Day 51: A Repetition

Friday, 25 October 2013

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Check out how this kid did the problem correctly…except for the fact he/she thinks Superman’s using his laser vision (incident rays coming from his eyes).

I’m finding this whole 180 thing a little tough on days where my schedule basically repeats the previous day. Today, I finished giving quizzes to my class. The front of the page was a mirror maze, while the back asked the students to hang a mirror on the wall for Superman to admire himself.


Day 50: Mirror Maze Quiz

Thursday, 24 October 2013

The mirror maze quiz question builds on work done in the lab. Logistics: give students a protractor and paper only. Ask them to bring you the paper when they’ve completed the problem. You set up the mirrors on their indicated lines and turn on the laser. My purple marks on each page shows the actual path the laser took through the bullseye. Here’s an assortment of student work on the mirror maze problem.

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This kid gets the law of reflection and provided a well-labeled diagram.

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Another excellent solution, though due to several inaccurate measurements, is a little off-target.

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This student doesn’t understand the problem statement and instead assumes two parallel mirrors are necessary.

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This is what happens when you mis-apply the law of reflection — look at the reflection from the lower mirror.

Have I mentioned this is my favorite quiz of the year?

Day 48: Mirror Maze & Protractors

Tuesday, 22 October 2013

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An example of the mirror maze. There’s a starting line for a laser beam to be brought in later, a wall obstacle, and a target at the end. This is about half-way through my time working with a small group of kids. I don’t worry them about most labels till the end.

I worked with small groups of kids to practice building a mirror maze, which I’ve told them is on the quiz Thursday. They know this much: they’ll be provided a protractor, paper, and pencil. The objective is to draw mirror placements that will reflect a laser beam from a starting arrow, around an obstacle, and to a finishing target.

In the two years I’ve taught with this particular assignment, it’s amazing how some kids are so freakin’ ingenious with building the maze efficiently.

More amazing to me, however, are the high school freshmen (aged 14 and 15) who cannot measure an angle with a protractor. Most of my time today, in fact, was devoted not to the finer points of accurate measurements but to placing and reading a protractor. After the frustrations in class, I turned to Twitter for advice and my friends delivered:

  • Bridget Dunbar (@BridgetDunbar) told me she used to highlight the bottom ray and put small dot stickers on the protractor plus one on each side next two the scale; the highlighted ray points to the sticker with the scale you’re supposed to read.
  • Jennifer Silverman (@jensilvermath) suggested I cover the second set of angle measures so kids aren’t confused by seeing the supplement to their angle on the protractor.
  • John Stevens (@Jstevens009) found this game to practice protractor use.
  • And John Burk (@occam98) shared a protractor video he made.

Many thanks for the thoughtful advice!

Day 47: Ray Tracing

Monday, 21 October 2013


Above, my twist on the daily agenda is how I keep track of “did I do this with your class?”. Checklists on the board of major topics, assignments, and upcoming quizzes. I get extra mileage out of this scheme because if I forget, some enterprising kid in the class will ask “hey, how do we ray trace for convex mirrors?” or something.


Today, we practiced ray racing in all 4 classes. The kids are working off this handy notes sheet I made with real spherical mirrors drawn to scale. Afterward, the kids move on to the classwork.

What was the warmup in 7th period today?

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Day 45: Flat Mirror Warmup & Spherical Mirror Play

Thursday, 17 October 2013

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The big news today is the assembly we had that was devoted to robotics. Our goal was to gain student fans and I’d say our captains nailed it. Watch the recording here.

I had to teach a little physics today, too.

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I love the way this section is working out this year. We learned ray tracing in a spherical mirror and the mirror equation on the same day. I had the kids work out the equation for the image of the smiley face above [get the Word version]. They computed an image distance then used ray tracing to check their answer.

Everything goes great until this one:

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“Ms. H-G, why is the image distance negative?”

When I tell them the other images were real and this one is virtual, they want to know what the difference is. I tell them real images can be projected onto a sheet of paper and virtual ones can’t. They demand proof, so I grab the concave mirror, a model, and several students with flashlights. We held a sheet of paper where the real image formed and saw our model’s face on the page. Of course, this kind of thing doesn’t photograph well, so here’s an example I found online.

What was the warmup in 4th period?

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We also watched a clip from Minds of Our Own (thanks, Frank!) starting around 6:30 about how backing away from a mirror doesn’t allow you to see more of yourself.

Day 44: PSAT

Wednesday, 16 October 2013

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From 9am to noon, I administered the PSAT to my advisement group. Afterward, two of my advisees and their parents came back for conferences with me. We talked about college tours, math class, community service, and not getting enough sleep. The picture is of the “Circle of Friendship” I created to facilitate the conferences.