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Color Absorption and Reflection: Light into Heat Energy

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Color Absorption and Reflection: Light into Heat Energy

Physical Science

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Learners investigate the changes in water temperature due to different colored lights and filters.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain that absorbed light energy is converted to heat energy.
  • Explain that as a greater amount of light energy is absorbed, a greater change in temperature is expected.
  • Explain that white light heats an object more than lights of other colors because it carries more energy.

Everything You'll Have Covered

Light is electromagnetic radiation, and visible light is a very small part of the electromagnetic spectrum. Visible light has various colors corresponding to different wavelengths. White light, such as sunlight, is made up of the whole spectrum of wavelengths of visible colors. A prism bends light to make different colors visible. The amount of bending usually depends on the wavelength of the light. Wavelengths of visible light include the array from longer red waves to shorter violet waves. The entire spectrum of visible colors is made up of seven main colors: red, orange, yellow, green, blue, indigo, and violet. It is important to note that the colors of a spectrum or rainbow are not distinct stripes. Instead, there is a gradual variation between colors.

Light may be reflected, absorbed, or refracted by objects. We typically think of shiny objects reflecting light, but all objects reflect light. In fact, for an object to be visible, it must reflect some light back to our eyes. The color of an object depends on the wavelengths of the light it reflects. When white light strikes the red petals of a rose, the petals absorb all wavelengths of light, except for red, which it reflects back to our eyes. The green stem and leaves of the rose absorb all wavelengths of light, except for green, which they reflect. Since black is not a color that is present in visible light, objects that appear black absorb all colors of light and reflect little or no color. Object that appear to be white reflect all colors of visible light.

Light is a wave that carries energy, and absorbed light energy is converted to heat energy. As a greater amount of light energy is absorbed, a greater change in temperature is expected. Different colors of light carry different amounts of energy, and the color of light affects temperature change. Since white light includes all other visible colors, it carries the total energy carried by those colors. White light causes the greatest temperature increase of all visible colors of light. Blue objects absorb a smaller amount of energy than green or red ones, and blue objects stay cooler. Red objects absorb most of the energy carried by white light, which results in a greater temperature increase than objects of other visible colors. Black is not a color present in visible light. Objects that appear black absorb all colors of light, and that results in a greater increase in temperature than light absorbed by an object of any visible color.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts color, light
Course Physical Science
Type of Tutorial Experiment
Key Vocabulary absorption, color, energy