Refraction of light

definition

refraction

refraction is the bending of light as it passes from one medium to another medium of different optical density

incident ray

light ray that hits the reflecting surface

refracted ray

light ray that enters the medium and undergoes change of direction

point of incidence

point at which the incident ray hitd the reflecting surface

normal

imaginery line that is perpendicular to the reflecting surface at the point of incidence

angle of incidence

angle between the incident ray and normal

angle of refraction

angle between the refracted ray and the normal

why and how refraction occurs

optically dense to less dense medium

  • speed of light increases

  • bends away from normal

optically less dense to denser medium

  • speed of light decreases

  • bends toward the normal

f - faster

a - away

s - slower

t - toward

refractive index

  • refractive index is the ratio of the speed of light in vacuum to the speed of the light in medium

  • n=cvn=\frac{c}{v}

laws of refraction

  • the incident ray, refracted ray and the normal at the point of incidence all lie on the same plane

  • for two given media, the ratio of the sine of the angle of incidence to the sine of the angleo of refraction is a constant

  • n=sin⁡θairsin⁡θmediumn=\frac{\sin\theta air}{\sin\theta medium}

  • refractive index of air is n=1.0n_{}=1.0

total internal reflection

  • the light ray is directed towards the centre of the glass block

  • when the light ray crosses both boundaries perpendicularly, the angle of incidence is 0 and there is no refraction

  • as the ray box is moved clockwise, there is refraction and partial reflection

  • at a particular angle of incidence θ\theta , the angle of refraction is 90o90^{o}

  • θc\theta_{c} is known as the critical angle

  • when the angle of incidence is greater than the critical angle, the light ray will be completely reflected off the flat surface of the glass block

  • total internal reflection is the complete reflection of light inside an optically denser medium at its boundary with an optically less dense medium

critical angle

critical angle is defined as the angle of incidence in an optically denser medium for which the angle of refraction in the optically less medium is 90o90^{o}

  • sin⁡θc=1n\sin\theta_{c}=\frac{1}{n}

conditions for total internal reflection

  • incident ray must travel from an optically denser medium to an optically less dense medium

  • angle of incidence must be greater than the critical angle

applications

  • optical fibres

    • telecommunication

      • data transfer rate is ten to thousands of times faster as compared to using copper wires

      • there is less signal loss compared to copper wires

      • optical fibres are lighter and cheaper as compared to copper wires of the same length

      • carry much more information over long distances

      • immune to electromagnetic interference

    • medicine

      • thin and light - endoscopes are kept small for minimally invasive examination and surgery

      • flexible - endoscopes can curve around obstacles when taking images inside the body