Transcript Optics - Mr. Gallagher's Physics

Optics
Optics
• Optics is the study of how light behaves.
• Optics also includes the study of the eye itself.
Light Ray
• Light travels in a straight line.
• A light ray is an imaginary line that represents
a thin beam of light.
Optical Devices
• Lenses: bend light in a specific way.
▫ Converging lens (convex): bends light to a
point.
▫ Diverging lens (concave): Spreads light out.
• Mirrors: reflects light
• Prism: can both bend and/or reflect light.
Four Ways Light is Affected by Matter
• The light can go through almost unchanged
(transparency). (Glass, some plastic, etc.)
• The light can go through but be scattered
(translucency). (Tissue paper, frosted glass)
• The light can bounce off (reflection).
• The light can transfer its energy to the material
(absorption).
Specular Reflection
• A ray of light that strikes a
shiny surface (like a
mirror) creates a single
reflected ray. This type of
reflection is called
specular reflection.
Diffuse Reflection
• A surface that is not
shiny creates diffuse
reflection. In diffuse
reflection, a single ray of
light scatters into many
directions
Reflection
• The incident ray is the light ray that strikes the
mirror.
• The reflected ray is the light ray that bounces off
the mirror
• Between the incident and reflected rays, there is an
imaginary line called the normal line which is
perpendicular to the surface of the mirror.
• The angle between the incident ray and the normal
line is called the angle of incidence.
• The angle of reflection is the angle between the
normal line and the reflected ray.
The Law of Reflection
• The law of reflection
says the angle of
incidence equals the angle
of reflection.
Refraction
• Light rays may bend as they cross a boundary
from one material to another.
▫ For example, light waves bend from air to water.
• Refraction is the bending of light rays.
• The index of refraction (n) for a material
measures the ability of the material to bend
light.
• The index of refraction is represented by a
lowercase letter n.
• The angle of refraction is the angle between
the refracted ray and the normal line.
Total Internal Reflection
• Total internal reflection happens when the
angle of refraction becomes greater than 90
degrees
• The angle of incidence at which the angle of
refraction is 90 degrees is called the critical
angle.
▫ The critical angle depends on the index of
refraction of the material.
• Fiber optics are thin glass fibers that use total
internal reflection to carry light, even around
bends and corners