AP Night Lecture #3: Optics, Part I

Online Video Lessons:

For animated lessons with narration and problems, visit HippoCampus's AP Physics B II website and scroll down to the "Physical Optics" and "Geometric Optics" topics.

Applet Trouble? If you have trouble running the applet below, visit www.java.com to download and install the latest version of Java onto your computer.
  1. Electromagnetic spectrum
    1. Light is an electromagnetic wave (or sometimes acts as a particle: the photon)
    2. Categories of light arranged in a spectrum of decreasing wavelength (and thus increasing frequency)
      1. radio
      2. microwave (communication, radar, cooking)
      3. infrared (heat)
      4. visible light (you must memorize that visible λ between 400 nm and 700 nm)
      5. ultraviolet (tanning, germicidal)
      6. X-rays
      7. Gamma (γ) rays
      8. Electromagnetic spectrum graphic
  2. Reflection
    1. The angle between an incoming ray and the normal to a reflective surface is the angle of incidence.
    2. The angle between a normal to a reflective surface and the outbound ray is the angle of reflection.
    3. The angle of incidence equals the angle of reflection (if it comes in at 20°, it leaves at 20° from the other side of the normal line).
    4. Mirrors
        5. Plane mirrors form erect, virtual, normal-size images behind themselves.
      1. Convex mirrors always form erect, virtual, reduced images behind themselves.
      2. Concave mirrors form various image types as predicted by the ray diagram procedure:
        1. Draw the mirror, locate its center of curvature and the focal point will be halfway between them.
        2. Draw the object as an upright arrow at its location relative to the focal point and center of curvature.
        3. Draw a light ray that passes through the top of the object and the focal point; it will bounce off the mirror parallel to the principal axis.
        4. Draw a light ray that passes through the top of the object and goes straight toward the mirror, parallel to the principal axis. It will reflect so that it passes through the focal point.
        5. The image forms where the two reflected rays intersect, and can be drawn as an arrow starting there and proceeding to the principal axis.
        6. Concave Mirror Ray Diagrams Java Applet (drag the red upright "object" arrow around)
        7. Convex Mirror Ray Diagrams Java Applet (drag the red upright "object" arrow around)
  3. Mirror/Lens Math
    1. If f=focal length (and is negative for convex mirrors and concave lenses that diverge light instead of physically focusing it), si=distance from image to mirror/lens, and so=distance from object to mirror/lens, then 1/f = 1/si + 1/so
    2. If hi=height of image and ho=height of object, then hi / ho = -si / so
      (and negative hi indicates an inverted, and thus real, image)

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