Solution:

V_{T} = emf – iR (general)

In this case, V_{T} = 40V, when considering V_{T} = V_{ab} = V_{b} – V_{a}

V_{T} = V_{ext} – 28V – i(1.5Ω)

Now, I’m not entirely certain of where I went wrong, but don’t seem to know much about the current besides that it is going from a to b in the cell.

The solution shows the answer is 8.0A but I can only get that if I do 0 = 40V – 28V – i(1.5Ω) but I don’t quite see how you can apply the 40V inside (using Kirchoff’s loop rule) if that’s the terminal voltage instead of the applied voltage from an external source. Any clarification on what I am doing wrong or what I should do, and clarification on V_{T} would be helpful.

This is what I quickly used as a reference: http://ift.tt/1maA6nM

http://ift.tt/QbJj45