Light and sound
Light and sound are both waves, but they differ in nature: light is a transverse electromagnetic wave that travels through a vacuum; sound is a longitudinal mechanical wave that needs a medium.
Refraction at a boundary
When light passes from one medium to another it changes speed. If it slows down (e.g. air → glass), it bends towards the normal. If it speeds up (glass → air), it bends away from the normal.
Always draw the normal as a dashed line at 90° to the surface and measure angles from it, not from the surface.
Lenses
A converging (convex) lens is thicker in the middle and bends parallel rays inwards to a focus. A diverging (concave) lens is thinner in the middle and spreads parallel rays outwards.
For ray diagrams of a converging lens, use these rules:
- A ray parallel to the principal axis refracts through the focal point F.
- A ray through the centre of the lens passes straight through undeviated.
- A ray through F refracts parallel to the principal axis.
The intersection of any two rays gives the image position. Image properties depend on object distance:
| Object distance | Image | Use |
|---|---|---|
| > 2F | Real, inverted, smaller | Camera |
| Between F and 2F | Real, inverted, larger | Projector |
| < F | Virtual, upright, larger | Magnifying glass |
Sound: loudness and pitch
A sound wave on an oscilloscope shows two key features:
- Amplitude = maximum displacement of the wave from rest. Larger amplitude → louder sound.
- Frequency = number of waves per second (Hz). Higher frequency → higher pitch.
Wave speed: v = f × λ (m/s). Sound in air ≈ 340 m/s; in water ≈ 1500 m/s; in steel ≈ 5000 m/s.
CCEA tip
Refraction questions almost always award B1 for drawing the normal correctly. Skip it and you cap your possible score before doing any physics.
AI-generated · claude-opus-4-7 · v3-ccea-combined-science-leaves