Waves, Sound, and Light
Every question in this unit is really testing one idea from three different angles: waves carry energy, not matter, and what a wave is (mechanical or electromagnetic) decides everything else about how it behaves. Sound needs a medium and squeezes it into compressions; light needs no medium and gets bent, split, or bounced depending on what it hits. Once you can sort a question into 'this is about the wave's properties' vs 'this is about what happens when the wave meets a surface,' most of the marks in this bank become predictable.
Overview: How This Unit Fits Together
The big split: mechanical vs electromagnetic
A wave is a disturbance that transfers energy from one place to another without transferring matter. This unit splits into two wave families that behave differently at every single point of comparison. Sound is a mechanical wave — it needs particles (a medium) to bump into each other, so it cannot travel through a vacuum. Light is an electromagnetic wave — it needs no medium at all, which is exactly why sunlight reaches Earth across empty space.
- Sound is longitudinal — particles vibrate parallel to the direction the wave travels, creating compressions and rarefactions.
- Light (and all EM waves) is transverse — the oscillation is perpendicular to the direction of travel, which is why it can be polarised and sound cannot.
- Both families obey the same core relationship between speed, frequency and wavelength — that single equation reappears in the sound section and the properties-of-waves section.
- What happens at a boundary (a prism surface, a mirror, an eardrum) depends on whether you're asking about reflection, refraction, or absorption — these three get mixed up constantly in exam answers.
The shape of the chapter
Command terms this bank actually uses
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Identify | Give a name, term, or single fact — no explanation needed and none rewarded. | Knowing & Understanding | One-word or short-phrase answers earn full marks; a full sentence wastes time, not marks. |
| State | A brief, precise statement with no justification required. | Knowing & Understanding | Same weight as Identify — don't over-explain. |
| Describe | Give the details of what happens, in sequence, without saying why. | Knowing & Understanding | Marks go to accurately naming the process (e.g. refraction, dispersion) even without a full causal explanation. |
| Explain | Give reasons or a mechanism — the 'why', not just the 'what'. | Knowing & Understanding / Analysing | A Describe-level answer to an Explain question loses the reasoning mark even if every fact stated is correct. |
| Compare | Give both similarities AND differences between two things. | Analysing | Naming only differences (or only similarities) caps you at half the available marks. |
| Suggest | Propose a plausible explanation using scientific reasoning, even without being told the exact answer. | Analysing | Any reasonable, scientifically consistent idea earns credit — you don't need 'the' textbook answer. |
Key point
Overview