General properties of waves
A wave transfers energy from place to place without transferring matter. In a transverse wave the vibrations are at right angles to the direction of travel; in a longitudinal wave they're along it. Every wave obeys . Waves reflect off barriers, refract when their speed changes, and diffract (spread out) through gaps.
≈ 30 minReflection and refraction of light
Light reflects so that the angle of incidence equals the angle of reflection, both measured from the normal. When light enters a denser medium it slows down and bends towards the normal: . Going the other way, beyond the critical angle all the light reflects back: total internal reflection, used in optical fibres.
≈ 35 minLenses and dispersion
A converging lens brings parallel rays together at its principal focus; a diverging lens spreads them out. With ray diagrams you can find where an image forms and describe it: real or virtual, upright or inverted, enlarged or diminished. A prism splits white light into a spectrum because each colour refracts by a different amount.
≈ 35 minElectromagnetic spectrum
Electromagnetic waves are transverse waves that all travel at m/s in a vacuum. In order of increasing frequency (decreasing wavelength): radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. Each region has its own uses; the highest frequencies carry the most energy and are the most dangerous.
≈ 25 minSound
Sound is a longitudinal wave made by vibrating objects: a series of compressions and rarefactions that needs a medium to travel through. Louder sounds have larger amplitude; higher-pitched sounds have higher frequency. Echoes are reflected sound; using distance speed time, and remembering the sound goes there and back, we can measure distances, including with ultrasound.
≈ 25 min