Color Physics @Hampshire, Day 10

After reviewing the concepts of wavelength, amplitude, and frequency in general, we discussed the special case of electromagnetic waves and the electromagnetic spectrum. The key ideas covered were the

  • Inverse relation between the wavelength and frequency of an electromagnetic wave.
  • Intensity of a wave and its relation to the amplitude of the wave.

In a lecture-heavy portion of the class, we went over how different properties of an EM wave in the visible spectrum correlate with the hue, saturation, and brightness of the perceived light.  I used very good slides developed by Geoff Boynton at the University of Washington.

Geoff Boynton's slide on the relation of the width of the spectral intensity-distribution of light and the perceived saturation.
Geoff Boynton’s slide on the relation of the width of the spectral intensity-distribution of light and the perceived saturation.

We introduced the spectral intensity-distribution graphs for light sources and the distinction between spectral colors and non-spectral colors, but also reviewed additive color mixing in the context of the intensity-distribution graphs. We touched on the relevance of additive mixing to the pointillist painting movement developed by Seurat.

Students then used hand-held spectrometers to determine the intensity-distribution for the red, green, and blue LED’s we used in additive mixing exercises earlier in the semester.  We also tried to determine the spectrum of the mixture various pairs of lights. This was tricky because of the light pollution in the room and the fact that the light from two LED’s was coming from different angles and scattering within the spectrometer.  


Students measured and recorded the intensity distributions of light from LEDs.Students measured and recorded the intensity distributions of light from LEDs.

Some of the students got to start playing with color filters and explore their absorption spectrum, but more formal introduction was left for the following class.

Color Physics @Hampshire, Day 9

Day 9 was a continuation of our exploration of waves. The class time was divided into two main activities:

  • Working in groups on conceptual exercises related to waves (drawing waves, ranking them based on various properties, etc.), led by me.
  • Carrying out a more systematic study of waves on a slinky, which included quantitative measurements of the speed of a wave pulse, led by my colleague Fred Wirth who has offered to lend a helping hand this semester and who designed and coordinated this portion of the class.
Conceptual Exercises on Waves
Conceptual Exercises on Waves

At the end, we discussed as a class the solutions to some of the conceptual exercises.

Color Physics @Hampshire, Day 8

On Day 8, we investigated transverse waves.

  • Students did some prep work at home by playing with a PhET interactive simulation  exploring qualitatively various properties of a wave on a string, and recording their observations.

    PhET Interactive Simulation on Waves
                                                       PhET Interactive Simulation on Waves
  • In class, we introduced a transverse sine wave and students worked in groups to come up with a comprehensive list of properties of a sine wave needed to describe it to grandma. This led us to the concepts of amplitudewavelengthperiodfrequency, and speed, as well as their respective appropriate units. We subsequently practiced finding the values of these properties for three animated waves I made using Grapher.
  • At the end of the class, as a taste of things to come, students briefly made waves with slinkies.
Students making waves with slinkies.
       Making waves with slinkies.

Color Physics @Hampshire, Day 7

On Day 7, we finally got to understand what electromagnetic waves are.

  • Students used a wonderful HTML-based simulation of a radiating charge to explore how motion of an electrically charged particle affects its electric field lines. They wrote their observations, the key ones which we discussed as a class.

    A positive point charge and its field lines.
    A screenshot of the PhET simulation of an oscillating electric charge and its electric field.
  • After briefly talking about the creation of magnetic field by a changing electric field and vice versa (mostly in a hand-wavy way), we moved on to the more familiar representation of the electromagnetic wave far away from wiggling charged particle. For this we used a very nice Java simulation developed by Juan M. Aguirregabiria, the screenshot of which is shown below. The shift inspired a good discussion of the pros and cons of the two visual representations of the electric field (arrows and field lines) and the relation between the depictions of electromagnetic radiation in the two simulations.

Simulation of a plane electromagnetic wave.A screenshot of a simulation of a plane electromagnetic wave.

  • After discussing different types of electromagnetic radiation (UV, visible light, WiFi, microwave) and its effects and uses, we began discussing what it takes to make a wave in general.

 

Color Physics @Hampshire, Day 6

On Day 6, we began to unpack the statement that light is an electromagnetic wave, leaving the particle nature of light for a later discussion.

