How does a voltage increase/decrease affect the electric potential energy of a charge? Consider a simple series circuit with 2 light bulbs. We know that there will be a voltage drop after the current passes through the first light bulb, but the current remains the same. If we were to observe the electrons traveling the circuit before and after they reach the first light bulb, how would they differ if not by the rate they are traveling? It is obvious they have more energy before reaching the first light bulb than they do after, but what does this energy difference look like on a subatomic scale?
 A: There is absolutely no difference between the electrons.  Every electron is identical.  The difference is in the entire system of charges.
Imagine a clock that you can run by allowing a weight to fall.  What is the difference between the weight when it is raised to the top and when it has fallen to the bottom?  The weight itself is identical.  The difference is that at the top, the weight is higher in a gravitational field.  This position requires energy to reach compared to the floor.
Similarly, the circuit has an electric field and charges have different amounts of energy due to their position in the field.  
A: This is a good question. 
You see, the atoms in the wire are electrically neutral. 
Every atom in the wire has the proper number of electrons to balance the protons in 
the nucleus. 
What the current is or what happens in the wire is still a belief for most of us. 
An electron gets traded from atom to atom is one belief. 
An electron floats through the atom in a potential difference field is another belief. 
The current is decided in the circuit before the electron starts. (visibility in the 
cct happens at the speed of light / 2) 
The voltage travels through the wire normally with an electron almost at rest moving
with it. 
The voltage reduces as work is done at stages in the circuit. The electron stays in the 
field. 
Until at zero potential (actually a positive or opposite potential) it is returned to the 
source. 
Maybe this will help? 
