# Dispersion of Light/Electromagnetic Spectrum

## Dispersion

Definition, including the dispersion of light in a prism. Demonstration that the combination of all colors of light is white using a rotating disk.

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## How We See Colors

Table of wavelengths for visible light. The primary colors of light, including a color triangle. Demonstration of creating yellow and orange light from combinations of red and green light.

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## Demonstration: Benham Top

A black and white top which gives the illusion of color when rotated.

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• Watch {}video clip from Lecture 29 (40:20 - 43:37)

## Land's Famous Demonstration

Creating what appears to be a color image by superimposing two black and white images, one of which was taken with and is projected with a red filter.

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• Watch {}video clip from Lecture 29 (43:37 - 49:56)

## Polarization of Light

Definition, including Edwin Land's invention of the light polarizer and Malus' Law.

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• Watch {}video clip from Lecture 30 (0:00 - 8:50)

## Demonstration: Cross Polarizers

Looking through two polarizers, one of which is rotating to alternately block out the polarized light and allow it to pass through.

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• Watch {}video clip from Lecture 30 (8:50 - 10:19)

## Polarization by Reflection Off a Dielectric

Explanation of this method, and justification using Maxwell's Equations and the properties of reflection and refraction. The Brewster Angle for full polarization.

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• Watch {}video clip from Lecture 30 (10:19 - 20:35)

## Demonstration: Brewster Angle

Polarizing light by shining it at an angle off of a piece of glass.

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• Watch {}video clip from Lecture 30 (20:35 - 23:40)

## Polarization and Conductors

Conductors do not reflect linearly polarized light.

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• Watch {}video clip from Lecture 30 (23:40 - 24:42)

## Polarization by Scattering

Creating polarized light by scattering over 90° with small particles. Explanation that for very small particles, blue light scatters more frequently than red light.

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• Watch {}video clip from Lecture 30 (24:42 - 35:39)

## Demonstration: Scattering

Scattering light using cigarette smoke with small and large particles.

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• Watch {}video clip from Lecture 30 (35:39 - 40:54)

## Why the Sky is Blue

Explanation of how scattering makes the sky appear blue and the rising or setting sun appear red. Includes slides of stars that appear blue and a blue dust cloud around an astronaut on the moon.

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## Demonstration: Creating a Blue Sky

Creating a blue sky and a red sun in the classroom by shining light through a bucket of thiosulfate.

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• Watch {}video clip from Lecture 30 (46:03 - 51:27)

## Rainbows

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Fifteen questions about rainbows are posed. Explanation of how sunlight is reflected and refracted through a raindrop using Snell's Law.

• Watch {}video clip from Lecture 31 (0:00 - 7:36)

Further explanation of how rainbows are formed, including an explanation of the cone of light reflected back from a raindrop.

How we see a rainbow, including the appropriate angle to look into the sky.

## Secondary Rainbows

Discussion of the secondary rainbow, including the radius and color arrangement.

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Answers to twelve of the questions posed about rainbows at the beginning of the lecture.

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• Watch {}video clip from Lecture 31 (22:54 - 25:25)

## Slides of Rainbows

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A collection of slides of rainbows showing how they form, the primary and secondary rainbows, supernumerary bows, and white bows.

• Watch {}video clip from Lecture 31 (25:25 - 33:02)

More slides showing rainbow-like phenomena, including the 22 and 46° halo, sundogs, circles of light around the shadow of a plane on a cloud, and fog bows.

• Watch {}video clip from Lecture 31 (33:02 - 40:00)

## Polarization of Rainbows

Explaining why the light in a rainbow is highly polarized using the Brewster angle.

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• Watch {}video clip from Lecture 31 (40:00 - 45:21)

## Demonstration: Rainbow

Creating a rainbow by projecting light through a single drop of water and onto a large screen. Using a polarizer to show the polarization of the light in the rainbow.

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• Watch {}video clip from Lecture 31 (45:21 - 50:37)

## Color-Wavelength Chart

Chart showing the wavelengths for different colors of visible light.

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## True-False Questions

Four true-false questions: λ in different media, Poynting vector, polarization, total internal reflection.

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