A colleague from another department stopped by my office this morning with a question about parabolas and parabolic mirrors. In the simplest terms, his question was the following:
When parallel rays reflect off a parabola, do they always converge to a focal point?
As we can see in the diagram below, rays that are parallel to the axis of symmetry of the parabola reflect and converge on a focal point. What about parallel rays with a different slope?
The answer is “no,” and to convince him of this fact I turned to my new favorite application: GeoGebra. In a matter of minutes I whipped up an applet illustrating this fact and posted the applet online. I thought you all might like to see it too.
(By the way, does anyone know if it is possible to embed applets in WordPress.com blogs?)
[...] and focal points II Yesterday I wrote about parabolic mirrors. I pointed out that parallel rays hitting a parabola typically do not reflect back to a focal [...]
By: Parabolas and focal points II « Division by Zero on June 5, 2009
at 11:14 am
Yes, the GeoGebra applet can be embedded in WordPress. I suggest you look at the blog colleague Jon Ingram http://joningram.org. All the best.
By: Sime S. on June 6, 2009
at 4:00 pm
Sorry, it’s WordPress, not WordPress.com. Sime S.
By: munshi2 on June 7, 2009
at 4:29 am
Thanks, that’s what I was afraid of.
By: Dave Richeson on June 7, 2009
at 7:10 am