Optics

  • Reflection : Bouncing back of light from a surface.
  • Laws of Reflection:
    • Angle of incidence = Angle of reflection
    • Incident ray, reflected ray, and normal lie in the same plane
  • Refraction : Bending of light when it passes from one medium to another due to change in speed.
  • Snell’s Law : Expresses relation between angle of incidence 𝑖  and refraction 𝑟 .
    • n1 ​sin i=n2 ​ sin r
    • n = sin r / sin i​
  • Refractive Index : Ratio of speed of light in vacuum (𝑐) to that in the medium (𝑣 ) .
    • 𝑛 = 𝑐 / 𝑣 
  • Critical Angle : Angle of incidence in denser medium for which angle of refraction is 90°.
  • Total Internal Reflection 
    • Occurs when:
      • Light travels from denser to rarer medium.
      • Angle of incidence > critical angle.
    • Applications: Optical fibers, mirage.
  • Scattering : Deviation of light from its path due to interaction with small particles.
    • Rayleigh scattering: Explains blue sky and red sunset.
  • Dispersion : Splitting of white light into its component colors (VIBGYOR).
    • Seen in prism or rainbow formation.
  • Diffraction : Bending of light around corners or narrow slits.
    • More prominent for waves with larger wavelength.
  • Polarization : Restriction of vibrations of light to one direction.
    • Only transverse waves like light show polarization.
  • Interference : Superposition of two coherent light waves.
    • Types:
      • Constructive: Bright fringe
      • Destructive: Dark fringe
  • Mirror
    • Plane Mirror :
      • Image: Virtual, erect, same size, laterally inverted.
    • Concave
      • Can form real/inverted or virtual/erect images depending on object distance.
    • Convex
      • Image: Always forms virtual, erect, and diminished images.
    • Mirror Formula
      • f = focal length
      • v = image distance
      • u = object distance
    • Magnification
      • For mirrors: 𝑀 = − 𝑣/𝑢
        • M>1: Magnified
        •  M<1: Diminished
    • Sign Convention
      • All distances measured from pole (P) of mirror/lens.
      • Left side of mirror: Negative
      • Right side: Positive
      • Above principal axis: Positive
      • Below: Negative
  • Lens
    • Concave (Diverging):
      • Always forms virtual, erect, and diminished images.
    • Convex (Converging):
      • Can form both real and virtual images.
      • Used in magnifying glass, camera.
  • Microscope : viewing very small objects.
    • Compound microscope uses two lenses: Objective + Eyepiece.
  • Telescope
    • Used to view distant objects.
    • Astronomical Telescope: Uses convex lenses or mirrors.
  • Human Eye Parts
    • Cornea: Outer layer, helps focus.
    • Iris: Controls pupil size.
    • Pupil: Allows light entry.
    • Lens: Focuses light on retina.
    • Retina: Converts light to nerve signals.
    • Optic Nerve: Sends signals to brain.
  • Eye Related Diseases
    • Myopia (Near OR Short sightedness): Corrected with concave lens.
    • Hypermetropia ( Long or Far sightedness): Corrected with convex lens.
    • Presbyopia: Age-related, needs bifocal lenses.
    • Cataract: Clouding of eye lens.
Optics