Unit 2 · Light, Sound & Information · Week 2
Why can you see through a window but not a wall — and see yourself in a mirror?
The same beam of sunlight hits a window, a painted wall, and a mirror. Three different things happen. Why does light behave so differently depending on the material?
Start here
How we work this lesson (our expectations)
- Observe before you explain
- Use the model, not just the word
- Questions beat quick answers
- Every support is always open — use whatever helps
30-second check-in self-awareness · CASEL
Before we begin, take a quick look around the room. Notice one thing that is shiny, one thing that is transparent (you can see through it), and one thing that is opaque (you cannot see through it). Hold those three observations — you are already doing the science. On a scale of 1 (distracted) to 5 (focused), where is your attention right now? Wherever you are, the lesson moves in small steps, and you can use the Listen button at any time.
Do-Now Quick recall
No looking back. Pull from what you already know — retrieval strengthens memory.
- From Week 1: what is a wave, and what does it carry from place to place?
- From Week 1: if you increase a wave's amplitude, what changes about the energy it carries?
- From Unit 1: when a hand-warmer got warm, the energy didn't disappear — it was transferred. If light hits a dark wall and the wall warms up, where did the light's energy go?
The phenomenon
Stand at a sunny window on a bright day. The glass lets the light pour right through — you can see trees, cars, the whole outside world. Step to the wall beside it: the sunlight stops dead. The wall doesn't let you see through it, and if it's a dark wall, it warms up noticeably in the afternoon sun. Now find a mirror: instead of passing through or stopping, light bounces back at you as a clear image of your own face. Same source of light. Same amount of energy arriving. Three completely different fates — and the only thing that changed is the material. Our question: why does light behave so differently depending on what it hits?
Look at a sunny window. Light goes right through. Look at the wall next to it: light stops and warms it. Look at a mirror: light bounces back and you see yourself. Same light — three different things happen. Why does the material change what happens to the light?
Notice & Wonder. Write one thing you notice about the diagram above and one thing you wonder. Hold your wonder — we are answering it today.
Build it Three fates for every light wave
We'll build the model in three steps. Check your understanding before moving to the next.
Step 1 — Light is a wave, and waves carry energy
You built this last week: light is an electromagnetic wave that travels through space and carries energy. That energy goes somewhere when the wave meets a material — it can't vanish (remember the hand-warmer from Unit 1 — energy is always transferred, never destroyed). The big question is: where exactly does the energy go? The answer depends entirely on the structure of the material the light hits.
Light is a wave that carries energy. When it hits something, the energy must go somewhere — it doesn't disappear. Where it goes depends on the material.
Step 2 — Three possible fates: reflected, absorbed, transmitted
When a light wave meets a material, exactly one of three things (or a combination) happens to its energy:
Reflected: the wave bounces off the surface and travels away in a new direction. A mirror is engineered so almost all the light bounces back in an orderly way — that orderly bounce is what creates a clear image. A white wall scatters light in many directions, which is why it looks bright but shows no image.
Absorbed: the wave's energy is taken in by the particles of the material and converted into a different form of energy — usually thermal (heat) energy. A dark-colored wall absorbs most of the visible light that hits it. The wall's particles start moving faster. You feel that as warmth when you touch it after a sunny day.
Transmitted: the wave passes through the material with most of its energy intact. Glass is structured so that visible light waves can travel through without being blocked or scattered — the particles in glass are arranged in a way that doesn't absorb visible light and doesn't scatter it the way a rough surface would. You can see clearly through it because the wave pattern that reaches your eye still carries the organized information from the scene outside.
Reflected: light bounces off — like a mirror.
Absorbed: light's energy is taken in and becomes heat — like a dark wall warming up.
Transmitted: light passes through — like a window.
Most real materials do a mix of all three. The material's structure decides which one wins.
Step 3 — Structure decides fate (the CCC link)
The crosscutting concept here is Structure & Function: the way a material is built — how its particles are arranged, how smooth or rough its surface is, what it is made of — determines how it interacts with light. A mirror has an ultra-smooth metallic layer; smooth surfaces reflect light in an organized, image-preserving way. Glass has a tightly ordered molecular structure that doesn't absorb visible-light wavelengths. A dark brick wall has a rough surface and particles that are efficient at absorbing visible light's energy. Same incoming light; different material structure; different fate.
The material's structure (how its particles are arranged, how rough its surface is) decides what happens to the light. Smooth metal → reflects. Dark rough wall → absorbs. Clear glass → transmits.
Worked example — tracing one ray's three fates (watch an expert reason)
Setup: a single ray of sunlight leaves the window in your classroom and hits three surfaces in turn.
Fate A — Mirror on the wall: Ray hits the smooth metallic surface. Structure = ordered, smooth. Outcome: wave bounces off at the same angle it came in (angle of incidence = angle of reflection). The wave still carries its energy — you can feel the reflected sunlight as warmth on your face across the room. This is reflection.
