Why is my solution for real diode analysis wrong?

[theBEAST]

Homework Statement

Homework Equations

I=I_se^(V/V_T)

The Attempt at a Solution

The solution I got is wrong. Does anyone know why?

Here is my attempt, the image was too large for this forum so here is the link:
http://i.imgur.com/4tuGxdO.jpg

 

[ehild]

You ignored V_T in the exponent.

ehild

 

[theBEAST]

You ignored V_T in the exponent.

ehild

Isn't the V_T value the same (approximately 0.025V at room temperature)?

 

[gneill]

Isn't the V_T value the same (approximately 0.025V at room temperature)?

The approximation is just that, an approximation. It is a good "typical" value for run-of-the-mill diodes. The actual value for a given diode depends upon the details of the diode doping. You should determine its true value for this problem.

 

[ehild]

Isn't the V_T value the same (approximately 0.025V at room temperature)?

Even in case it is, I1/I2 = e^(V1-V2)/V_T

ehild

 

[mezarashi]

You may need to run a few simultaneous equations. Here's my suggestion: Use the generic information provided to solve for Is and VT before proceeding further. Then from there you can solve for R using the fact that both sides of the circuit must equate 10mA.