Good responses to the "color correcting lens" question prompted me to
consider an option of separating spectral lines in parallel plates.
Nothing profound, only a good discussion topic.
Suppose that n=1.500 for lambda1 and n=1.505 for lambda2 in a parallel
glass plate (flint) whose thickness is one meter. A narrow beam of light
(lambda1 and lambda2) is intercepted at an incident angle of 55 degrees.
Using the well known formula for the beam lateral displacement, d, one
finds d=44.52 cm for lambda1 and d=44.70 mm for lambda2. The two emerging
beams, each parallel to the initial light direction, will be separated by
the distance 1.8 mm.
It is not likely that a very thick plate can be found but an aquarium with
water may be invetigated. I am not suggesting that separation of colors by
parallel plates may have advantages over practically used techniques. Yes,
there are better topics for using limited class time, but that is another
subject. (I know teachers who spend 80% of time on mechanics.)
By the way, you may ask students to show that, theoretically, separation
of colors has a broad maximum, in this case near 55 degrees.
Ludwik