LENSESREFRACTION AND TIR
Refraction (Ray Property)
• REFRACTION is the change of direction of light when it passes from one medium to another or of different optical density.
• Optical density has something to do with the transparency of a substance to light. Light travels slowly in an optically dense medium.
Index of Refraction (n)
• - property of a substance which refers to ratio of the speed of light in a vacuum ( c ) to the speed of light in the substance
• OPERATIONAL DEFINITION: n = c / v where: c = 3 x 108 m/s and v is
the velocity of light in the medium
Example Table
Index of Refraction of Some Materials ( for Yellow light ):
Materials n Materials n
air 1.0003 glass (crown) 1.5230
ice (at 0°C) 1.3090 sapphire 1.7700
water 1.3300 zirconium 2.2000
fused quartz 1.4600 diamond 2.4190
The Law of Refraction1. The incident ray, refracted ray and the
normal line lie in one plane.2. When a ray of light passes obliquely
from an optically dense medium, it is refracted away from the normal line.
3. When a ray of light passes obliquely from an optically less dense medium, it is refracted toward the normal line.
4. At perpendicular incidence, no bending of light ray occurs.
Snell’s Law Visualization
Spherical Lens- any piece of glass or transparent material
having at least one spherical surface
Types:1. Convex Lenses – lenses that are thicker at
the middle than at the edges; also called converging lenses
2. Concave Lenses – lenses that are thicker at the edges than at the middle; also called diverging lenses
Specific Lens Types
Myopia (Nearsightedness) occurs when light rays are focused in front of the retina. Close objects can be seen clearly but objects at a distance are out of focus. Lenses
that are thinner in the center than on the edges (concave) increase the focal length.
Physics and Contact Lenses
Hyperopia (Farsightedness) is a condition in which light rays are focused behind the retina. Distant objects can be seen clearly but close objects are out of focus. Lenses that are thicker in the center than on the edges
(convex) decrease the focal length.
Physics and Contact Lenses
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White Light Refraction
Total Internal Reflection• When light passes from a dense substance into a less dense
substance, there is an angle, called the critical angle, beyond which 100 percent of the light is reflected from the surface between substances.
• Total internal reflection occurs when light strikes the boundary between substances at an angle greater than the critical angle.
The Law of Refraction
Snell’s Law (Willebrord Snell) :
n1sinθi = n2sinθR
where: n1 - index of refraction of the 1st medium
n2 - index of refraction of the 2nd medium
θi - is the angle of incidence
θr - is the angle of refraction