Circuit Troubleshooting: Finding Correct States of Diodes

[seang]

Today in class we learned about diodes. Our prof explained to us that the only manual way to find the correct states of the diodes is guess and check. Each time, we ended with one correct circuit; that is Kirchoff's laws coincided with the diode constraints.

Now I'm doing this circuit on my own, and I'm finding that there are 2 combinations which fulfill Kirchoff's laws. Is this possible? or must I be making a mistake somewhere?

The circuit is simple really. DC sources resistors and diodes.

 

[berkeman]

As long as you don't put so large a reverse voltage across the diode to break it down, it will only conduct in the forward direction, when current flows from anode to cathode. It's best to think of diodes in terms of the diode equation:

http://en.wikipedia.org/wiki/Ideal_diode_equation

 

[dlgoff]

Take a look at the http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Diodes/Diode1.html" and see if it helps answer your question.

Regards