Radiometer, Crooke’s, Single

Cheap in quality, For demonstrating the conversion of radiant energy into mechanical energy. Comprising a partly evacuated glass bulb of about 70mm diameter with a fine pivot on which a rotor having a set of four mica vane arms is delicately balanced. Each mica vane has one side painted matt black with other side bright. On exposing to sunlight or sufficiently bright incandescent light source, the absorption of radiant energy by the blackened side of vanes sets up a temperature differential with respect to the bright sides, which causes net force to be exerted by the air molecules on the blackened side making the vanes rotate with their bright faces leading. Mounted on a Bakelite base.