Question

I have the circuit that is shown in the following picture http://i.imgur.com/mcNe4b4.jpg. Currently I'm not sure that I understand two things about it. Firstly how do I know the polarity over the resistance. Secondly they ask what the power is for each circuit element. I found that the current over the resistance is 2A and thus Pr = 20 W, Pv=20 W. Thus the current source have to be -40W, but given the relation that P=v(t)i(t) I get -(2*10)=-20 W.

Answer 1

For the first question is it, perhaps because the current is moving clock-wise and thus there is a voltage drop over the resistance which determines the voltage polarity?

Answer 2

Is the element on the left a current source, or just an ammeter in the circuit measuring 2 amps?

Answer 3

I am thinking, that it is an ammeter, and the current is electron flow rather than conventional current direction.
The power in the resistor is as you say 20 watts (I^2R) and the power provided by the battery is also 20 watts (EI) and their is negligible voltage drop across the ammeter and the power used by the ammeter can be ignored.