School of Physics Lecture Demonstration Manual

He-1 Crookes Radiometer

Published: Monday 13 March 2006 - Updated: Monday 28 March 2011


To demonstrate a sensitive detector of thermal radiation.



Click on pictures to enlarge.

Crookes radiometer Diagram


The radiometer consists of four light mica vanes blackened on one side and silvered on the other and arranged on a common pivot so that they may rotate freely in a horizontal plane. The glass container is evacuated to a pressure of approximately 10 mm of mercury. At this pressure there are still many gas molecules to interact with the vanes and the mean free path is large.

Safety notes

Electrical safety

Sharps Safety


top of page