# Day 52: Little Notes to Myself

Tuesday, 29 October 2013

Note to my future self.

Kinda boring photo-wise day in class — working on classwork.

But, I did find a mistake in my problem set. What do you do when, in the moment, you realize a problem is worded badly or flat out impossible to solve? I usually provide a verbal fix to the class in the form of “hey, guys, what I meant to say was…” Ahhh, the challenges of writing problem sets and not proofing or solving them in advance.

Remembering to fix my mistakes before reusing the problem set is tough. So, I’ve started leaving notes to myself on top of the document so I can remember to fix the mistake next year. It’s almost always faster than fixing the problem right now.

My students spent today finishing the classwork that included this problem (bad wording and all):

3. Two plane mirrors are taped together to form a right angle. This mirrored corner is set on a table so that the mirrors are in two vertical planes. A horizontal ray of light is directed toward the mirrored corner so that it strikes first one mirror and then the other.

a. Draw a diagram to show the incident and reflected rays.

b. Prove mathematically that any incident ray that strikes anywhere in the mirrored corner is reflected back, parallel to the incident ray.