The Atoms Family - Dracula's Library

Dracula has just finished building his radiometer rack to alert him when too much light is present. Since he's afraid of the light, he wants you to test it out for him.

Aim the light (your mouse) at the radiometers below and observe how they react.

Notice how the sails on the radiometers spin after the light is shining on them. A radiometer consists of a set of vanes, each shiny on one side and blackened on the other.

When the light strikes the shiny surface, most of it is reflected away, but when it strikes the blackened surface, most of it is absorbed, raising the temperature of the surface. The vanes turn because the air near the blackened surface becomes hotter and exerts a greater pressure on it than on the shiny surface.

Light has qualities of both waves and particles. These radiometers demonstrate the particle-like nature of light: when the photons of light strike the surface of the radiometer they transfer their energy and cause the sails to spin. Tell Dracula that everthing is working perfectly with his new light detection system!