# Derin Sherman's educational videos

I've created a number of educational videos, which often appear on their own web pages. For convenience, they are all listed here.

### Plasma globe circuit

A very simple circuit that creates a plasma globe using a circuit very similar to the plasma speaker circuit shown below. The major difference between this circuit and the plasma speaker is that this circuit drives a UC 12T ignition coil instead of a flyback transformer. The ignition coil runs at a lower current, so there's no need for the 3 ohm power resistor used with the flyback. Also, the induction coil operates at a lower frequency (mine ran at about 6kHz) which means using different RC values for the 555 timer. Although it is possible for you to build this circuit, you should not try to do so unless you are familiar with high voltage electricity.

The schematic for this circuit is available in PDF format here: http://people.cornellcollege.edu/dsherman/plasma-ball-circuit.pdf

### Plasma speaker: making musical sparks

A proof-of-concept system showing that it is possible to generate acoustic music from sparks. This is a system that you could build yourself, atlhough you should not attempt to build this system unless you have experience working with high voltage electricity. This circuit is based on the circuit shown in the YouTube video http://www.youtube.com/watch?v=xv_MS9nBZyw with some small modifications.

The schematic for this circuit is available in PDF format here: http://people.cornellcollege.edu/dsherman/plasma-speaker-circuit.pdf Please note that the schematic also provides sources for some of the more obscure parts.

### Wireless power transmission

A demonstration of a wireless power transmission system build by Cornell College students Lucas Jorgensen and Adam Culberson. This system uses a pair of magnetically coupled resonators. Power is propagated via an evanescent wave. This is a system that you could build yourself.

More information explaining the theory behind this form of wireless power transmission is at http://www.mit.edu/~soljacic/wireless-power_AoP.pdf and a more detailed list of resources is available at http://www.mit.edu/~soljacic/wireless_power.html

### McCollough Effect illusion

This video demonstrates the McCollough effect illusion. This is related to afterimages insofar as it will induce a complementary color, but is different in that it is far more persistant than an afterimage.

### Making a radio using an oscilloscope

This video shows how to make an AM radio using an oscilloscope, an inductor, a capacitor, a solar cell, and an amplified speaker. When the inductor and capacitor are connected together, they form an electrical oscillator. If this oscillator is tuned to the same frequency as a nearby radio station, the oscillator will resonate with the radio station and develop a voltage proportional to the transmission signal. We can see this signal using an oscilloscope to measure the voltage across the capacitor. As the radio signal increases, the oscilloscope trace grows larger, and more light appears on the oscilloscope screen. We can use a solar cell to convert this flickering light signal back into an electrical signal. When the solar cell is connected to a speaker, the speaker will convert the electrical signal back into sound, and we can hear the radio.

### Solar cell impedance spectroscopy

The Cornell College physics department is working to develop new solar cells based on organic dyes and quantum dots. The behavior of these cells can be characterized by measuring the complex impedance of the solar cell as a function of frequency. This technique is known as impedance spectroscopy, and this video shows physics students Talon Holmes and Nathan Jepsen in the process of designing and creating a system to perform these measurements. The "cell" they are testing in this video is actually an electrical model of a solar cell consisting of a few resistors and capacitors. The figures shown on the computer monitor are actual measurements of the model circuit.

### Physics game

The "Physics Game" is a Blender program that can run on Windows, Mac, and Linux operating systems. The program lets students perform physics experiments in a virtual world. Students can modify the virtual world, and can even modify the laws of physics in the virtual world.

### Blender Motion Tracking Test - Snub Dodecahedron

The free Blender program can be used in conjunction with the free Voodoo motion tracking software to integrate visual elements of the virtual Blender world with video footage from the real world.

A useful tutorial showing how to integrate Blender objects into movies is here.

### Using strobe light to make water drops fall in slow motion.

This video shows how to use a strobe light to make water drops fall in slow motion. The drops of water are being forced out of the tube at 60 Hz. If the strobe light flashes at 60 Hz, then the drops appear suspended in space without any motion at all. If the strobe flashes at a slightly slower frequency, then the drops appear to fall downward in slow motion. If the strobe flashes at a slightly higher frequency, then the drops appear to fall upward in slow motion.

### Transmission hologram viewed in red and green laser light

A transmission hologram is actually a complex diffraction grating. It is well known that light passing through a diffraction grating will be deflected through an angle that is proportional to the wavelength of the light. This is why diffraction gratings can make rainbows when white light is passed through them. The white light consists of a range of colors and the diffraction grating deflects each color through a different angle. A transmission hologram will do the same thing, and this gives rise to a more subtle effect: the size of the reconstructed holographic images are proportional to the wavelength of laser light used to illuminate the hologram.

### Making Quantum Dots

The Cornell College physics department is working to develop new solar cells based on organic dyes and quantum dots. This video shows Valerie Collins in the process of creating a series of quantum dots each with a slightly different size. As the quantum dots grow larger, their adsorption spectra changes and the color of the dots changes accordingly. All the quantum dots shown here are chemically identical, but their spectra are all different.

### Evanescent waves

Snell's law dictates the angle through which light is refracted when it passes from one transparent medium to another. In some cases, Snell's law predicts that the angle of refraction is greater than 90 degrees. In these cases, the light ray is not transmitted but is completely reflected. However, light is actually a wave and some of the wave does enter the "forbidden" medium. This video shows a computer animation of this effect: waves with an angle of incidence greater than the critical angle travel through the blue medium towards the green medium. The waves reflect off the interface with the green medium, but there is an exponentially decaying wave (the evanescent wave) present in the green medium. The motion of the wave fronts can be seen by tracking the three brightly colored balls that ride along with the wavecrests: each ball reflects off the interface with an angle of reflection equal to the angle of incidence.

Evanescent waves are now being developed as a means of wirelessly powering portable electronic devices. Cornell College physics students Lucas Jorgensen and Adam Culberson have constructed a wireless power transmission system using evanescent waves and magnetic resonance.

### Exploring Virtual Worlds

Terragen is a program that lets you create photorealistic fractal landscapes. Terragen does not use any digitized images to create the landscape. Instead, it uses fractals to model the mountains and clouds. It also uses raytracing to determine the interaction of light with the objects in the scene. I have used Terragen in my PHY-125 class (Science through Film and Fiction) as a demonstration of the power of equations to model the real world.