Direction of current in the figure?

[ehabmozart]

Direction of current in the figure??

Homework Statement

What must the emf in the figure be in order for the current through the 7.00-ohm resistor to be 1.76A? Each emf source has negligible internal resistance. Figure

http://i239.photobucket.com/albums/ff92/anakris_24/yf_Figure_26_51.jpg

Homework Equations

Kirrchoff's Laws

The Attempt at a Solution

I know well how to use the laws but my problem here is in determining the direction of current through the 7Ω resistor. Is it up or down and why? ... In the manual it say it goes down due to polarity of the battery.. But it can actually go out of battery 1(left) and battery two?

 

[gneill]

Try applying superposition. What direction does the current flow through the 7 Ω resistor due to each source when taken individually?

 

[CWatters]

In the manual it say it goes down due to polarity of the battery.. But it can actually go out of battery 1(left) and battery two?

I don't understand your explanation. Even if the current flows out of the 24V battery into the ε battery the top end of the 7R will still be +ve wrt the bottom end.

If ε is +ve then I can't see how the current can ever flow upwards through the 7R.

Edit: It would be bad practice to show ε as -ve with the battery drawn that way around. It would be ok to show a voltage source with the arrow pointing upwards and ε marked as -ve but that's not what you have here.

 

[CWatters]

How about solving it twice. Once assuming the current flow down through the 7R and one assuming it flow up through the 7R. What do you get?