Over the last few years, the helical mirror or “spinner” has become a popular decoration for gardens and elsewhere. Even casual observation reveals intriguing optical properties, so the spinner is a good teaching tool. To facilitate student exploration, we suggest some questions and provide brief explanations.
REFERENCES
1.
The concave and convex axes are not exactly perpendicular due to a gradual change in the number of twists per length.
2.
Alan J.
DeWeerd
and S. Eric
Hill
, “Reflections on handedness
,” Phys. Teach.
42
, 275
–279
(May 2004
).3.
The image points for the two cross sections are bounded by the convex cross section's focal point and the concave cross section's center of curvature.
4.
Alan J.
DeWeerd
and S. Eric
Hill
, “The dizzying depths of the cylindrical mirror
,” Phys. Teach.
43
, 90
–92
(Feb. 2005
).5.
Héctor
Rabal
, Nelly
Cap
, and Marcelo
Trivi
, “Longitudinal magnification drawing mistake
,” Phys. Teach.
42
, 31
–33
(Jan. 2004
).6.
That is one that twists in the opposite way as a common right-handed screw.
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© 2006 American Association of Physics Teachers.
2006
American Association of Physics Teachers
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