Color, Plane Mirrors, and Thin Lenses

Color and Dispersion

  • White light is a mixture of all colors.
  • The index of refraction of a transparent material varies slightly for different colors of light.

Rainbow Formation

  • Rainbows are formed through refraction, reflection, and refraction of light in raindrops.
  • Process:
    1. Sunlight enters a raindrop.
    2. Dispersion occurs, causing different colors to refract at different angles.
    3. Some light reflects back inside the drop.
    4. Dispersion further separates colors as light refracts back into the air.
  • Red light is refracted at approximately 42.5∘42.5^\circ, coming from higher drops.
  • Violet light is refracted at approximately 40.8∘40.8^\circ, coming from lower drops.

Colored Objects

  • An object appears green because it reflects green light and absorbs other colors.

Image Formation in Plane Mirrors

Key Concepts

  • Virtual Image: The image formed by a plane mirror is a virtual image, not a real image. Virtual images cannot be caught on a screen because they are formed by the imaginary intersection of light rays.
  • Image Location: The image appears to be as far behind the mirror as the object is in front of it.
  • Magnification: The image is unmagnified; the image height is the same as the object height.
  • Orientation: The image is upright, maintaining the same orientation as the object.

Ray Diagrams

  • Ray diagrams are used to illustrate image formation in plane mirrors.
  • Incident rays, reflected rays, and normals are important components in ray diagrams.
  • Simulations (e.g., oPhysics) can be used to explore image formation in plane mirrors.

Real vs. Virtual Images

  • A real image can be projected onto a screen, whereas a virtual image cannot.
  • Real images are formed by the actual intersection of light rays.
  • Virtual images are formed by the imaginary intersection of light rays.

Plane Mirror Characteristics

  • Image Location: Opposite side of the mirror, same distance from the mirror as the object.
  • Orientation: Upright (same as the object).
  • Size: Same size as the object.
  • Type: Virtual.

Visibility

  • Whether a person can see another person in a mirror depends on the angles of incidence and reflection.

Thin Lenses

  • Lenses use refraction at curved surfaces to form images from light rays.

Types of Lenses

  • Converging Lens: Curved outward; converges light to a single focal point behind the lens; thickest in the middle.
  • Diverging Lens: Curved inward; diverges light from a focal point in front of the lens; thickest at the edges.

Focal Length

  • The focal length of a lens depends on its shape. A more curved lens has a shorter focal length.

Schedule

  • Upcoming Topics: Total Internal Reflection, Thin Lens (Ray Diagram), Thin Lens (Lens Equation).
  • Quizzes:
    • Quiz 10 (April 28): Thin Lens (Ray Diagram)
    • Quiz 11 (May 5): Spherical Mirror
    • Quiz 12 (May 12): Summary
  • Labs:
    • Lab 11: Ray Optics (Reflection and Refraction)
    • Lab 12: Thin Lenses
  • Final Exam: May 21

Reminders

  • Homework due Thursdays at 11:59:00 pm.
  • Visit office hours for help.