Re: 632.8 nm

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Wed, 11 Apr 2001 17:32:55 -0400 THOMAS SANDIN <sandint@NCAT.EDU>
writes:
>         "Everyone knows" that the red light from a He-Ne laser is at
> 632.8  nm--or is 632.8 nm the vacuum wavelength lambda naught?
>         If so, when we give diffraction and interference problems
> that occur in air, shouldn't we use lambda = 632.8 nm/1.00029 = 632.6
> nm?
>                                                 Tom Sandin


In an introductory physics class it is rarely important  to require
answers to problems that are correct to four significant figures.

Even in the physics lab, students are rarely required to make
measurements
with an error of 0.03 percent or less.   How many high school or college
physics labs require students to measure the index of refraction of air
(which is 1.00029 only when corrections are made for the temperature,
pressure,
and other variations of pure air in the laboratory)

However, there is some advantage for asking students to solve diffraction

and interference problems that include the index of refraction of air,
carbon
dioxide, argon or other media as well as transmission through vacuum.  It
can provide another challenging task for the brighter students ....
especially
when problems require answers that must be correct to six significant
figures

Herb