How does a 'open surface' of a closed loop look like?

[serverxeon]

im on the topic of electricity and magnetism, and came across walter lewin's lecture.

i cannot visualise how the 'open surface' of this solenoid will look like

is the open surface a riemann surface? or something else?

[PLAIN]http://wiki-images.enotes.com/thumb/b/b5/Riemann_sqrt.jpg/180px-Riemann_sqrt.jpg

thanks

 

[RedX]

I believe the correct terminology is helicoid.

A Riemann surface is something else entirely. I'm not a mathematician, but as I understand it, a Riemann surface is just a way to visualize different branches of a function and how they are related to each other.