Day 99: Electric Motors

Today, we started building electric motors. I selected a new kit this year since the usual one has been discontinued. I think it is going to work better since it is more hands on and better illustrates the key principles behind the operation of the electric motor. Today’s task was to gather the materials and construct and test the electromagnetic which will eventually be the armature.

These projects are great, and I wish we had more first semester. Many AP Physics 2 students need practice with hammers!

##magnetism

Day 98: AP Physics 2 Paragraph-Length Responses

Today, I was observed and wanted to try something new. Last semester, we focused on lot of explaining physics phenomena and supporting explanations with evidence and physics principles through peer instruction. This semester, I want students to focus on writing paragraph-length responses to prompts similar to those expected on the AP Physics 2 exam. I started by sharing expectations for those paragraph-length responses. I then showed a waveform of a song in Audacity to remind students how when a phone plays a song, it is providing a current, of varying direction and magnitude, to the speaker. I then demonstrated a paper plate speaker.

I then had students write their own response to the prompt “Explain how the speaker converts the electrical signal provided by the phone into the sound that we hear.” Students then worked in groups of three of four to combine their responses into a single response which they typed into a Google document shared with the other groups. We then, as a whole class, critiqued the responses from each of the six groups. The whole lesson took much longer than expected, but I think it was worth the time invested. I shared the lesson with a communication arts teacher later, and it sounds like I’m on the right track. Next time, I’ll talk to the communication arts teacher first!

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Day 97: Quiz and Practice

I was off-campus today for a meeting, and my AP Physics 2 students took a practice quiz and worked some practice problems. When students take practice quizzes from old AP exams, they exchange quizzes and score each others according to the grading rubric. Reportedly, a couple of students didn’t exchange papers and filled in their missing work instead of scoring. I’m not sure why they would do this since the quizzes are for practice and feedback, they don’t directly affect a student’s grade. I may be mislead temporarily, but I won’t next week when we have an exam and, at that point, it will be a bit late for me to help them.

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Day 96: Whiteboarding

Today AP Physics 2 students prepared and presented whiteboards covering a variety of motional emf and electromagnetic induction problems. Many of these required many problem solving steps and integration of concepts we have previously studied. This student ended up being the only one in his group and, on his own, prepared a very clear and concise solution:

Another group made a couple of mistakes and found that the temperature of a muscle during an MRI would increase by 80°C! They weren’t nearly as concerned about this result as I was!

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Day 95: Peer Instruction for Electromagnetic Induction

Today, we spent the entire class period doing peer instruction for electromagnetic induction questions. Properly applying the right-hand rules, Lenz’s Law, and constructing the long chains of reasoning necessary to answer these questions requires a lot of practice. The cumulating question was the following from Knight’s College Physics:

Initially students really struggled to capture this relationship. Only one student sketched the correct graph. Most sketched something along these lines:

After some guiding questions from me and discussions with their peers, several groups produced the proper sketch:

Definitely one of the more challenging questions we’ve discussed!

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Today we discussed the results of yesterday’s Faraday’s Law lab. The new instrumentation amplifiers resulted in much better resolution of the induced emf, which facilitated the data analysis.

While AP Physics 2 is an algebra-based class, a vast majority of my students have taken or are currently taking calculus. So, we took a detour to review the relationship between position vs. time and velocity vs. time graphs from a calculus perspective. I then asked students to sketch a graph of magnetic flux vs. time that corresponds to their graph of induced emf vs. time. While, some struggled to do so, leveraging their understanding of the more familiar concepts of position and velocity helped.

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Today, I was off campus working on the new 6-12 NGSS-aligned science curriculum. I left the Faraday’s Law lab for my AP Physics 2 students. The explored the relationship between flux and the induced emf. Last year, we did this lab with just a voltage probe and the resolution wasn’t great due to the small induced emf. This year, I have Vernier’s instrumentation amplifiers and am hoping for much better results.

Day 92: Hula Hoops, Electromagnetism, and Flux

One of the most helpful visual aids that I employ throughout this unit on electromagnetism is the hula hoop.

I use the hula hoop to demonstrate the application of the right-hand rule for a current-carrying loop generating a magnetic field. I later use the hula hoop to demonstrate flux and how the orientation of the loop changes the flux. I keep it handy throughout the unit!

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Day 91: Electromagnetic Induction Paradigm Lab

Today, we started investigating electromagnetic induction in AP Physics 2. I demonstrated how inserting a magnetic into a solenoid resulted in a current in the solenoid that could be measured with a galvanometer. We then discussed as a class what variables may affect this induced current. The students thought of enough variables such that each of the six groups qualitatively investigated a different variable. After investigation, each group demonstrated their investigation and shared their results with the rest of the class.