Diode Circuit Problem

dashkin111

1. The problem statement, all variables and given/known data
See attachment


2. Relevant equations
We are to assume the voltage drop across diodes is .7v (don't use the diode equation!).


3. The attempt at a solution

I first was assuming that both diodes were "on". Then my work is as follows:

V1 is the voltage directly above diode D1 (the left most diode)...



[tex]I+ \frac{V_{1}-.7-(-5)}{5k\Omega}=\frac{5-V_{1}}{10k\Omega}[/tex]

[tex]I+ \frac{.7-.7+5}{5k\Omega}=\frac{5-.7}{10k\Omega}[/tex]

[tex]I=-.57mA[/tex]

Now since I is negative, one of my assumptions is wrong? So now I assume the rightmost one is "off" (D2).


So.. then
Solving for I
[tex]I = \frac{5-.7}{10k\Omega}[/tex]

[tex]I = .43 mA[/tex]

Solving for V
Well.. since theres no current, v=-5?



Am I approaching this correctly?

Attached Thumbnails

 

Gokul43201

You're on your way. In this second case, what would be the value of V1? Does this agree with your assumption?