My Physics Prac plz help!

[MangaFreak]

Can someone please explain how a voltage drop can occur even though the circuit is not closed?
thanks in advance 

[bigtick]

For example, there is a drop in voltage across an open switch.

[appianway]

It makes it easier to think of it as a potential difference.

The potential difference is essentially the difference in potential (or, if you'd like, "voltage") between two points. If you have one end connected to a battery, that end's going to have the potential of the + end of the battery (presuming that no voltage drop occurs across the wires connecting the point to the battery). However, the other point is going to have the potential of the OTHER end of battery, because it's connected to it. Hence the potential difference is the same as the potential of the battery, as each point connected to an end of the battery has the same potential as the battery, and the potential difference is the same as the difference between the two points.