Blog post: swansont: Handy, but Not Deep Thoughts

A few weeks ago Doug Natelson had a post about handy numbers to know … if you're doing some kind of physics involving liquid nitrogen or liquid helium, or anything else in which a condensed-matter/nanoscale physicists might be involved. (I assume this is in addition to knowing basic constants)

But I do atomic physics. A few favorite things that help me out if I'm away from a calculator or reference book, with some additions from my colleagues. I probably knew more of these, once upon a time.

— The speed of light can be written as 30 GHz-cm. Thus a 30 GHz signal has a wavelength of 1 cm. 1 Ghz means 30 cm.

— 1 nanosecond is 1 foot (light travel in a vacuum)

— a 1 eV photon is 1240 nm

— Room temperature is 1/40 eV (kT)

— Planck's constant is 0.4 amu-microns/second (useful for deBroglie wavelength calculations)

General reference:

– $latex sqrt{g} = pi $ (to about 0.3%) Handy for Pendulum problems — just cancel or combine the two values.

Read and comment on the full post