Refraction of Light Flashcards
Define Refraction
change in direction of light when it passes from one transparent medium into another of different optical density. The incident ray, the refracted ray and the normal all lie in the same plane.
What happens when light enters a dense medium from a less dense medium
The more dense the medium the slower the light passes through it. The ray is deviated towards the normal
Refractive index of common materials
Air=1
Water (incl aqueous)= 1.33
Cornea= 1.37
Crystalline lens= 1.386-1.406
Crown glass= 1.52
Flint glass= 1.6
Diamond= 2.5
What is snell’s law
states that the incident ray, refracted ray and the normal all lie in the same plane and that the angles of incidence, i, and refraction, r, are related to the refractive index, n, of the media concerned by the equation
n=sin i/ sin r
where the first medium is a vacuum, n is the absolute refractive index, and in air n is the refractive index.
How to calculate refractive index of ray of light travelling through different density optical medium
water n glass= n glass/ n water
or simply
n2=n2/n1
What happens to a ray of light passing through glass
Light passing obliquely through a plate of glass is deviated laterally and the emerging ray is parallel to the incident ray. Thus the direction of the light is unchanged but it is laterally displaced
How much reflection can occur at every interface
4% roughly
What happens when a ray of light approaches a convex spherical curved surface
causes parallel light to converge to a focus if n2 is greater than
n1, or to diverge as from a point focus if n2 is less than n1
Formula for refracting/vergence power
surface power= n2-n1/r
r is the radius of curvature of the surface in metres according to the sign convention
Surface power is positive for converging surfaces and negative for diverging surfaces
What is the critical angle
The angle of incidence when the angle of refraction is 90 degrees
What is total internal reflection
When the angle of incidence exceeds the critical angle, emerging rays are reflected back into the medium
What optical instruments utilise the principle of total internal reflection
Prisms
Fibre optic cables
Surgical intraocular light source
Which light wavelength is deviated most
Light of shorter wavelength is deviated more than light of longer wavelength, e.g. blue light is deviated more than red. The refractive index of a material is normally taken to mean that for the yellow sodium flame.
What is the dispersing power of a medium
The angle formed between the red and blue light around the yellow. This is not related to the refractive index of the material.
