What happens in a series circuit when more bulbs are added? (Example: I start out with a complete series circuit with 2 bulbs. Then I add in several more wires and several more bulbs & bulb holders. Now I have a complete series circuit with 5 bulbs).

when we add elements in a series circuit the voltage across each element decreases

Explanation:

In a series circuit the current the whole circuit is the same, since there is only one path,

resistance is the sum of the resistance of each element

          R_{eq} = ∑ R_i

if we write ohm's law

          V = i R_{eq}

we substitute

          V = i ∑ R_i

therefore the total voltage is

         V = ∑ i R_i = ∑ V_i

With this expression we see that the voltage decreases as we place more elements in the series circuit.

Specifically when we fear two elements the voltage across each element is

           V_i = V / 2

when we have 5 elements the voltage across each element is

           V_i = V / 5

therefore when we add elements in a series circuit the voltage across each element decreases