Fate B — Dark painted wall: Ray hits the rough, pigmented surface. Structure = rough, pigment particles absorb visible wavelengths. Outcome: wave's energy transfers to the wall's particles — they speed up — the wall warms. Light energy → thermal energy. This is absorption.
Fate C — Glass window: Ray hits the glass panel. Structure = ordered, transparent molecular lattice that doesn't absorb or scatter visible light. Outcome: wave passes through mostly unchanged. This is transmission.
Key point: in every case, energy is conserved. It was never destroyed — it was redirected, converted, or passed on.
Show this as a flow diagram Tier 2 · visual
Draw four boxes in a row: [Light wave approaches] → [Hits material] → three branches: [Reflected: bounces] / [Absorbed: becomes heat] / [Transmitted: passes through]. Label each branch with an example material. Add "energy conserved" as a note at the bottom connecting all three branches.
Your turn Explain the black shirt mystery
Use Claim–Evidence–Reasoning to answer the question below. Choose your response mode — all are equally valid.
The task: On a sunny day, a person wearing a black shirt feels much hotter than a person wearing a silver mirror-finish jacket. Why? Make a claim, give evidence using reflect/absorb/transmit, and explain your reasoning connecting light energy to thermal energy.
I want sentence starters Tier 2 · frames
Claim: The black shirt feels hotter because it ________ most of the sunlight's energy, while the silver jacket ________ it.
Evidence: I know this because absorbed light energy is converted into ________, which makes the particles in the material move ________ and the surface feel ________.
Reasoning: This connects to the worked example because ________ (mention structure and fate).
Word bank: absorbs · reflects · transmits · thermal energy · heat · faster · hotter · structure · surface · particles · converted
Let's back up and make it concrete Tier 3 · re-teach
Analogy: Imagine two sponges. One is black and porous — it soaks up almost every drop of water thrown at it. One is coated in smooth plastic — water bounces right off. Now swap "water" for "light energy." The black shirt is like the first sponge: its dark, rough structure absorbs nearly all the visible light. The silver jacket is like the plastic sponge: its smooth, metallic surface reflects most light away. The shirt's particles end up moving fast (it's hot). The jacket's particles barely change (it stays cooler).
Fill in: The black shirt is hot because it absorbs light, which turns into ________ energy. The silver jacket is cooler because it ________ most of the light away, so less energy is transferred to ________.
Try saying the complete answer out loud once before you write it.
Push my thinking Extension
Most real materials reflect some light, absorb some, and transmit some. A red apple, for example, reflects red wavelengths but absorbs most other colors. Design a brief investigation: how would you use a thermometer, two cups of water, and colored paper to compare how much thermal energy different colors absorb from the same light source? Write a testable question, a prediction, and your procedure in three steps.
Check yourself Did it click?
- define reflection, absorption, and transmission and give an example of each;
- explain that absorbed light becomes thermal energy (connecting to Unit 1);
- use the idea of material structure to explain why different objects behave differently in light.
A student shines a flashlight at a smooth metal mirror and then at a dark-gray concrete wall. The mirror looks bright and reflects a clear image. The concrete wall looks dull and warms up after a few minutes. What best explains the difference?
Re-teach: light is never created or destroyed — only redirected or converted Tier 3
This connects directly to Unit 1: energy is never created from nothing and never destroyed — it is always transferred or converted. A mirror does not make new light. It bounces the incoming wave away with most of its energy intact — this is reflection. A dark wall does not destroy the light. Its particles absorb the wave's energy and it becomes thermal (heat) energy — this is absorption. The energy just changed form. Go back to option B and notice how it describes the structure of each material — that structure is what determines the fate of the energy.
Reflect, then show what you know
Reflection metacognition + responsible decision-making · CASEL
Think about the three fates of light you learned today — reflected, absorbed, transmitted. Which one was the hardest to picture? What is one thing you could do (open a support, re-read a step, draw a diagram) to make it click before the next class? Naming that next step is what scientists do after they hit a confusing idea.
Exit ticket — answer in your notebook or on paper.
- New In your own words, what does it mean for light to be absorbed? Name one material that is a strong absorber of visible light.
- New Explain why a smooth mirror produces a clear image but a white painted wall does not, even though both reflect light.
- Spiral · Week 1 A wave transfers energy from place to place. When light is absorbed by a dark wall, what specific form does the wall's energy increase in? How does this relate to amplitude from Week 1?
- Spiral · Unit 1 In Unit 1 you learned that energy is never destroyed — only transferred or converted. Use that principle to explain what happens to the energy in a beam of light that hits a black surface. Be specific: transferred to what? Converted to what form?
- Transfer · Preview Week 3 We said light can be reflected, absorbed, or transmitted. Do you think sound waves also behave this way when they hit different materials? Give one piece of reasoning for your prediction — and explain why there is no sound in outer space (hint: what does sound need that light does not?).
