Light and the electromagnetic spectrum

The room, the sunlight, the prism, the thermometers, the strip, the laser and the ladder are simulated. The light’s paths are drawn in one plane, as in a ray diagram, and the band of colours, about 9 cm on the card, is drawn two or three times wider than a real prism this close to the card would make it. The temperature rises are the model’s values, chosen to show the pattern Herschel found: every part of the spectrum heats a black bulb, and the bulb just beyond the red warms most. Real rises depend on the weather and the thermometers. The 5 minutes are sped up.

Ordinary glass absorbs much of the Sun’s ultraviolet, so the strip’s glow is drawn brighter than a real one. Infrared and ultraviolet cannot be seen: the orange dashed arrows only mark where they go. The ladder gives each region one rung, but real regions run into each other, and each device card shows one main use.

With reduced motion each step happens at once: the light, the thermometers, the strip and the laser appear straight away as they are at the end of the step, and the 5 minutes pass at once.