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Electromagnetic Waves

Electromagnetic Waves. Electromagnetic Waves- transverse waves consisting of changing electric fields and changing magnetic fields Electric Field- a region of space exerts electric forces on charged particles Magnetic Field- a region of space produces magnetic forces.

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Electromagnetic Waves

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  1. Electromagnetic Waves

  2. Electromagnetic Waves- transverse waves consisting of changing electric fields and changing magnetic fields • Electric Field- a region of space exerts electric forces on charged particles • Magnetic Field- a region of space produces magnetic forces

  3. If one changes the other changes so they regenerate each other • Electromagnetic waves are produced when an electric charge vibrates or accelerates

  4. Electromagnetic waves can travel though a vacuum, or empty space, as well as through matter!

  5. Electromagnetic radiation- transfer of energy by electromagnetic waves traveling through matter or across space

  6. Thunder and Lightning

  7. Speed of Light • Albert Michelson (1852-1931)- American physicist who first measured the accurate speed of light.

  8. All electromagnetic waves travel at 3.00x108 m/s

  9. The only difference in electromagnetic waves is their wavelength and frequency • Remember: v=λf

  10. Wave or Particle? • Electromagnetic radiation behaves sometimes like a wave and sometimes like a stream of particles.

  11. Evidence for the Wave Model • Thomas Young (1773-1829)- English physicist

  12. Evidence for the Particle Model • Albert Einstein (1879-1955) • Proposed that light, and all electromagnetic radiation, consists of packets of energy called photons • Photoelectric effect- emission of electrons from a metal caused by light striking the metal

  13. Intensity • Intensity- the rate at which a wave’s energy flows through a given unit of area • The intensity of light decreases as photons travel farther from the source.

  14. Wavelength Range • Frequency Range • Common Uses • Interesting Information

  15. Behavior of Light • Light and Materials • Materials can be transparent, translucent, or opaque

  16. Transparent • A material through which you can see clearly; transmits light, which means it allows most of the light that strikes it to pass through

  17. Translucent • A material that scatters light; makes objects look fuzzy or unclear

  18. Opaque • Either absorbs or reflects all of the light that strikes it; you cannot see through these objects

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

  20. Reflection • Image- a copy of an object formed by reflected (or refracted) waves of light • Regular reflection- occurs when parallel light waves strike a surface and reflect all in the same direction (smooth polished surface) • Diffuse reflection- when parallel light waves strike a rough, uneven surface, and reflect in many different directions

  21. Refraction • Bending of waves as it passes through a new medium • Mirage- a false or distorted image caused by hotter air above the surface refracting light waves; often looks like water

  22. Polarization • Polarized light- light with waves that vibrate in only one plane • Polarized sunglasses have vertical polarized filters so that horizontal polarized light is blocked reducing glare

  23. Scattering- light is redirected as it passes through a medium

  24. COLOR

  25. Separating White Light Into Colors • White sunlight is made up of all the colors of the visible spectrum • As white light passes through a prism, shorter wavelengths refract more than longer wavelengths and the colors separate • Dispersion- process in which white light separates into colors • Red- longest wavelength- least bent • Violet- shortest wavelength- bent most

  26. Double Rainbow

  27. The 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. • Pigment- material that absorbs some color of light and reflects others • Photography Link

  28. Primary Colors- 3 specific colors that can be combined in varying amounts to create all possible colors • In Light: Red, Green, and Blue • In Pigment: Cyan, Magenta, and Yellow • Secondary Colors- Combination of 2 primary colors • In Light: Cyan, Magenta, and Yellow • In Pigment: Red, Green, and Blue

  29. Complimentary Colors • In Light: Any two colors that combine to make white • In Pigment: Any two colors that combine to make black

  30. The Law of Reflection • Ray diagram- shows how rays changed direction when they strike mirrors and pass through lenses.

  31. Virtual image- a copy of an object formed at a location from which light rays appear to come • Remember: rays do not actually come from behind the mirror!

  32. Concave Mirrors • Concave Mirrors- when the inside surface of a curved mirror is the reflecting surface • Focal point- the point at which the light rays meet • Real image- a copy of an object formed at the point where light rays actually meet • Can be viewed on a surface such as a screen • Concave mirrors can form either real or virtual images • When the object is farther from the mirror than the focal point, the reflected rays meet in front of the mirror • When the object is closer to the mirror than the focal point the reflected rays spread out and appear to come from behind the mirror

  33. Convex Mirrors • Convex mirrors- when the outside surface of a curved mirror is the reflecting surface • Convex mirrors always cause light rays to spread out and can only form virtual images

  34. Lenses • Light travels at 3.00 x 108 m/s in a vacuum. • As it passes through new media it slows down • Air- almost 3.00 x 108 • Water- 2.25 x 108 • Glass- 2.00 x 108

  35. When light enters a new medium at an angle, the change in speed causes the light to bend or refract

  36. Index of Refraction- the ratio of the speed of light in a vacuum to the speed of light in the new material

  37. Which material is the most lustrous? The least lustrous? • What percentage of light striking a sapphire gemstone enters it? • If a light ray strikes each material at an angle, in which material would the light ray bend the most? • The speed of light through and unknown gemstone is 1.69 x 108 m/s. Identify the gemstone.

  38. Lens- Object made of transparent material that has one or two curved surfaces that can refract light • Concave lens- curved inward at the center and is thickest at the outside edges • Concave lenses always cause light rays to spread out and can only form smaller virtual images • Convex lens- curved outward at the center and is thinnest at the outer edge • Convex lenses form either real or virtual images

  39. Convex lens • Concave lens

  40. Total Internal Reflection • Critical angle- angle of incidence that produces an angle of refraction of 90 degrees • Total internal reflection- the complete reflection of a light ray back into its original medium • Materials that have small critical angles are likely to cause most of the light entering them to be totally internally reflected

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