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Light

Light. Remember…. Light is a form of Electromagnetic Energy Light travels as a Transverse Wave Light waves have wave characteristics Light travels faster in a less dense medium Light can travel through the vacuum of space, at the speed of 3 x 10 8 m/s (unlike sound).

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Light

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  1. Light

  2. Remember… • Light is a form of Electromagnetic Energy • Light travels as a Transverse Wave • Light waves have wave characteristics • Light travels faster in a less dense medium • Light can travel through the vacuum of space, at the speed of 3 x 10 8 m/s (unlike sound)

  3. Electromagnetic waves are created by mutually inducingelectric and magnetic fields at right angles to each other.

  4. applet Polarized Light-light which vibrates on a single plane

  5. When sunlight hits water, it polarizes the light horizontally.

  6. 'Rectilinear propagation' is a wave property which states that waves propagate (move or spread out) in straight lines. Pinhole camera Laser link A laser is a device that emits light through a process of optical amplification. (reflected coherent monochromatic waves)

  7. The frequency of vibration or oscillation of the charged particles determines the type of electromagnetic wave. Electromagneticwaves travel as a transverse waves.

  8. Classification Range of Frequencies Common Applications Radio Waves <1.0 x 109 Hz AM and FM radio, TV Microwaves 1.0 x 109 Hz – 3.0 x 1011 Hz Radar, aircraft navigation Infrared 3.0 x 1011 Hz – 4.3 x 1014 Hz Infrared photography, physical therapy Visible Light 4.3 x 1014 Hz (red) – 7.5 x 1014 Hz (violet) Photography, astronomy, microscopy Ultraviolet 7.5 x 1014 Hz – 5.0 x 1015 Hz Sterilization X Rays 5.0 x 1015 Hz – 3.0 x 1021 Hz Medical examination of bones, teeth, etc. cancer treatment Gamma Rays 3.0 x 1018 Hz – 3.0 x 1022 Hz Cancer treatment, food irradiation

  9. IR X-Ray

  10. Communication Frequencies:mostly lower than visible light

  11. INFRARED

  12. Is Cell Phone radiation harmful?

  13. ULTAVIOLET

  14. X-Ray waves are useful because they can travel through certain materials but exposure should be limited because they are harmful to living tissue. Why? High frequency so high energy

  15. Gamma rays are usually naturally produced on Earth by decay of high energy atomic nuclei and produced in space during GRB events.

  16. Isaac Newton passed a beam of sunlight through a prism and discovered the spectrum.

  17. Visible spectrum (visible light): a combination of several different wavelengths of light traveling together. It is the only part of the spectrum we can see with the unaided eye.

  18. short  long  Gamma X-Ray IR UV Radio Visible Micro High f & E low f & E

  19. Notice: as wavelength increases, frequency decreases.

  20. Notice: Shorter wavelengths (higher frequencies) have more energy

  21. All electromagnetic waves move at the same speed in the same medium. Light travels fastest in a vacuum, at the universal constant of c 186,000 mi/s or 3 x 108 m/s Equation: c = f c = speed of light in space f= frequency =wavelength

  22. Does Light Slow Down???For all intents and purposes, the speed of light in our atmosphere is essentially the speed of light in a vacuum. But it is significantly slower in water, for example. So the speed of light is medium dependant. This means that the speed of light only changes if it changes mediums.

  23. When EM Waves Strike Matter…. Three interactions may occurs: • Transmission – medium is transparent to radiation • Absorption - medium opaque to incident radiation • Reflection – process by which incident radiation is bounced off the boundary of a substance.

  24. Reflection Reflection

  25. Reflection is a Boundary Behavior Reflection is the turning back of an electromagnetic wave (or any wave) at the boundary of a substance.

  26. Reflection When a wave strikes a boundary between two media and is bounced back, the wave obeys the law of reflection.

  27. i r Incident Ray Reflected Ray The Law of Reflection The angle of incidence (i) is equal to the angle of reflection (r). (i = r) i is measured from the incident ray to the normal. r is measured from the reflected ray to the normal. 0 90 90

  28. The eye sees the reflected ray, so the image of objects are laterally inverted. Which is the angle of reflection? What is the angle of reflection?

  29. Along with Lasers, Ultrasound and RADAR both use reflection of EM waves to gain information

  30. Specular vs. Diffuse

  31. Incident Rays Reflected Rays Specular Reflection Specular reflection - process whereby incident radiation "bounces off" the surface of substance in a single, predictable direction; caused by surfaces “smooth” (surface irregularities small) relative to wavelengths of incident radiation; no change in velocity or wavelength.

  32. Diffuse Reflection Scattering (diffuse reflection)- occurs when incident radiation is dispersed or spread out unpredictably in many different directions; occurs when surfaces are rough relative to wavelengths of incident radiation; no change in velocity or wavelength

  33. Why Wet Roads Cause Glare Diffuse Reflection light is scattered by rough road surface Specular Reflection light is uniformly reflected in the same forward direction only

  34. Most of What We See is From Diffuse Reflection

  35. Luminous or illuminated? Luminous produces light and illuminated shines by reflected light.

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