Questions Regarding Circuits and Electricity

[AnomalyCoder]

Well I'm having a quiz coming up on Electricity/Circuits, and I want to get an A on it .
However, regardless of the coursework I went through, I still have a few questions.*The Voltometer:
http://img242.imageshack.us/img242/5664/circuitcopy.jpg

It displays a voltage of 31.81 for the resistor in the image.
How would one generate that number?

*What is the difference between potential difference and voltage drop?

And what would be the voltage drop from point a to b in the image below:
http://img716.imageshack.us/img716/3595/voltagedrop.jpg
(Incomplete circuit)

Also, I was wondering if anyone had any good resources to study from. (Extra worksheets, etc)

 

[Mindscrape]

The difference between potential difference and voltage drop is nothing, other than a sign change. Nobody, not even physicists, ever talks about the "potential difference" in a circuit, it's always voltages. Voltage drop is how much the potential difference drops. Circuits, by convention, are always defined with respect to a positive flow of current.

In your second picture, you have an open circuit, which gives a voltage 9V.