A styrofoam sphere prickled with toothpicks.
A toy model of the electric field lines of a spherically symmetric electric charge made of styrofoam sphere and toothpicks.
  • We discussed electric charge and electric force.
  • We introduced the concept of electric field!
  • We learned about two ways of visually representing the strength and the direction of the electric field, one with arrows at various points, the other with field lines. To get a better sense of the spatial distribution of the field, students built with styrofoam balls and toothpicks 3D models of the electric field of a spherically symmetric charge.
  • We worked on conceptual problems testing students’ understanding of the above concepts.

Color Physics @Hampshire, Day 5

On Day 5, we were familiarizing ourselves with notation and problem-solving strategies.

  • We completed more examples of units conversions and scientific notation.
  • We practiced problem-solving with examples relating speed, distance, and time 

We ended the class by deflecting a stream of water with an electrically charged balloon as a segue to the discussion of light as an electromagnetic wave!

Color Physics @Hampshire, Day 4

Day 4 consisted of wrapping up the discussion of HSB, introducing the RGB model, and setting the groundwork for the upcoming discussion of physics.

  • Review of of Hue, Saturation, and Brightness 
    • HSB cylinder
  • Additive color mixing: We organized our observations of mixing of colored light from the previous class and introduced the RGB color model.
    • Primary colors in additive mixing
    • Complementary colors in the additive system
    • RBG color model
    • RGB cube
  • Measurement in physics:
    • What is science?
    • Units and unit conversions
    • Scientific notation and orders of magnitude. We watched Powers of Ten to get a better sense of what different powers of ten mean in terms of different scales, so that we can assess our answers to numerical problems.

 

A scene from Powers of Ten™
Powers of Ten™

Other Resources: A student pointed me to an interactive catalog of objects of a vast range of sizes, organized by powers of ten http://htwins.net/scale2/

Color Physics @Hampshire, Day 3

Topics

  • Saturation, hue, and brightness
  • Additive Color Mixing

We started Day 3 by playing with the HSB sliders on a computer software to determine which properties of perceived color are referred to as hue, saturation, and brightness.

Hue, Saturation, and Brightness sliders
Playing with Hue, Saturation, and Brightness sliders to find out how they affect the color

 

 

 

 

 

 

 

 

 

After using the hand-held spectrometers to investigate the spectrum of a computer screen, cellphone screens, and the video projector, students made predictions about how brightness, saturation, and hue may be affected by mixing different amounts of red, green, and blue light and tested their predictions using primary color light sticks.

Making a prediction about color mixing and testing them.
Mixing light with primary colors and investigating how digital images recored by a cellphone differ from what is seen by the naked eye.

Physics of Color @Hampshire, Day 2

Topics: Physical and neurological mechanisms for perception of color

  • We began the class by discussing students’ responses to a short assignment asking them to paint something and investigate how its appearance changes when it is illuminated by different types of light. Examples of interesting and insightful experimentations pictured were done by Madeleine Perreault and Lindsey Appleyard. (The effects of taking a cellphone photograph to be discussed later!)
    The difference in appearance of a watercolor composition illuminated by a desk lamp and by sunlight, by Madeleine Perreault

 

A painting illuminated by full spectrum light and pink light, by Lindsey Appleyard.

 

 

  • We discussed the physical processes necessary for the perception of color to take place, including everything from the generation of light by a source to the neural processing of the light signals by the brain, and identified those which can be explained by fundamental physics.
  • Students investigated and made qualitative observations of the color spectrum of various sources of light using hand-held spectrometers.

Resources:

  • B. Conway, “Color consilience: color through the lens of art practice, history, philosophy, and neuroscience.” Annals of the New York Academy of Sciences, vol. 1251, The Year in Cognitive Neuroscience, 2012, pp. 77–94.

Physics of Color @Hampshire, Day 1:

Topic: Subjective experience of color, interaction of color, and afterimages.

Students experimenting with sheets of paper of various colors.
Experimenting with interaction of color.

Today we looked at Josef Alber’s color plates, experimented with afterimages, talked about the dress, and created our own interaction of color compositions.

PDF’s of select slides are available here.

Other Resources: