e/m


eOverM

This image is a photograph of an electron beam passing through low pressure mercury gas. The electrons in the electron beam excite electrons in the Mercury atoms to higher energy levels (actually the beam is also likely ionizing most of the atoms), and then, as the mercury electrons cascade back to the ground state, they emit characteristic wavelengths of light, one of the brightest being the blue light at 435.835 nm that you see here. Those of you that have completed two semesters of physics should know why the beam is moving in a circle. The orange-red cylinder at the bottom left encloses a hot filiment from which the electrons are emitted. 

All technicality aside, I really posted this image because I like what I see as its minimalist geometric design. And knowing that I am looking at visual evidence of the passage of subatomic particles traversing a uniform magnetic field created by helmholtz coils only adds to my appreciation of the image, it doesn't subtract from it.