Physics Chapter: Light Reflection and Refraction

Light: Reflection and Refraction

• Light is needed for us to see objects
• Objects reflect light falling on them, allowing us to see them
• Light passes through transparent objects
• Light travels in straight lines, demonstrated by shadows
• Diffraction occurs when light bends around small objects
• Light exhibits wave-like and particle-like properties (explained in higher levels)
• Modern quantum theory unites wave- and particle-like behaviors

Reflection of Light

• Highly polished surfaces (mirrors) reflect most light
• Laws of reflection:
  • Angle of incidence equals angle of reflection
  • Incident ray, normal, and reflected ray lie in the same plane
• Plane mirrors produce virtual, erect images of same size as the object
• Images are as far behind the mirror as the object is in front
• Images are laterally inverted

Spherical Mirrors

• Reflecting surface of spherical mirrors can curve inwards (concave) or outwards (convex)
• Concave: Reflecting surface faces inward, center of sphere (used in torches and search lights)
• Convex: Reflecting surface curves outward (used as rear-view mirrors)

Terms Related to Spherical Mirrors

• Pole (P): Centre of the reflecting spherical surface (lies on the surface)
• Centre of Curvature (C): Centre of the sphere the reflecting surface forms part of (lies outside the surface)
• Radius of Curvature (R): Distance between the pole and the centre of curvature (R=2f)
• Principal Axis: Line passing through pole and centre of curvature (perpendicular to the mirror at the pole).
• Aperture: Diameter of the reflecting surface
• Focal Length (f): Distance between the pole and the principal focus (f = R/2)
• Principal Focus: Point where reflected parallel rays converge (concave) or appear to diverge from (convex)

Image Formation by Spherical Mirrors

• Concave Mirrors:
  • Image characteristics (position, size and nature) depend on object position relative to F, C and P
  • Image can be real (inverted) or virtual (erect)
  • Image can be magnified, diminished or same size
• Convex Mirrors:
  • Always produce virtual, erect, diminished images
  • Image is behind the mirror, smaller than the object

Image Formation Using Ray Diagrams

• Methods for locating image positions including: -A ray parallel to the principal axis reflects through the focus (concave) or appears to diverge from it (convex)
  • A ray through the focus reflects parallel to the principal axis (concave) or heading toward the focus (convex) -A ray through the center of curvature reflects back along the same path

Uses of Spherical Mirrors

• Concave: Torches, headlights, shaving mirrors, dental instruments, solar furnaces
• Convex: Rear-view mirrors in vehicles

Refraction of Light

• Light changes direction when entering a different medium (e.g., from air to water)
• This is called refraction.
• Refraction occurs because different media affect the speed of light
• Refraction is described by Snell's Law (ratio of sines of incidence and refraction is constant, for given light and media)

Refractive Index

• Ratio of speed of light in a medium to the speed of light in a vacuum (or air)
• Optically denser medium has a higher refractive index

Refraction through a Rectangular Glass Slab

• Light bends towards the normal when entering a denser medium and away from the normal when exiting
• Emergent ray is parallel to the incident ray but is shifted slightly.
• The refractive index relates to the speed of light in different media

Refraction by Spherical Lenses

• Lenses are transparent materials bound by one or more spherical surfaces.
• Convex lenses converge light (converging lenses)
• Concave lenses diverge light (diverging lenses)
• Key lens parts are:
  • Optical center: Center point on a lens through which light passes without deflection
  • Principal axis: Line through the centers of curvature
  • Principal foci: Points where parallel light rays converge (convex) or seem to diverge (concave)

Image Formation by Lenses

• Convex and concave lenses produce different image characteristics based object position and focal length.
  • Convex lens : Image can be real (inverted) or virtual (erect) and can be magnified, diminished, or same size as the object.
  • Concave lens: Always produces virtual, erect, and diminished images.

Sign Conventions

• New Cartesian Sign Convention uses a consistent system for defining positive and negative distances for object and image positions related to the principal axis.

Mirror and Lens Formulas

• Mirror Formula: 1/u + 1/v = 1/f
• Magnification Formula (Mirrors and Lenses): m = -v/u = h'/h