Waves & Different Materials

Pupils aged 12–13 build and wield the three-fates model: at any boundary a wave is reflected, absorbed, or transmitted (usually a split of all three), with absorbed energy conserved as heat. The load-bearing idea is that the outcome depends on the MATERIAL and the WAVE'S FREQUENCY TOGETHER, not either alone. Learners test a material×band grid, then transfer the model to three contexts — colour as selective reflection, sight, and band-matched communication technologies — and confront the X-ray puzzle that breaks the intuitive 'big waves slip through' story.

• 'Big waves slip through, small waves are blocked' (size-only) — a useful stepping stone but incomplete and misleading; it cannot explain glass vs brick vs metal, and the X‑ray puzzle (short wavelength, yet transmitted through flesh) breaks it outright. The real determinant is how the material's electrons respond to that frequency.
• 'Transmission only happens through transparent things / if I can't see through it, nothing gets through' — but a brick wall is opaque to light yet transparent to radio. Transparency is wavelength-specific, not a blanket property.
• Treating reflect/absorb/transmit as a FIXED, single property of a material ('mirrors reflect, black things absorb, glass transmits') rather than depending on the wave's frequency too — the same glass transmits visible, absorbs UV, and transmits radio.
• 'Absorbed light just disappears / is destroyed' — absorbed energy is conserved and becomes heat (thermal/infra-red); this is the greenhouse and dark-clothes effect.
• Colour is an innate property of an object regardless of lighting (carried from the colour topic) — colour is the set of frequencies REFLECTED/transmitted, so it depends on the illuminating light; a red object under blue light looks black.
• Not seeing WHY different comms bands are chosen — pupils think the choice is arbitrary rather than driven by which fate the band undergoes in air/walls/fibre (radio penetrates and travels far; visible light is trapped by walls but guided perfectly down a fibre).
• 'Radio always passes, light never does' as an absolute — penetration depends on material and thickness (metal blocks radio; metres of rock attenuate it), and glass lets light straight through.

• A single-boundary 'three fates' diagram: one incoming beam splitting into a reflected ray, an absorbed portion (shown warming the slab / glowing infra-red), and a transmitted ray — with an energy bar showing the three shares summing to the input.
• A material×band interaction GRID/table: rows = materials (glass, brick, metal, water, skin, black card), columns = EM bands (radio, microwave, infrared, visible, UV, X‑ray); each cell marked mostly Reflect / Absorb / Transmit — the organiser that makes 'material AND frequency together' visible at a glance.
• Colour-as-selective-reflection panel (reused from White Light & Colour): white light in, absorbed frequencies greyed out, reflected frequency to the eye — positioned as the visible-light cell of the same grid.
• Real-world application cards, each anchored to a band and its fate: Wi‑Fi/radio through a wall, greenhouse/thermal camera (infrared absorbed → warmth), fibre-optic cable (visible/IR transmitted along glass), sunglasses/sunscreen (UV absorbed/reflected).
• The X‑ray-puzzle contrast strip: radio (long λ) passes, visible (mid) blocked, X‑ray (short λ) passes — laid on a wavelength axis to visibly defeat the 'smaller = more blocked' story.

• Lead with a familiar phenomenon that the reflect/absorb/transmit model then EXPLAINS: Wi‑Fi/radio reaches the basement but room light does not escape; a greenhouse warms in sun; a thermal camera sees a warm body in the dark; sunglasses cut glare. The phenomenon first, the model as the payoff (matches the KS3 aim of relating explanations to everyday phenomena).
• Teach the clean three-fates model — at a boundary a wave is REFLECTED, ABSORBED, or TRANSMITTED, usually a split of all three — and make it quantitative-qualitative with an energy bar so the three portions visibly sum to the incoming energy (nothing lost).
• Hammer energy conservation on the ABSORBED share: absorbed radiation is not destroyed, it warms the material (EM → thermal/infra-red). This is why dark clothes get hot and a greenhouse heats up.
• Make the CENTRAL point that outcome depends on MATERIAL and FREQUENCY TOGETHER, not either alone: build a material×band grid and predict-then-test every cell, so pupils meet the SAME material behaving differently to different waves (glass: transmits visible, absorbs UV, transmits radio).
• Fold colour in as the visible-light special case — an object's colour is the frequencies it reflects/transmits rather than absorbs; black = absorbs all visible (reuse and connect to the White Light & Colour lesson rather than re-teaching from scratch).
• Connect to communication technology by matching band-to-job with the REASON: radio for through-walls/long-range broadcast, the microwave atmospheric 'window' for satellite links, infrared for short-range line-of-sight (remotes, fibre), visible light for fibre optics.
• Use the intuitive 'big waves slip through, small waves blocked' analogy as a deliberate STEPPING STONE, then break it with the X‑ray puzzle (very short wavelength yet passes through flesh) to show a size-only account fails and it is really about how the material's electrons respond — a strong stretch prompt toward KS4/photon-energy ideas.