Light

• First Law of light


  Incident ray, reflected ray and normal ray all lie in the same plane.
• Second Law of light

  Angle of incidence, i is equal to angle of reflection, r.
• Characteristics of mirror image

  -Image is same size as object

  -Image is laterally inverted

  -Image is upright

  -Image is virtual

  -Distance from mirror is equal to distance of object from mirror
• 3 Types of rays

  parallel, convergent and divergent
• Formula of refraction

  1. n= sin i/ sin r
  2. n= c/v
• Refraction is the bending of light as light passes from one optical medium to another.
• When light passes from a medium with a lower refractive index into a higher refractive index, it will bend towards the normal.
• When light passes from a medium with a higher refractive index into a medium with a lower refractive index, light bend away from the normal.
• What happens when a light ray meets a glass prism at an angle of incidence of 30 degrees? Explain why?

  1. Refraction takes place
  2. Light ray travels from an optically less dense medium to more dense medium.
  3. Light ray slows down and bends towards normal.
• Explain why a light ray bend away from normal when it travels from water to air.

  1. Refraction takes place
  2. Light ray travels from an optically more dense medium to less dense medium.
  3. Light ray speeds up and bends towards away.
• Total internal reflection is the complete reflection of light ray inside an optically denser medium at it boundary with an optically less dense medium.
• Total internal reflection condition


  1)Light ray in an optically denser medium strikes its boundary with an optically less dense medium

  2)Angle of incidence must be greater than critical angle of the optically denser medium.
• Formula for total internal reflection

  n= 1/sinc
• Applications of total internal reflection

  1)Optical fibres

  2)binoculars

  3)telescopes
• Why is there no refraction?

  1)Total internal refraction occurs.

  2)Light travels from optically denser to less dense medium.

  3)Angle of incidence is greater than critical angle.
• Explain why diamond sparkles.


  More light rays undergo total internal reflection as critical angle of diamond is smaller than glass. More light rays have angle of incidence greater than critical angle.
• Critical Angle


  The angle of incidence in the optically denser medium for which the angle of refraction in the less dense medium is 90 degrees.