A circuit consists of a battery, an open switch, and a bulb. When the switch is closed, what first causes the electrons in the bulb to move in a particular direction?

A) Electrons from the battery eventually reach the bulb (like water in an empty pipe).

B) There is a chain reaction of electrons bumping into one another (like water in a full pipe).

C) Charge on the surface of the wire rearranges and then causes an electric field in the wire, thus inducing the electrons to move.

D) Something else

Solution: D. The immediate cause of the motion of the electrons in the bulb is an electromagnetic field that is sent through space from the switch at the speed of light. In the longer term (which is not long in a typical circuit), it is surface charge on the wire that creates an electric field in the wire and causes the electrons to move. See this video: https://www.youtube.com/watch?v=oI_X2cMHNe0