13 lenses

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