When I hold 2 ordinary playing cards edge-to-edge, nearly touching
each other (actually touching slightly, but with a space I can look
through in between the touching points) up to one eye, very close, I
can see many parallel lines running parallel to the card edges.
(Perhaps only a nearsighted person can see this?)

--- Is this "single slit diffraction"?

--- Where can I find the math that describes this?

--- Is there agreement on what is causing this phenomenon?

daniwe... at (no spam) gmail.com wrote:

When I hold 2 ordinary playing cards edge-to-edge, nearly touching
each other (actually touching slightly, but with a space I can look
through in between the touching points) up to one eye, very close, I
can see many parallel lines running parallel to the card edges.
(Perhaps only a nearsighted person can see this?)

--- Is this "single slit diffraction"?

--- Where can I find the math that describes this?

--- Is there agreement on what is causing this phenomenon?

When the edges of the slit are not clean straight lines you can get
apodized throughput. Finite thickness also affects the pattern. Good
slits are formed of parallel unused razor blade edges cleaned of oil.

Google
"single slit diffraction" 15,600 hits

Shoot a laser pointer between the opposed cards onto a wall.

--
Uncle Alhttp://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)http://www.mazepath.com/uncleal/lajos.htm#a2

When I hold 2 ordinary playing cards edge-to-edge, nearly touching
each other (actually touching slightly, but with a space I can look
through in between the touching points) up to one eye, very close, I
can see many parallel lines running parallel to the card edges.
(Perhaps only a nearsighted person can see this?)

--- Is this "single slit diffraction"?

--- Where can I find the math that describes this?

--- Is there agreement on what is causing this phenomenon?

daniwe... at (no spam) gmail.com wrote:
When I hold 2 ordinary playing cards edge-to-edge, nearly touching
each other (actually touching slightly, but with a space I can look
through in between the touching points) up to one eye, very close, I
can see many parallel lines running parallel to the card edges.
(Perhaps only a nearsighted person can see this?)

--- Is this "single slit diffraction"?

--- Where can I find the math that describes this?

http://en.wikipedia.org/wiki/Diffractionis a good starting point,
particularly the subsection on "Single-slit Diffraction").http://en.wikipedia.org/wiki/Diffraction_formalismgives a bit
more of the mathematics.

--- Is there agreement on what is causing this phenomenon?

It's fundamentally a consequence of the wave-like nature of light.
This, in turn (like all the laws of classical optics), can be derived
from the Maxwell equations (see, for example, the textbook by Jackson,
"Classical Electrodynamics", now in its 3rd edition).

--
-- Jonathan Thornburg [remove -animal to reply] <J.Thornb... at (no spam) soton.ac-zebra.uk
School of Mathematics, U of Southampton, England
"When you find that your views match [those of] the majority, it's
time to pause and reflect." -- Samuel L. Clemens, a.k.a. Mark Twain