Untitled Document

Physics Demo Number: 007

Approximate

Run Time: 5 min

Radiometer , Propane Torch, and Cherry- Red Heated Expansion Ball for Blackbody Radiation

Demo Description

Use a radiometer and flashlight to show the usual incorrect direction of vane rotation , which precludes one from being able to explain the rotation as arising from radiation pressure from optical wavelengths .

Then heat an iron ball up to red hot and see the radiometer spin even faster (than the flashlight case) thanks to the invisible infrared radiation coming from the ball.

Scientific Principles

Heated gas molecules rebound more energetically from a hotter ( black ) surface than from a cooler ( shiny) surface.

Equipment

Radiometer
Flashlight
Propane Torch
Iron Ball on Thermally Insulating Handle
Document Camera

Equipment Location

Kit (007) on [A-1-5] contains the Radiometer, the Flashlight , and the Iron Ball on a rod.
The Torch is in Kit (125) on [D-3-5].
The Document Camera lives in the Lecture Hall.

Instructions

The radiometer, torch and iron ball are shown in the first photo.

The second photo shows the radiometer on the document camera.

The third photo shows the projected image of the radiometer on the lecture hall screen as seen from the back of the lecture hall.