Does a resistor reduce current or drop voltage?
The answer is both.
Although dabbling in electronics for years, I repeatedly failed to fundamentally understand how voltage, current, and resistance worked together in a circuit. I understood the mathematics behind Ohms law and could readily read a schematic, but somehow I consistently failed to understand if a resistor reduced the current or if the resister dropped the voltage.
Somehow, in all my “learning the basics” of electronics, every new book or article I read failed to answer this question for me. Until I realized I fundamentally misunderstood the problem, and at the same time, had a succinct answer to my own question:
The current is determined by the resistance of the entire circuit. The voltage drop of a particular resistor can then be determined by the current.
In other words - for a simple series circuit - adding up all the resistors allows Ohms law to determine the current. This current will be the same everywhere in the circuit. Now, with a known current, we can calculate how much voltage drop will occur at each resistor based on each resistors resistance (again using Ohms law).
Magic!
P.S. Another way to calculate the voltage drop is to add up all the resistors and and then find the proportion that the single resistor represents in relation to the total resistance value:
resistorProportion = resistor / allResistorsAddedTogether
vDrop = resistorProportion * V