I know how they move in vacuum when some positive/negative charge is near them. But I have found it really difficult to visualize their movement in a wire. First I used to think that due to the presence of electric field, they move from the negative terminal to the positive. But as the wire can bend, and so it doesn't make sense since electric field are straight lines. So, I tried this model: Near the positive terminal, valence electrons are being attracted, and thus the atoms that are near the positive terminal become positive, and they attract electrons from the remaining part of the wire. This sounds more correct, but according to this, all part of the wire from the switch to the positive terminal should be charged positive when the switch is open, and that doesn't make sense. Can anyone provide me the correct model? This have been bugging me for a lonnng time. Thanks a lot!!