Law Of Reflection & Refraction



 Law Of Reflection

Law of reflection

When light meets a boundary(from one medium to another),  the forward propagation by scattering is disrupted. The incident light is now scattered backwards without cancellation, this is reflection.

Law of reflection states that

  • Angle of incident is equal to angle of reflection. θi = θr
  • The incident ray, the normal to the surface and the reflected ray all lay on the same plane called the plane of incidence.

 

Law Of Refraction

Law of refraction
Upon entry into the surface, lateral scattering becomes insignificant and thus forward transmission predominates. However, it is observed that when the incident light is directed an angle to the normal, the ray bends. This effect is called refraction. The bending is essentially due to the difference in speed as the beam travels from one medium to another and that the width of the beam is finite.

Law of Refraction states that

  • $n_{i} \text{sin} \, \theta_{i} = n_{t} \text{sin} \, \theta_{t}$
  • The incident and refracted rays all lie in the same plane of incidence.

 

Total Internal Reflection

Total_internal_reflection
To find the critical angle: $\text{sin} \, \theta_{c} = \frac{n_{t}}{n_{i}}$

800px-TIR_in_PMMA
Total internal reflection in PMMA

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