Light exhibits the properties of wave and particle.
NGSS STANDARD
HS-PS4-3: Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by wave model or a particle model, and that for some situations one model is more useful than the other.
Start the lesson with an overarching question(puzzlement):
How do the wave model and particle model explain the wave behaviors?
How do scientists debate and argue about the nature of the light with the discovery of evidence?
Develop Understanding through Video clips
Andrea McDonough Reviewer: Bedirhan CinarYou look down and see a yellow pencil lying on your desk. Your eyes, and then your brain, are collecting all sorts of information about the pencil: its size, color, shape, distance, and more. But, how exactly does this happen? The ancient Greeks were the first to think more or less scientifically about what light is and how vision works. Some Greek philosophers, including Plato and Pythagoras, thought that light originated in our eyes and that vision happened when little, invisible probes were sent to gather information about far-away objects. It took over a thousand years before the Arab scientist, Alhazen, figured out that the old, Greek theory of light couldn’t be right. In Alhazen’s picture, your eyes don’t send out invisible, intelligence-gathering probes, they simply collect the light that falls into them. Alhazen’s theory accounts for a fact that the Greek’s couldn’t easily explain: why it gets dark sometimes. The idea is that very few objects actually emit their own light. The special, light-emitting objects, like the sun or a lightbulb, are known as sources of light. Most of the things we see, like that pencil on your desk, are simply reflecting light from a source other than producing their own. So, when you look at your pencil, the light that hits your eye actually originated at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye, which is pretty cool when you think about it. But, what exactly is the stuff that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like ripples on the surface of a pond? Scientists in the modern era would spend a couple of hundred years figuring out the answer to this question. Isaac Newton was one of the earliest. Newton believed that light is made up of tiny, atom-like particles, which he called corpuscles. Using this assumption, he was able to explain some properties of light. For example, refraction, which is how a beam of light appears to bend as it passes from air into water. But, in science, even geniuses sometimes get things wrong. In the 19th century, long after Newton died, scientists did a series of experiments that clearly showed that light can’t be made up of tiny, atom-like particles. For one thing, two beams of light that cross paths don’t interact with each other at all. If light were made of tiny, solid balls, then you would expect that some of the particles from Beam A would crash into some of the particles from Beam B.If that happened, the two particles involved in the collision would bounce off in random directions. But, that doesn’t happen. The beams of the light pass right through each other as you can check for yourself with two laser pointers and some chalk dust. For another thing, light makes interference patterns. Interference patterns are the complicated undulations that happen when two wave patterns occupy the same space. They can be seen when two objects disturb the surface of a still pond, and also when two point-like sources of light are placed near each other. Only waves make interference patterns, particles don’t. And, as a bonus, understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow. So, it’s settled then, light is a wave, right? Not so fast! In the 20th century, scientists did experiments that appear to show light acting like a particle. For instance, when you shine light on a metal, the light transfers its energy to the atoms in the metal in discrete packets called quanta. But, we can’t just forget about properties like interference, either. So these quanta of light aren’t at all like the tiny, hard spheres Newton imagined. This result, that light sometimes behaves like a particle and sometimes behaves like a wave, led to a revolutionary new physics theory called quantum mechanics. So, after all, that, let’s go back to the question, “What is light?”Well, light isn’t really like anything we’re used to dealing with in our everyday lives. Sometimes it behaves like a particle and other times it behaves like a wave, but it isn’t exactly like either.
comprehend wave-particle duality in small groups
I divided the whole class into six different groups. Each group would answer one text-based(video) question and one open-ended question. They would also pick a present to prepare for a whole group presentation on behalf of the team.
Group 1:
Is light a particle or a wave? What did the video say?
How would you the toy car and flashlight activity to explain the wave model? (In the previous lesson, we did an activity to compare and contrast the similarities and differences between the scenario when two cars encountered each other and the scenario when two beams of light met each other.)
Group 2:
What was the phenomenon that Newton successfully explained using the claim that light was a corpuscle?
How would you use Newton’s theory to explain reflection?
Group 3:
What evidence disproved Newton’s argument and resulted in a wave model of light?
Group 4:
How did the scientists in the early 20th century explain the phenomenon that when you shine light on a metal, the light transfers energy to the atoms in the metal in discrete packets?
How could you paraphrase it if you describe it to your parents? (Can be in Spanish)
Group 5:
Why did the presenter say, “in science, even geniuses sometimes get things wrong?”
If you had a chance to ask a question to Newton, what would you ask?
Group 6:
Why do you think it took about a century before some scientists successfully challenged Newton’s theory?
What are some measures that we could take to improve the process today?
exit ticket
3-2-1 Exit ticket:
3 – things you learned from other groups’ presentation
2 – things you wanted to learn more about
1 – question you would like to explore more
How does this literacy lesson fit in the 5e model?
I used this lesson as an ENGAGING activity in the 5E model. Students gained an initial impression of the wave model and the particle model. Then, the students would EXPLORE simulations and collect data on wave interference. In the EXPLAIN phase, students would conclude the superposition principle of waves by comparing the behaviors of constructive and destructive interferences. We did not have the time to enact the ELABORATE phase due to school closure, but I envision that students may apply the principles to explain engineering designs such as noise-canceling headsets and create brochures to help their communities to understand the physics behind these devices as their final EVALUATION.
