Question

Another student, Matteo, said in a class discussion that when two identical lightbulbs are connected together in series with one another and with a battery, the bulb connected closest to the negative pole of the battery would be brighter. He explained this by claiming that the second bulb would get fewer electrons because the first bulb would use up some of the electrons. The class ended, and we were unable to build the circuit to test his reasoning at that time. Why is he correct or incorrect?

Answer 1

He is incorrect. This is because when two light bulbs are connected in series together, the current through both of them will be same. This means that number of electrons passing through both the bulbs will be same in a given time period.
Also, if the first bulb uses some of the electrons, the charge conservation principle is violated. Any number of electron entering a given cross-section of wire must leave the given cross-section in order to maintain charge conservation.