Transcript Document

• Real vs Virtual
– Real Images can be seen on a piece of paper or screen
placed because the focal point is in front of the mirror
or behind the lens.
– Virtual Images can not be seen on a piece of paper or
screen, because the focal point is behind the mirror or
in front of the lens. Virtual images are images which are
formed in locations where light does not actually reach;
it only appears to an observer as though the light were
coming from this position.
• Inverted vs Upright
– Inverted images are upside-down.
– Upright images are right-side up.
• Smaller, Larger, or Same Size
– Smaller Images are reduced in size compared to
the actual object.
– Larger Images are enlarged in size compared to
the actual object.
– Same Size Objects are unchanged in size
compared to the actual object.
• Size is also discussed quantitatively in
terms of Magnification.
Light follows the same law of reflection as all
other waves.
Both angles are measured from the normal to the
surface at the point of incidence.
Glare- bright light that reflects to your eyes from the
surface of smooth objects
Diffuse vs Regular Reflection
• Diffuse reflection is produced when the rays
are reflected in many different directions by
an uneven surface.
• Regular reflection is produced by a very
smooth, flat surface. The rays leave the
surface parallel to each other.
Plane Mirrors
• uniformly flat. The image is sent back
virtual, erect, same size, and laterally
•The image of the object
looks like it is the same
distance in back of the
mirror as the actual object
is in front of the mirror.
Types of Curved Mirrors
– Concave (CONVERGENT)
• focus the light at a point in front of the mirror.
• reflect light from the inner surface.
– Convex (DIVERGENT)
• spread the light out.
• reflect light from the outer surface.
Features of Curved Mirrors
• Principal Axis: the straight line perpendicular to the surface of the
mirror at its center.
• Focal Point: the location where the parallel rays of light from the
source meet, or converge.
• Focal Length: the distance from the Focal Point to the mirror along
the Principal Axis.
• Center of Curvature: twice the distance of the focal point to the
mirror surface.
• Vertex: point where principal axis meets mirror
A Concave Mirror
The image formed is dependent
upon where the object is located
relative to the focal point of the
concave mirror.
3 rules
• Incident ray parallel to P.A will reflect
through focus
• Incident ray through focus will reflect
parallel to P.A.
• Incident ray through Center of Curv.
will reflect back on self
– Don’t forget regular incidence=reflection
from vertex
Locate an image
• Use at least 2 lines through object
• Image found where
– Reflected lines cross
– Virtual extensions of virtual lines (behind
mirror) cross
The change in direction or bending of light
at the boundary between two media.
Refraction only occurs when the angle of incidence
is non-zero.
Optical Density
• The optical density of a material relates to
the sluggish tendency of the atoms of a
material to maintain the absorbed energy of
an electromagnetic wave.
• The more optically dense which a material
is, the slower that a wave will move through
the material.
From less dense to more dense: light
travels more slowly and the angle of
refraction is smaller than the angle of
FST = Fast to Slow, Towards Normal
From more dense to less dense: light
travels more quickly and the angle of
refraction is greater than the angle of
SFA = Slow to Fast, Away From
Practice Refraction
Two Criteria for Total Internal
Reflection (T.I.R.)
1. Light must pass from a more optically
dense to less optically dense medium.
2. There are only specific angles of incidence,
called the critical angle, which is different
for each medium.
Increasing Angle of Incidence
An Application of T.I.R.
Fiber optics.
Telephone, radio,video, and television
signals can now be sent with light beams
rather than electric currents.
This is more energy-efficient.
Demonstrations of T.I.R.
Why are different colors
• The shorter the wavelength, the more the
light slows down when entering a new
• Violet has the shortest wavelength, so it
slows down the most and bends the most.
Why are skies blue?
• The two most common types of matter
present in the atmosphere are gaseous
nitrogen and oxygen.
• These are most effective in scattering
the higher frequency portions of the
visible light spectrum
• violet light is scattered most easily,
followed by blue light, green light, etc
• White light (ROYGBIV) passes through
our atmosphere
• High frequencies (BIV) become
scattered by atmospheric particles
• Lower frequencies (ROY) are most likely
to pass through the atmosphere without
a significant alteration in their direction
• the skies are illuminated with light on
the BIV end of the visible spectrum.
• Thus, we view the skies as being blue in
Why Are Sunsets Red?
• As the sun
approaches the
horizon line,
sunlight must
traverse a greater
distance through
our atmosphere;
this is
demonstrated in
the diagram.
• As the path which sunlight takes through our
atmosphere increases in length, ROYGBIV
encounters more and more atmospheric particles.
• There is greater and greater amounts of yellow
light scattered, leaving concentrations of red and
orange frequencies of light.
• Thus, sunsets have a reddish-orange hue.
• The more particles in the atmosphere (clouds,
pollution, etc.), the more pronounced the effect of
a red sunset.