The University of Texas at Austin, Department of Physics, College of Natural Sciences

4D20.10 • Mean Free Path: Crookes’s Radiometer

Photo of the Demonstration at the University of Texas at Austin.

Location: Cabinet 10 in 2.48

Instructions / Notes:

  • A Crooke's radiometer is placed in front of an electric lamp - The lamp is as a source of radiant heat energy.
  • The interior of the Crooke's radiometer is under partial vacuum.
  • One side of each pane is painted white, while the other side is black.
  • Thus, there is a small heat differential between the two surfaces.
  • A second radiometer, with a mirrored side, is used to show what happens when less radiant energy strike the panes.

Last updated on August 25, 2026