# A lot of fluid dynamics at Technopolis

Here Simon explains one more effect he has played with at home, the Magnus effect.

# Simon’s Community Contribution: Variation of 2D Casting Coding Challenge in p5.js

This is Simon’s version of Daniel Shiffman’s 2D Casting code, made on Wednesday last week right after the live session. Link to the live session including the coding challenge.

Code and interactive animation are online at: https://editor.p5js.org/simontiger/sketches/ugHX4yKQC
Play with the animation online at:
https://editor.p5js.org/simontiger/present/ugHX4yKQC
https://editor.p5js.org/simontiger/full/ugHX4yKQC

Simon has also made one more, optimized version of this project (with fewer rays, runs faster): https://editor.p5js.org/simontiger/present/F6TCHAZs_
https://editor.p5js.org/simontiger/sketches/F6TCHAZs_

Both of Simon’s versions have been added to the community contributions on the Coding Train website: https://thecodingtrain.com/CodingChallenges/145-2d-ray-casting.html

# Physics Experiments: Using an LED backwards

We have tried using an LED backwards: not get it to shine by letting an electric current pass through it but produce electricity by shining light on an LED (this is how solar panels work). It’s important to use a sensitive LED for this experiment, and as we have observed, it also seems to be important to use light photons of the same frequency as the colour of the LED (red laser didn’t work on a white LED, but it may have to do with the fact that red light is weaker than white light anyway, i.e. has a lower frequency). The picture below shows us measuring the voltage of the current produced by the LED.

We’ve have learned this and a a lot more from Steve Mould’s video on How diodes, LEDs and solar panels work: Photovoltaic cells and LEDs are both made of diodes. Diodes are designed to allow electricity to flow in one direction only but the way we make them (out of semiconductors) means that can absorb and emit light.

In the video, Steve shows how the semiconductor atoms share elctrons. Semiconductors are crystal structures of atoms are replaced by the atoms of neighboring elements, for example a structure where some silicon (Si) atoms are replaced by phosphorus (P) or boron (B) atoms, thus providing for free electrons inside the structure (N-type conductor) or for free “holes” unoccupied by electrons (P-type conductor). A diode is basically two semiconductors pushed together. With enough voltage, the electrones are able to jump from the N-type semiconductor across the depletion zone and into the P-type semiconductor, emitting light (photons) as they fill the holes and go from a high energy state into the low energy state.

If you shine a light at a diode, you can kick some electrons from their shells and thus create free electrons and holes that will move (because of the electric field in the depletion zone) and generate voltage.

# Physics Experiments: Double Slit

We have wanted to do the Double-Slit experiment for a long time. Finally, last Friday, armed with a suitable box, we ventured outside. To our common disappointment, light just wouldn’t behave as a wave this time, even though we had no detectors to check which slit the photons actually passed through. What we observed inside the box looked like two perfect stripes. No interference.

Experiment failure aside, we were in for a pleasant surprise, too: the box suddenly turned into a huge camera obscura! This is a picture of me and the blue sky as seen from inside the box!

When we got home, and tried to look inside the box again in the dimmer light in the living room, we were finally rewarded with this beautiful interference pattern:

We can only guess why it didn’t work outside. The wrong angle of the light beams (the sun being high in the sky above our heads)? Or maybe the light wat too bright, too many photons got in? The slits being too wide? We’ll be repeating this experiment for sure.

# What Does it Feel Like to Be Light? And Why the Infinity Tunnel is Actually Finite.

We were reading Steven Hawking’s A Brief History of Time, and Simon asked: “If the speed of light is the same relative to any body, is it the same relative to other light? How fast is light relative to itself? Is it stationary or does it have the speed of light?” We tried to imagine what it feels like to be a ray of light. Simon thinks that to light (or to a photon), time doesn’t exist. Does that mean that to light (to a photon), there is no causality? (Like a photon doesn’t know what happened first and what happened later – whether it first left the star Betelgeuse (640 light years away from the Earth) and then reached the Earth or the other way around?

Another observation from two days ago: Simon says that the tunnel appearing in the mirror once two mirrors are placed opposite to each other grows linearly with respect to time but always remains finite. Within one second, if you stand 1m away from the mirror, you will get 299 792 458 mirrors in your tunnel (because that’s how many times light will travel back and force during one second) or 149 896229 (half the previous number) small mirrors reflected in the large mirror:

# Experimenting with a Camera Obscura

Simon tests how well different light waves travel through the minuscule hole of the camera obscura.

# Electromagnetic Spectrum and the Opponent-process Theory

Simon has been fascinated about the Opponent-process theory (suggesting that color perception is controlled by the activity of three opponent systems, three independent receptor types which all have opposing pairs: white and black, blue and yellow, and red and green). He has been complaining that all the papers on Opponent-process Theory he has managed to find online were too superficial.

# Photons Trapped in Flemish Woods

Simon isn’t fond of magic or fantasy. Plus, he is not fond of long walks in the woods. Both “not fond of” are understatements. What was I counting on when I dragged him to the 2 kilometer long light installation in a forest close to Antwerp? I expected that seeing multiple fountains with photons trapped in water would make up for all the magic, scary music and the long walk. And it did!