# Day 59: Snell’s Law Quiz

Thursday, 7 November 2013

Gave a short refraction quiz today to all 4 of my classes. 34/58 students earned a perfect score on the quiz that included the index of refraction (n=c/v), Snell’s Law, and critical angles.

The kids are mostly good now about the purpose of quiz corrections, which we do immediately after submitting the online quiz. Kids get the correct answer and must indicate where they went wrong in the problem and show a correct solution if possible. Most of the time, my students can spot their error on their own. The most common errors are setting the problem up wrong or making an algebra mistake in the solution. Below are two examples:

Student made an algebraic error in solving for v. Some kids have trouble when the variable is in the denominator.

Here’s an interesting one: the kid wrote “wrote it wrong” but she actually set the problem up wrong — her ni and nr values were swapped.

Afterward, we moved on to explore why converging and diverging lenses are named the way they are using a laser level and those table-top lenses you can get from scientific supply houses.