Ray optics

• Ray Optics or Geometrical Optics considers light as a ray that travels in a straight line
• For each object, there is an image
• Reflection is the phenomenon of changing the path of light without any change in the medium
• Reflection of Light is the returning back of light in the same medium from which it has come after striking a surface
• Laws of Reflection:

  • The angle of incidence is equal to the angle of reflection
  • The incident ray, reflected ray, and normal to the reflecting surface at the point of incidence all lie in the same plane
• Total number of images formed by two plane mirrors inclined at an angle θ with each other is given by
• Reflecting surface of a spherical mirror is a part of a hollow sphere
• Spherical mirrors are of two types:

  • Concave spherical mirror
  • Convex spherical mirror
• Sign Convention:

  • All measurements should be taken from the pole of the mirror
  • Measurements along the direction of the incident ray are positive, and opposite to the incident ray are negative
  • Distances above the principal axis are positive, and below the principal axis are negative
• For a real object, u is negative whereas v is negative for a real image and positive for a virtual image
• Mirror Formula relates the focal length of the mirror to the distances of objects and image from the mirror
• Linear Magnification is the ratio of the size of the image to the size of the object formed by a spherical mirror
• Magnification (m) is negative for a real image and positive for a virtual image
• Refraction is the phenomenon of changing the path of light as it goes from one medium to another
• Laws of Refraction:

  • The incident ray, refracted ray, and the normal to the refracting surface at the point of incidence lie in the same plane
  • The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for the two given media (Snell’s law)
• Total Internal Reflection (TIR) occurs when a ray of light traveling from a denser medium to a rarer medium is incident at an angle greater than the critical angle for the two media
• Principle of reversibility of light states that when the final path of a ray of light after any number of reflections and refractions is reversed, the ray retraces its entire path
• Optical fiber, mirage, sparkling of diamond, totally reflecting prism, etc. work on the principle of total internal reflection
• Lens is a transparent medium bounded by two surfaces, one or both of which are spherical
• Convex or Converging Lens is thicker at the center and thinner at its ends
• Concave or Diverging Lens is thinner at the center and thicker at its ends
• Lens maker’s formula
• Power of Lens is the ability of a lens to converge or diverge the rays of light incident on it
• Power of combination lenses in contact
• Magnification by combination of lenses
• Prism has the property of bending the incident light towards its base
• Dispersion by a Prism is the phenomenon of splitting light into its component colors
• Angular Dispersion produced by a prism for white light is the difference in the angles of deviation for two extreme colors, violet and red