Day 138: Using Socrative for Short Response Questions

I’ve started using Socrative for assessing students’ short response answers. It serves a couple of purposes. One, I gain valuable insight into what each student does and doesn’t understand. Two, students see each other’s responses, critique them, and see examples of strong responses. Today, one of the questions I posed was from Knight’s College Physics: “The n = 3 state of hydrogen has E3 = -1.51 eV. Why is the energy negative? What is the physical significance of the specific number 1.51 eV?”

The responses clearly demonstrated that there was a substantial number of students who attributed the 1.51 eV as the difference in energy between the ground state and n=3 instead of the difference in energy of the electron between n=3 and infinity.


If I had asked someone to volunteer and answer the question, I never would have realized how few students understood!

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Day 135: Spectra

Today we sought to answer three questions:

  • Why do different elements have different spectra?
  • Why is the absorption spectra a subset of the emission spectra for an element?
  • Why don’t electrons give off energy and spiral into the nucleus?

I also shared how spectra is a critical tool in astronomy so students appreciate this phenomenon.

Day 134: Spectrum of Hydrogen

Today, students started to explore the Bohr model of the hydrogen atom by analyzing the hydrogen spectra. They used a couple of pins and polar graph paper to sight the angle of each spectral line. They then calculated the wavelength and energy of each line. I provided them with the energy levels of the hydrogen atoms without stating the source to see if they could identify the pattern. While most groups accurately measured the spectra, they didn’t immediately connect the energy of the line to the transition between energy levels. We’ll discuss this more tomorrow.

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Day 133: Photoelectric Effect Extended Response

Today, my AP Physics 2 students completed the second half of their photoelectric effect summative lab. Using their data, graph, and analysis from yesterday, they wrote a paragraph-length response to the following prompt:

Do these experiments support the wave model of light or the particle (quantum) model of light? Support your claim with multiple examples based on evidence from the experiments that both support your selected model and refute the other model. You should reference every experiment performed yesterday in your response.

Yesterday, students measured the relationship between stopping potential and light intensity and light frequency. They also measured the relationship between time to charge the capacitor and light intensity.

This prompt was pretty much the same as what I used to include as discussion questions for this lab. However, this year, to help students prepare for the AP Physics 2 exam, I’m taking some of the lab discussion question and making them into paragraph-length response questions that students complete in class with limited time.

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Day 132: Photoelectric Effect Summative Lab

Today, AP Physics 2 students returned from break and completed the first half of the photoelectric effect summative lab. Throughout this lab, they use PASCO’s excellent (and discontinued) h/e apparatus. This first half of the lab has students measure the time to recharge the capacitor for different intensities of light and measure the stopping potential for different frequencies of light. Tonight, they will graph stopping potential versus frequency, interpret the significance of the slope and y-intercept, and solve for h and the work function based on their graph.


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Day 131: Loose Ends and a New Perspective on Electric Motors

Today was the day before spring break. I had originally planned for the AP Physics 2 students to complete the quantitative photoelectric effect lab. However, I realized that a bunch of loose ends had piled up and it would probably take the entire class period to work through them. So, the lab was postponed.

After gathering feedback on yesterday’s field trip, providing feedback on recent exams, and scoring a quiz, I wanted to revisit the electric motors that we built. Students wrote paragraph-length responses explaining how their electric motor worked. I had a “bonus” prompt that asked why the battery connected to the motor would die much faster if the motor was unable to rotate than if it was rotating. Very few students could explain this phenomenon.

Today, I approached the phenomenon from a different perspective. I asked what torques are applied to the armature. Students readily identified the torques to the magnetic force and friction. I then asked if there was an unbalanced torque. Students readily answered that there was. I then ask why their motor didn’t continue to accelerate but, instead, reached a constant rotational velocity. Students didn’t know. At this point, I drew a diagram, reviewed Faraday’s Law of Induction and Lenz’ Law, and demonstrated how the electric motor reacher rotational equilibrium due to the reduced current from the back emf. Next year, I think I’ll try this approach first instead of why the battery dies so fast with a stalled motor.


Day 130: Particle Physics Masterclass at Fermilab!

Today, AP Physics 2 students ventured to Fermilab for the Particle Physics Masterclass! We decided to do the CMS J/Ψ particle Masterclass because event analysis is a good review of charged particles in magnetic fields and the resulting mass plot turns out really well.

The day started with an introduction from two Fermilab physicists and then students broken into pairs to analyze events from CMS. We had some wifi issues; so, we took over the cafeteria where there was better cell reception to create individual hotspots.


Just before lunch, we aggregated our data and produced the mass plot.

J/Psi Mass Plot from 2015 Fermilab Masterclass

Woohoo! We found the J/Ψ!

After lunch, we broken into smaller groups for tours of various parts of Fermilab. Next year, we’ll shorten lunch so we have more time for the tour.