Light

Light

  • Light is a form of electromagnetic radiation that can be detected by the human eye.

Reflection

Basics of Reflection

  • Perpendicular: The normal line is perpendicular to the surface at the point of incidence.

  • Incident Ray: The ray of light that strikes the surface.

  • Reflected Ray: The ray of light that bounces off the surface.

Types of Reflection

Diffused Reflection

  • Occurs when light reflects from a rough surface at many angles.

  • Results in scattered light, making surfaces look less shiny.

Specular Reflection

  • Occurs when light reflects from a smooth surface at just one angle, like a mirror.

  • Examples include moonlight reflecting from a lake.

Properties of Real and Virtual Images

Real Images

  • Formed by the actual intersection of light rays after encountering a mirror.

  • Always located in front of the mirror.

  • Can be projected onto a screen and is always inverted.

Virtual Images

  • No light passes through the apparent location of the image; formed behind the mirror.

  • Cannot be projected onto a screen and is always upright.

Plane Mirrors

  • High polish surface producing images through regular reflection.

  • Common type is a glass plate silvered on one side, with a reflectance of about 85%.

  • Reversal effect: Right side of the object appears as the left side in the image.

  • The distance of the image from the mirror equals the distance of the object from the mirror, creating a virtual, erect, same-size image.

Curved Mirrors

Curved Mirror Anatomy

  • Reflecting surface is part of a large sphere.

  • Types include:

    • Concave Mirror: Curves inward, used to magnify objects; creates convergent rays.

    • Convex Mirror: Curves outward, reflects parallel rays outward; acts as a diverging mirror.

Ray Diagram Rules for Curved Mirrors

Concave Mirror

  • Draw the principal axis and mark the position of the focus and center of curvature.

  • The distance from the vertex to the center of curvature is the radius, and from vertex to focus is the focal length.

  • The image can be determined using ray diagrams:

    • Draw a horizontal line for the principal axis.

    • Draw object rays from the object tip to illustrate the direction.

Convex Mirror

  • Similar diagram rules as for concave, but rays diverge after reflection.

  • The image formed is virtual, upright, and reduced in size.

Mirror Equations

  • Mirror Equation: Relates object distance (do), image distance (di), and focal length (f).

  • Magnification Equation: Relates the height of the image to the height of the object.

Sign Conventions

  • Focal Length (f):

    • Positive for concave mirrors.

    • Negative for convex mirrors.

  • Image Distance (di):

    • Positive for real images on the object’s side.

    • Negative for virtual images behind the mirror.

  • Image Height (hi):

    • Positive for upright images.

    • Negative for inverted images.

Practical Applications

  • Use of concave mirrors in shaving mirrors, makeup mirrors, and telescopes.

  • Convex mirrors used in vehicle side mirrors for a wider field of view.

Sample Problem (for practice)

  • A 4.00-cm tall light bulb placed 45.7 cm from a concave mirror with a focal length of 15.2 cm requires determining the image distance and size.