Educator panel — facilitation, accommodations, answer key
At a glance
Standard: NGSS MS-PS4-2 — Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials. 3D: SEP Developing & Using Models · DCI PS4.B Electromagnetic Radiation & PS3.A Energy · CCC Structure & Function and Energy & Matter. Throughlines: builds on Week 1's wave-energy model; reinforces Unit 1's energy-conservation principle; connects to Week 3 (sound also reflects, absorbs, transmits) and to the unit's driving question about information transmission.
Materials (optional; fully digital-capable): flashlight or window sunlight; mirror, dark cloth, and glass pane to demonstrate (or the embedded SVG diagram). No lab required.
Facilitation arc (Rosenshine)
- Launch the phenomenon — three objects, same light source, three fates — before naming any vocabulary (3 min).
- Do-Now retrieval while you take attendance; cold-call item 3 (energy conservation link to Unit 1) (4 min).
- Build Steps 1–3 with the worked example; pause and check for understanding after Step 2 using the diagram (15 min).
- Differentiated CER practice — circulate; note which tier supports students open (12 min).
- Self-check + branching re-teach for any A/C responders (5 min).
- Brain break, reflection, exit ticket (10 min).
Anticipated misconceptions
- "A mirror creates its own light." — Mirrors only redirect incoming waves; they produce no new energy. Route to re-teach panel.
- "Absorbed light is destroyed." — Absorption converts light energy to thermal energy; it is never destroyed. This is the core Unit 1 throughline.
- "Transmission = reflection in the other direction." — Transmitted light passes through the material; reflected light bounces back on the same side.
IEP / 504 accommodation cards
Common accommodations mapped to this lesson
| Accommodation | How it's already built in / what to do |
|---|---|
| Text read aloud | Every core passage has a Listen button (TTS via Web Speech API); simplified toggle shortens it. |
| Reduced reading load | "Reading: Simplified" swaps in shorter plain-language text across all passages. |
| Chunking / extended time | Lesson is in three numbered steps; progress saves to localStorage — learners can stop and resume. |
| Sentence frames / word bank | Tier-2 panel under the CER task provides frames and a 11-word word bank. |
| Concrete / analogical re-teach | Tier-3 "two sponges" analogy plus a cloze fill-in under the practice task. |
| Alternative response mode | Learners may draw a labeled diagram, speak/record, or write the CER — all accepted. |
| Behavior / focus (504, ADHD) | Named expectations (PBIS), the 30-sec observation check-in, and a built-in movement brain break. |
| Multilingual / EL | Simplified text, the SVG diagram carries meaning without text, word bank, and home-language reflection is always allowed. |
Exit ticket answer key
- Absorbed means the material takes in the wave's energy and converts it — usually to thermal energy (heat). Strong absorbers: dark-colored materials, matte/rough surfaces, black asphalt, dark cloth.
- Both reflect light, but a mirror's ultra-smooth metallic surface reflects rays in an organized, angle-preserving way — the reflected rays still carry the pattern of the original image. A painted wall's rough surface scatters light in many random directions, so no coherent image forms, even though total light energy is still redirected.
- The light's energy increases the wall's thermal (heat) energy — the wall's particles move faster. Amplitude (Week 1) describes the energy a wave carries; a higher-amplitude light wave would carry more energy to be absorbed, causing a greater temperature increase. The absorbed energy equals the wave energy that arrived (conservation).
- The light energy is transferred to the black surface's particles (absorbed by them) and converted to thermal energy (heat). No energy is lost — it changed form from electromagnetic wave energy to the kinetic energy of moving particles (heat). This matches the Unit 1 principle: energy is always conserved, never destroyed.
- Accept any prediction with reasoning. Strong answer: yes, sound also reflects (echo off a wall), absorbs (soft foam soaks up sound), and transmits (you hear a conversation through a closed door). Sound cannot travel through outer space because sound is a mechanical wave — it needs particles (a medium) to transfer its energy from place to place. Light is an electromagnetic wave and needs no medium, so it travels freely through the vacuum of space while sound cannot.
Why it's designed this way
Phenomenon-first (NRC 2012 / Reiser et al. 2021) surfaces the three-fate contrast before vocabulary is introduced. The worked example fades support to reduce cognitive load (Sweller); Tier-2 sentence frames and Tier-3 analogy are additive on the same goal, never a reduced goal (UDL 3.0 / MTSS). The Do-Now and exit ticket items 3–4 deliberately pull Week 1 (wave-energy model) and Unit 1 (energy conservation) — this interleaved retrieval strengthens long-term retention and makes the crosscutting concept visible (Roediger & Karpicke; Rohrer). Exit ticket item 5 (sound-in-space transfer) previews Week 3 and the unit driving question about information transmission, planting a productive puzzle (Black & Wiliam formative loop). The brain break uses the learner's own hand as a live demonstration of absorbed vs. transmitted light, embedding the CCC Structure & Function in a physical, culturally-neutral experience (PBIS; Hammond 2015).