frac {7}{1k} = 7 \ \text {mA} \$. The individual components have no way of knowing their order. The current flow is determined by the total resistance of each leg of the circuit and in this example they're both the same.
Think of "current" rather than electron flow. The current flows in all parts of the circuit simultaneously in much the same way as the links of a bicycle chain all move simultaneously.