Air Flow within the Crookes Radiometer

Megan K. Krupa, Azusa Pacific University
Timothy A. Heumier, Azusa Pacific University

Abstract

The purpose of this experiment was to explain how the Crookes Radiometer works. Inside a glass bulb are vanes supported on a vertical spindle. When we shine the light on the vanes, the vanes spin. This apparatus was created in the late 19th century and still has not been fully explained. To be able to discover what is occurring inside the bulb would increase the knowledge of the scientific community. My methods included using an equation to model the motion and analyzing video data to find the constants in the equation. Our exploration began by attempting to find the friction and damping constants of the forces acting on the vanes, concentrating on the mechanically excited data, or spinning the vanes by shaking the bulb. These forces act at all times. The negative acceleration was much greater with thermal excitation than with mechanical. The thought was to compare the mechanical with the thermally excited data, which is when we shined light on the vanes, to extract just the thermal forces involved. When I graphed the mechanically excited motion to find the constants, I found that they were not constant from run to run. This led me to conclude that there is another force acting which I postulate is an air flow occurring inside of the bulb as the vanes move. In the same state of thinking, I explored the possibility of an air flow occurring on the mechanically excited motion. If there is indeed an air flow occurring, then this could explain why the negative acceleration of the thermally excited motion is so much greater than the negative acceleration of the mechanically excited motion. More work can be done to explore how an air flow would affect the vanes and more can be done computation wise, as my conclusions were mainly conceptual.

 
Nov 12th, 1:00 PM Nov 12th, 2:00 PM

Air Flow within the Crookes Radiometer

HUB 302-171

The purpose of this experiment was to explain how the Crookes Radiometer works. Inside a glass bulb are vanes supported on a vertical spindle. When we shine the light on the vanes, the vanes spin. This apparatus was created in the late 19th century and still has not been fully explained. To be able to discover what is occurring inside the bulb would increase the knowledge of the scientific community. My methods included using an equation to model the motion and analyzing video data to find the constants in the equation. Our exploration began by attempting to find the friction and damping constants of the forces acting on the vanes, concentrating on the mechanically excited data, or spinning the vanes by shaking the bulb. These forces act at all times. The negative acceleration was much greater with thermal excitation than with mechanical. The thought was to compare the mechanical with the thermally excited data, which is when we shined light on the vanes, to extract just the thermal forces involved. When I graphed the mechanically excited motion to find the constants, I found that they were not constant from run to run. This led me to conclude that there is another force acting which I postulate is an air flow occurring inside of the bulb as the vanes move. In the same state of thinking, I explored the possibility of an air flow occurring on the mechanically excited motion. If there is indeed an air flow occurring, then this could explain why the negative acceleration of the thermally excited motion is so much greater than the negative acceleration of the mechanically excited motion. More work can be done to explore how an air flow would affect the vanes and more can be done computation wise, as my conclusions were mainly conceptual.