2. 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.
3. 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
4. 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
5. The Law of Refraction
1. 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.
7. 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
9. Physics and Contact Lenses
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.
10. 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.
13. 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.
14. 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
