Why does voltage drop in a series circuit but current stays the same?
I struggle to wrap my head around how current and resistance can remain constant throughout the [series] circuit but voltage varies? Shouldn't the current drop with the voltage?




simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. Two 2 kΩ loads on a 10 V supply.

First thing: for a resistor, \$ I_{IN} = I_{OUT} \$. Otherwise mobile charges would pile up somewhere inside the component and this doesn't happen.
As a result of 1, current in a series circuit is the same throughout. In Figure 1 \$ I_{R1} = I_{R2} \$ and \$ I_{R3} = I_{R4} = I_{R5} \$.
Voltages is measured between two points. It is common to measure with respect to an arbitrary ground (battery negative in Figure 1) but can also be measured between any two points. VM3 shows the voltage at the top of R1 with respect to ground while VM1 shows the voltage between the terminals of R1.
The circuit consisting of R3, 4 and 5 has the same overall resistance but notice the way the voltage is divided in proportion to the value of the resistors.


Figure 2. See my answer to Intuitive interpretation of negative voltage for more on voltage references. Image original by @Transistor.