Lerner Physics

We whiteboarded our last photon model of light questions, and the best part of today was the questions. That seems to be my new theme; their questions are so well-crafted and incisive that they should be celebrated. What are the different ways we can define intensity? Why can't an electron just absorb some of the energy of a photon?

And then we moved to special relativity, and the questions kept coming: How is this related to time travel? How much energy would it take to accelerate me to close to the speed of light? What does it mean that "that astronaut" traveled 0.5 seconds into the future?

Now they want to study a lot more special relativity.

We played around with various different gaseous atomic spectra. They are so interesting! Neon looks so red, and the sample marked "air" has so many different lines. We took some artful photos through our cameras, as shown above.

We didn't get quantitative with our observations; I wasn't sure if it was even going to work, but I think next year we can get quantitative. The lines are bright and easy to see, even through cheap diffraction gratings.

We are definitely finishing the year, and, just like last year, when we get to the end of the year, the questions about quantum mechanics are good. Quantum mechanics is weird. I try to explain, and I also try to postpone. I'm not a quantum mechanic!

So, I'm finding the end of the year coming, and I'm actually in a good place. We're going to finish early. We'll have lots of time to review.

I don't think I've ever had that thought before. 

We talked about atomic emission spectra. Of course, I didn't have the tubes ready today (I'll have them tomorrow) so we didn't get to do a lab with it. Still, I could show pictures of the sun's spectrum and its dark lines.

We figured out how to model atomic transitions. The best question was about how this model is similar to and how it different from the model of the photoelectric effect. We talked a lot about the differences of the atoms and what happens to the electron. 

What can we explain with light as a ray, as a wave, and as a particle? Let's whiteboard!

So which one is light, really?

Now I get to blow their minds. None of these models works perfectly. We have to make a kludgy wave-particle hybrid called a photon.

It ends in tears.

But then I made it all better when I said we can energy bar charts (LOL diagrams!) to explain the photoelectric effect. I'll show some whiteboards for that tomorrow.

I need to build a lab for this. But, when I don't have a lab, it always seems that PHeT is there. And I'd use the PHeT simulation for this every year just because it makes it so much easier to visualize.

I always start the photoelectric effect by talking about Einstein's Nobel Prize, and the papers he wrote in 1905. I misspoke today, thinking that Einstein's work on the specific heat of metals was published that year. It wasn't, but his work on Brownian motion was that year instead. That makes that year even more amazing in my opinion.

We then experimented with what changed about the current as we changed the intensity and the wavelength of the incident light. We also investigated what happens when we change the voltage applied across the gap. Our results seemed weird until we came up with the quantum hypothesis.