Next Generation Science Standards

Performance Expectation

Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other.

• Clarification Statement: Emphasis is on how the experimental evidence supports the claim and how a theory is generally modified in light of new evidence. Examples of a phenomenon could include resonance, interference, diffraction, and photoelectric effect.
• Assessment Boundary: Assessment does not include using quantum theory.

Potay-to, potah-to. Tomay-to, tomah-to. Wave, particle.

In this performance expectation, students will explore the two different models we use to describe light: the wave model and the particle model. They'll evaluate the evidence supporting each model and why different models are used to describe light in different scenarios. When they're done, they'll see that light can't be pinned down so easily.

Wave or particle? Particle or wave? Try out both with some of these activity ideas:

• Ask students what light is made of and have them do a Think-Pair-Share. First, have them brainstorm ideas individually, and then have them share their ideas with a partner. Finally, discuss ideas as a class and introduce the wave and particle models.
• Divide the class into two sides and hold a debate. One side will argue that light is a wave, while the other side will argue that it is a particle. Slinging evidence, claims, and scientific reasoning is encouraged. Slinging backpacks and pencils is not.
• Provide small groups of students with several cards describing different "tricks" light can do, such as reflection, refraction, or diffraction. Have them discuss which light model best accounts for the way light behaves in each scenario. Discuss as a class when they are finished.

Disciplinary Core Ideas

PS4.A – Wave Properties: [From the 3–5 grade band endpoints] Waves can add or cancel one another as they cross, depending on their relative phase (i.e., relative position of peaks and troughs of the waves), but they emerge unaffected by each other. (Boundary: The discussion at this grade level is qualitative only; it can be based on the fact that two different sounds can pass a location in different directions without getting mixed up)

We're taking it back. Waaaaay back. Bust out your Trapper Keeper and scented markers because we're going back to elementary school. Here, students learned that when waves cross paths, all kinds of shenanigans take place, but the waves emerge unchanged. And that was pretty much the extent of it.

For this performance expectation, they're going to need to learn a few more details on those shenanigans. Like, for example, that resonance involves waves with matching peaks and troughs adding together to create a greater amplitude.

They should also know that interference happens when two waves meet while passing through the same medium. No, this is not the beginning of a romantic comedy. Either the waves will be a perfect match of peaks and troughs and the amplitude will increase, or the peak of one wave will match the trough of the other wave and they'll cancel each other out. Maybe this is like a romantic comedy…

Then there's diffraction, which is basically when waves change direction to move around an obstacle or through a small opening. It's sort of like when you're standing on the beach and waves hit your ankles. The water changes direction to move around you and then proceeds on its original path.

Lastly, there's the photoelectric effect. Here, they basically need to know that waves of a high enough frequency can dislodge electrons from certain metals. This comes in pretty handy when we're trying to turn sunlight into electricity (or describe why electromagnetic radiation acts like a particle).

Let's be honest, your students probably won't remember what they learned about waves in the third grade. They can barely remember what you said six minutes ago. Thus, you may need to do a little re-teaching of these concepts to refresh their memories. Also, we know it's the fun part, but don't go into the quantum stuff unless you want to see their eyes glaze over faster than a Krispy Kreme.

PS4.B – Electromagnetic Radiation: Electromagnetic radiation (e.g., radio, microwaves, light) can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features.

Trying to describe electromagnetic radiation is sort of like trying to describe what the number purple smells like. After much deliberation, scientists decided that it just can't be shoved in a little box and slapped with a label maker. Thus, we describe electromagnetic radiation using two models.

The first model that students should know about is the wave model. Captain Obvious named it, so you can guess that this model describes EM radiation as a wave. EM radiation has the same structure as any other wave, and it's made up of fluctuating electric or magnetic fields. As such, the wave model is useful for explaining wave tricks like diffraction.

Then we've got the particle model. The particle model describes EM radiation as a bunch of little particles (shocker!) called photons. Photons are tiny packets of energy that are steadily emitted from a source, sort of like particles of spray paint from a can. This model is particularly useful for explaining how light behaves when it is reflected or refracted or causes the photoelectric effect.

Your students aren't going to like this semi-ambiguous way of describing light, mostly because it requires them to use the deeper portions of their brain to think. That's okay. You're not here to win a popularity contest.

Once they understand how both EM radiation and waves behave, they should be able to understand why waves make sense to describe some of the properties of EM radiation and why particles make sense to describe others. This is a great opportunity for students to experience some peer teaching, so group them according to understanding and watch the light bulbs turn on above their heads.

Science and Engineering Practices

Engaging in Argument from Evidence: Evaluate the claims, evidence, and reasoning behind currently accepted explanations or solutions to determine the merits of arguments.

It's easy for students to read something in their textbook or listen to you lecture about it and just assume that it's true. However, scientists like to assume someone is telling the truth about as much as they like filing their nails on a chalkboard.

In this performance expectation, students should be able to look at the arguments for describing light as a wave or as a particle and determine whether those arguments are valid. Yes, this will require some research and a healthy dose of skepticism. No, it won't hurt them.

Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena: A scientific theory is a substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment and the science community validates each theory before it is accepted. If new evidence is discovered that the theory does not accommodate, the theory is generally modified in light of this new evidence.

Students should consider theories to be written in erasable pen. Theories aren't as flimsy as hypotheses, because they've been tested a gazillion times in a gazillion different ways, and they always come back with the same result (scientists like this).

They can't be written in Sharpie, however, because there's still the possibility that somewhere out there someone can perform an experiment to disprove the theory, or at least cause us to expand and improve on it. When and if this happens, scientists work to collect more evidence and will eventually modify the theory to accommodate the new information that has come to light.

For now, our wave and particle theories of how light functions are the best ideas we've got. They've been tested, and tested, and tested some more, so until someone comes up with something better that's supported by a whole lot of evidence, we're going to stick with it. As an added bonus, a lot of really smart folks worked on developing our current understanding of EM radiation, including some guy named Einstein. That always impresses students.

Crosscutting Concepts

Systems and System Models: Models (e.g., physical, mathematical, computer models) can be used to simulate systems and interactions—including energy, matter, and information flows—within and between systems at different scales.

Models are a scientist's best friend. And no, we're not talking about swimsuit models. Sorry for the confusion; we're talking about models of the physical, mathematical, and computer variety. Ah yes, now it all makes sense.

Students should understand that much of what scientists study can't be observed directly. Scientists don't let this get them down, though. Instead they just whip up a model and use that to help them understand a phenomenon.

This is exactly what they've done with EM radiation. We can't "see" what it's made of, so scientists came up with a wave model and a particle model to help them understand the way it behaves. We may not find these models in the next Sports Illustrated Swimsuit Edition, but they're still extremely useful.