chapter 12 light

• The refractive index is the ratio of the speed of light in vacuum to its speed through the medium.
• When white light passes from air into glass, it bends towards the normal because the speed of light decreases as glass is optically denser than air.
• a plane mirror image is the same size as the object, laterally inverted, upright, virtual and its distance from the mirror is equal to the distance of the object from the mirror.
• the angle of incidence = the angle of reflection. (i = r)
• through a converging lens,

  the incident ray passes through the optical centre without bending.

  incident ray parallel to the principal axis is refracted by the lens to pass through the focal point.

  incident ray passing through F is refracted parallel to the principal axis
• a virtual image is an image that cannot be projected on a screen.
• laws of reflection

  • light ray going towards the surface is the incident ray
  • light ray going away from the surface is the reflected ray
  • the perpendicular line to the surface at the point of incidence is the normal
  • the angle between the incident ray and the normal is the angle of incidence (i)
  • the angle between the reflected ray and the normal is the angle of reflection (r)
• laws of reflection

  1. the incident ray, reflected ray and the normal all lie on the same plane
  2. angle of incidence is equal to the angle of reflection
• refraction is the bending of light as it passes from one optical medium to another
• laws of refraction

  1 for two given media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (sin i/sin r = constant)
• thin converging lens

  Principal Axis - line that is passing through the centre of the lens and is perpendicular to the plane of the lens

  Optical Centre, C - point on the principal axis that is midway between the surface of the lens

  Principal Focal Length F - where all rays parallel to principal axis meet after passing through the lens

  Focal Plane

  Focal Length, f - distance between C and F
• thin converging lens

  used for magnifying glasses, cameras, projectors, spectacle lenses