Diode Question: need to understand why my approach is wrong

[kostoglotov]

Homework Statement

A screenshot of the problem:

imgur link: https://i.imgur.com/ljtoclm.png

Homework Equations

The Attempt at a Solution

My first attempt at the solution was this:

imgur link: https://i.imgur.com/TJcvOzy.jpg

However, I have access to the worked solution, and it is this:

imgur link: https://i.imgur.com/u0BeWiZ.jpg

I understand the worked solution. What I don't understand is what is wrong in my thinking/understanding so far as my original attempt at the solution goes? Is it not valid to use a Norton Equivalent where I tried to use one? If so, why not?

 

[phinds]

Hard to tell since your first image is illegible (too light). Try it again w/ black ink (and thicker preferably)

 

[NascentOxygen]

In your first case you are calculating the total current from the 9v source. In your second, the calculation is of just the current through the diode.

It seems you may have had your camera set for artificial light, but have taken the shot under sunlight? This causes the extra blue of natural light to dominate, making your white paper appear blue—and losing contrast with the blue ink.