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Electromagnetic Waves

This article provides an overview of electromagnetic waves, including how they travel, their speed, and the evidence for their dual nature as both waves and particles. It also explores the different types of electromagnetic waves in the spectrum and how light behaves when it interacts with different materials. The article concludes with a discussion on the colors of objects and the primary colors of light and pigment.

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Electromagnetic Waves

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  1. Electromagnetic Waves Chap. 18

  2. What are Electromagnetic Waves? • Electromagnetic waves are produced when an electric charge vibrates or accelerates.

  3. How they Travel • They can travel through empty space as well as through matter! • The transfer of energy by electromagnetic waves traveling through matter or across space is called electromagnetic radiation.

  4. Speed of Electromagnetic Waves • Yes, electromagnetic waves travel at a constant speed through a vacuum, c. • The speed of light in a vacuum is 300,000,000 m/s.

  5. Michelson’s Experiment • See pg. 534 in your text.

  6. Measure the speed • The equation here is the same as the one for mechanical waves. • Speed = wavelength x frequency

  7. Wave or Particle? • What is light? • There are two theories.

  8. Evidence for a Wave

  9. Another view or this

  10. Light is a Particle • Electrons are emitted from a metal plate when blue or ultraviolet light strikes it.

  11. Dual Nature of Light

  12. Light Intensity • Intensity of light decreases as photons travel farther from the source. Because the total energy does not change, the wave’s intensity decreases.

  13. The Electromagnetic Spectrum

  14. Types of Electromagnetic Waves • Radio waves: Used in radio and television technologies, as well as in microwave ovens and radar. • Infrared: Used as a source of heat and to discover areas of heat differences. • Visible Light: The part of the spectrum that is visible to humans.

  15. Ultraviolet Rays: Have applications in health and medicine, and in agriculture. • X-Rays: Used in medicine, industry, and transportation to make pictures of the inside of solid objects. • Gamma Rays: Used in the medical field to kill cancer cells and make pictures of the brain, and in industrial situations as an inspection tool.

  16. Behavior of Light • How light behaves when it strikes an object depends on the material the object is made of. • Materials can be: • Transparent • Translucent • Opaque

  17. Transparent? Translucent? Opaque?

  18. Transparent? Translucent? Opaque?

  19. Transparent? Translucent? Opaque?

  20. Interactions of Light • When light strikes a new medium, it can be reflected, absorbed, or transmitted. • When it is transmitted, it can be refracted, polarized, or scattered.

  21. Reflection, Absorption, Transmission • Regular reflection: when parallel light waves strike a surface and reflect all in the same direction. • Ex:

  22. Diffuse Reflection • When parallel light waves strike a rough, uneven surface.

  23. Refraction • A light wave can refract, or bend, when it passes at an angle from one medium into another.

  24. Refraction Again

  25. Refraction, one last time Refraction Reflection and Refraction

  26. Refraction, one last time • index of refraction • Diamond 2.419 • Ethyl Alcohol 1.361 • Cubic Zirconia  2.21 • Ice 1.309 • Glass (flint)1.66 • Water  1.333 • Glass (crown) 1.52 • Air 1.000  Refraction Reflection and Refraction

  27. Polarized Polarizers

  28. Another view of polarizing filters

  29. Scattered • Earth’s atmosphere contains many molecules and other tiny particles. These particles can scatter sunlight. Scattering means that light is redirected as it passes through a medium.

  30. Scattering • The lower the sun is on the horizon, the more of the atmosphere the light travels through before it reaches Earth’s surface. By this time, most of the blue and green wavelengths of light are scattered, so all we see are reds and oranges.

  31. Color • As white light passes through a prism, shorter wavelengths refract more than longer wavelengths, and the colors separate. • This process is called dispersion.

  32. A rainbow is an example of dispersion. Droplets of water act like prisms. Light slows down and refracts when it enters a raindrop. It refracts again as it exits the raindrop, speeds up, and travels back toward the source of the light.

  33. refraction • diamond cubic zirconia refraction applet - Google Search • applet diamond refraction - Google Search • Molecular Expressions: Science, Optics and You - Refraction of Light: Interactive Java Tutorial

  34. Colors of Objects • The color of any object depends on what the object is made of and on the color of light that strikes the object.

  35. Primary Colors of Light

  36. Secondary Colors of Light

  37. Primary Colors of Pigment

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