I have a bit of confusion over how a bulb lights up in a simple DC circuit. My book says it's because the electrons within the filament start moving as soon as a battery is connected. My book also says that voltage is the potential energy an electron has. It says it gains this energy as it moves through the battery (as this is the role of the battery). How can the electrons in the filament have energy and start moving as soon as you connect the circuit when they haven't been through the battery yet? Also, do the terminals of a battery refer to positive and negative charges or do they refer to differences in potential or both? Some sources I have read say that strictly speaking the terminals of a battery do not refer to net positive and negative charges but don't really explain why. I though redox reactions within the battery cause a difference in the number of electrons at the terminals and thus must refer to differences in net charge. Also, isn't a voltage directly caused by an electric field and electric field is caused by a net charge? Any help here would be greatly appreciated!