Find the voltage between A and B in the circuit below:
Don't know really, except for Ohm's law and Kirchhoff's laws, in some combination.
3. The Attempt at a Solution (rather the solution that the key gives, which I don't understand)
(12-6)/150 = 0.04 Ampere
U_AB = 6 V + 0.04*50 = 8.0 V
The main problem I have here, is that I get confused when there are two batteries in one circuit. So:
a) Is there any standard approach to deal with serveral batteries, e.g. build some sort of battery equivalent, like you do when you have several resistors?
b) They seem to substract one of the battery's voltages from the other. Why's that? On one hand, you can see that one battery is "driving" the current in opposite direction to the other. But on the other hand, you could say that in the upper part of the circuit, the batteries' plus terminals form one common conductor, so it ought to be 12+6=18 V.
c) Then they seem to treat the resistors like they were in series. Well, in the left circle of the diagram, you can say they are in series, so maybe I'll agree with that.
d) Okey, now you have the current I. But now they do 6 V + 0.04*50 to get U_AB. Strange... Normally, you do U - RI to get the potential left...