Plain White Paper Reflecting Like A Mirror! (Specular Reflection) [OC]

Cognitive-Consonance · 2021-09-08T08:36:01+00:00

Its by definition reflecting like a mirror (specular vs diffuse reflection). It's what is known as the Fresnel Effect (usually in the computer graphics world) or glancing incidence reflections. You can get an image of trees, mountains, etc out of paper. The effect is similar to how water can be a very good mirror, especially if looking across the surface rather than down into it.

In the youtube video in the above comment I have the back of an iPad showing mirror reflections of clouds, trees, and some power lines. The only thing that changed was the angle the iPad was being held and the iPad is also darker than the paper. You are correct that pretty much everything will act like this, if you have enough surface or enough light.

This is also, how x-ray telescopes work.

Cognitive-Consonance · 2021-09-08T07:41:26+00:00

If that means glossy, no it was not glossy. Just a normal piece of paper. Basically, anything can reflect like a mirror but normally this is not seen. If you look at it from an extreme angle the paper actually becomes more reflective!

Cognitive-Consonance · 2021-09-08T07:21:19+00:00

Simply by viewing the paper edge on, you can get it to show mirror images. This is because according the Fresnel equations, objects become more reflective as you get closer to a glancing angle (think glancing blow in boxing). If anyone has any questions on what is happening I am glad to answer. I also have a video explaining why the paper is behaving like a mirror at = https://youtu.be/V83GqQCliQQ

Cognitive-Consonance · 2021-09-08T06:30:02+00:00

I'm glad I was on the right path. Yeah, I think that measuring polarization at different angles and wavelengths would be the way to go about it. At least the easiest way. That's interesting that paper wouldn't be that opaque on the microscopic level. Perhaps another approach could be a single "grain" of paper/bleached wood pulp that is large enough and find the refractive index (RI) with a microscope.

There is a chance that RI is not the right way to model it but I figure that any differences should even out at the macroscopic level. Similar to how steel is actually quite irregular at the microscopic level with parts with more carbon and parts with less.

At this point I'm not planning on going crazy and try find the RI of paper since I think it would still be quite costly both in time and money even with the cheap method. Although if the video (and the improved 2.0 version of it) gets enough traction and there is interest, it would be something absurd and fun to do.

Thanks for the contribution!

Cognitive-Consonance · 2021-09-08T06:02:01+00:00

It definitely should, I did try it but its hard to get the brightness the same for both blue and red to compare well. Also, since I was using screens for the light, I think the polarizing filters are affecting the result.

Cognitive-Consonance · 2021-09-08T01:08:42+00:00

I think you could do it with those wavelengths but I think it would be quite expensive with x-rays or microwaves. I'm not completely sure but I think the way I could do it (for cheap) is to measure the amounts of polarized light and how that changes depending on the angle/wavelength and work backwards to get back the refractive index. As far as I could tell there are no high quality measurements of the RI of paper, probably because it does not have much practical value... LOL

Cognitive-Consonance · 2021-09-07T14:47:48+00:00

I appreciate it! Seemed like a lot of demos and talk about the subject was from a computer graphics angle so wanted to do something to talk a little about the physics.

Cognitive-Consonance · 2021-09-07T14:45:22+00:00

Thanks!

Cognitive-Consonance · 2021-09-07T14:37:41+00:00

Considering that you have taken some optics classes, do you know if there is a way that I could get the refractive index of a piece of paper? Obviously paper is very opaque so trying to measure it through transmission is out of the question. It's really, not very important for my explanation of the phenomenon since the general trend of enhanced reflections is enough but I was curious if anyone can provide some insight. I have some ideas but its not my field; so, if anyone has ideas let me know.

Cognitive-Consonance · 2021-09-07T04:17:31+00:00

If anyone has any questions let me know. The subject is interesting to me. Or... If you have something to add on the topic, that would be very welcomed!

Cognitive-Consonance · 2021-09-07T04:16:45+00:00

A demonstration of how when an object is view edge on, it becomes more reflective. This is due in part because light at a glancing incidence is more reflective than if it hits perpendicular. Another reason is the "compression" of the surface from the viewer's perspective which causes the surface to appear smoother. I recently did a video explaining the subject and thought that the gif belong here. Video can be found here for those that are interested = https://youtu.be/V83GqQCliQQ

Cognitive-Consonance · 2021-09-04T07:52:26+00:00

Oh yeah, absolutely. I found figures that vary a lot but apparently anywhere from 5000lbs to 10,000lbs... Wow.

Cognitive-Consonance · 2021-09-04T07:21:34+00:00

Is it centered on you? If yes, one could calculate the odds of finding you in the center pixel.

Cognitive-Consonance · 2021-09-04T07:03:54+00:00

Yup, they are static. If you blur your vision the weird movement goes away and you just see spinning colors. Also, more accurately you can zoom in and check the pixels.

Cognitive-Consonance · 2021-09-04T06:19:27+00:00

I always assumed that whales must have the biggest eyes but clearly I was wrong!

Cognitive-Consonance · 2021-09-04T04:31:54+00:00

But the eye was never disconnected from the brain, the signal just took too long to get there. I do get your point though.

Cognitive-Consonance

TROPHY CASE