Strange occurrence on office wall.


by Jilang
Tags: occurrence, office, strange, wall
Jilang
Jilang is offline
#1
Jan9-14, 12:57 PM
PF Gold
P: 366
Quite late this afternoon I noticed a series of perfectly formed circles of light on the wall above my computer. Where are they coming from I wondered? Putting my hand in front and tracing one back the window, then climbing onto a chair it was clear they originated from the little holes at the top of the vertical window blinds. What was weird though is that the holes are perfect squares, but the light patterns were perfect circles! I invited my colleagues in to witness this "strange phenomenon" and they went away scratching their heads. Wanted to share this as it was the most entertaining thing that happened today at work!
Phys.Org News Partner Physics news on Phys.org
Sensitive detection method may help impede illicit nuclear trafficking
CERN: World-record current in a superconductor
Beam on target: CEBAF accelerator achieves 12 GeV commissioning milestone
mfb
mfb is online now
#2
Jan9-14, 01:15 PM
Mentor
P: 10,767
The sun is a nearly perfect circle, and the small hole is nearly like a point (compare the spot size to the hole size to check this), so you have a cone of light coming in and a cone of light going out. Basically a pinhole camera image of the sun.

During solar eclipses, all those spots become crescents and you get fascinating images like this.
Jilang
Jilang is offline
#3
Jan9-14, 01:25 PM
PF Gold
P: 366
Spoiler! LOL.

jtbell
jtbell is offline
#4
Jan9-14, 01:26 PM
Mentor
jtbell's Avatar
P: 11,220

Strange occurrence on office wall.


If the sun were a point object, then the square apertures would indeed produce bright square spots on the wall, except for possible diffraction fringes.

The sun isn't a point object, so it behaves as a collection of point objects, distributed over a circular disk. Each of these sources produces a bright square spot on the wall. The centers of these square spots are distributed in a circular disk, so the square spots overlap to produce a larger circular disk.
Jilang
Jilang is offline
#5
Jan9-14, 01:37 PM
PF Gold
P: 366
Thanks folks. It did have me scratching my head for a minute too until I saw some clouds going past over the disc. Couldn't see any sunspots though!
sophiecentaur
sophiecentaur is offline
#6
Jan9-14, 05:15 PM
Sci Advisor
PF Gold
sophiecentaur's Avatar
P: 11,341
You just happened to make yourself a pinhole camera!

A few years ago, the Sun was in just the right position to shine through a small hole in the back bedroom window blind in my house and form an image on the front door. via the staircase, at just the right angle. The 'throw' from hole to door was long enough to produce an image of a couple of cm diameter. You could clearly see some sunspots on the image. My son and I were 'well impressed'.
Cephas Atheos
Cephas Atheos is offline
#7
Jan9-14, 07:47 PM
P: 4
I saw some wonderful curves from sunlight scattered from a half-full glass of light machine oil. Bernoulli curves, cycloids, and combinations kept a colleague and I entranced for nearly an hour!

We even tried adding water to see more - and different coloured - curves.

I was still gobsmacked by the tree shadow image from mfb's link. Wonderful.
davenn
davenn is offline
#8
Jan9-14, 10:58 PM
Sci Advisor
PF Gold
davenn's Avatar
P: 2,241
Quote Quote by Jilang View Post
Thanks folks. It did have me scratching my head for a minute too until I saw some clouds going past over the disc. Couldn't see any sunspots though!
that's a pity as there's a couple of big spots on there at the moment

Dave
Jilang
Jilang is offline
#9
Jan10-14, 02:17 AM
PF Gold
P: 366
Quote Quote by davenn View Post
that's a pity as there's a couple of big spots on there at the moment

Dave
I guess the resolution was not good enough, the holes are 4mm square. If I see it again I have a plan involving Blue Tack......
A.T.
A.T. is offline
#10
Jan10-14, 04:16 AM
P: 3,536
Quote Quote by Jilang View Post
What was weird though is that the holes are perfect squares, but the light patterns were perfect circles!
Measuring from the wall, the holes have smaller angular size than the sun. If you increase their size, or bring them closer to the wall, the spots will become squares.
sophiecentaur
sophiecentaur is offline
#11
Jan10-14, 10:27 AM
Sci Advisor
PF Gold
sophiecentaur's Avatar
P: 11,341
Quote Quote by Cephas Atheos View Post
I saw some wonderful curves from sunlight scattered from a half-full glass of light machine oil. Bernoulli curves, cycloids, and combinations kept a colleague and I entranced for nearly an hour!

We even tried adding water to see more - and different coloured - curves.

I was still gobsmacked by the tree shadow image from mfb's link. Wonderful.
I'll have some of what he's having.
CWatters
CWatters is offline
#12
Jan10-14, 12:14 PM
P: 2,861
I made a crude pin hole camera to observe the transit of venus a few years ago. It worked quite well. Why not try it yourself next time ;-)
Jilang
Jilang is offline
#13
Jan10-14, 12:33 PM
PF Gold
P: 366
Thanks CW, I'm guessing the sun needs to be out right? This is a rare occurrence at the weekend so it looks like it will need to be another office experiment!
mfb
mfb is online now
#14
Jan10-14, 03:00 PM
Mentor
P: 10,767
Quote Quote by CWatters View Post
I made a crude pin hole camera to observe the transit of venus a few years ago. It worked quite well. Why not try it yourself next time ;-)
Like... December 2117? ;)

Quote Quote by Jilang View Post
I'm guessing the sun needs to be out right?
The contrast is orders of magnitude better with a visible sun, right.
Jilang
Jilang is offline
#15
Jan11-14, 02:20 AM
PF Gold
P: 366
I'm worried I'm going to miss it! Just trying to calculate the odds of it being daytime, sunny and occurring in my lunch break.....would I stand a better chance in Hawaii?


Register to reply

Related Discussions
How do I record the occurrence of waves? General Physics 14
Peculiar Occurrence Needs Explanation Chemistry 1
Microsoft Office 2003 vs. Microsoft Office 2007/2010 Computers 8
Static Shocks Occurrence General Physics 1
Wierd occurrence with Pepsi General Physics 8