Transcript 2.3: Reflection and Refraction

7.6.c Students know light travels in straight lines
if the medium it travels through does not
change.
7.6.g Students know the angle of reflection of a
light beam is equal to the angel of incidence
When an object or wave hits a surface through
which it cannot pass, it bounces back.
Angle of incidence- Angle
between the incoming wave
and the normal
Angle of reflection- angle
between the reflected wave
and the normal
Key concept: The law of reflection states that the angle
of incidence equals the angle of reflection.
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Light travels in
straight lines unless
the medium it is
traveling through
changes
When light hits a
shiny surface it
bounces back
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Image- copy of an
object formed by
reflected or refracted
rays of light
Optical axis- an
imaginary line that
divides a mirror in
half
Focal point- point
where rays parallel to
the optical axis meet
or converge
Mirrors: Plane Mirrors
•Plane mirror- flat sheet of glass
that has a smooth, silver-colored
coating on the one side
•Image appears to be as far
behind the mirror as the object
is in front of the mirror
•The reflected light from an
object looks as through it came
from a point behind the mirror
•Creates a virtual image that is
upright and same size- but not
quite the same
•Virtual imageupright image that
forms where light
seems to come from
(image appears
behind mirror)
Real
Virtual
•Real image- forms
when rays actually
meet
A mirror with a surface that curves inward like the
inside of a bowl is a concave mirror.
Reflects rays that are parallel back through the focal point
Mirrors: Concave Mirrors
Concave mirrors can form either virtual
images or real images.
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The location of the focal
point depends on the
shape of the mirrors
Concave mirrors can
either be can be either
virtual or real
Virtual images formed
by a concave mirror
are always larger than
the image
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Object in mirror are closer than
they appear
Can never create a real image
because the rays never meet
Disadvantage: image is reduced
in size- appears to be further
away than it is
Advantage: allows you to see a
larger area than you can with a
plane mirror
Where they are used: security,
passenger side mirrors, safety
mirrors in banks, parking
garages, offices
A mirror with a surface that curves outward is
called a convex mirror.
Key Concept: When light rays enter a medium
at an angle, the change in speed causes the
rays to bend, or change direction.
Light travels in
straight lines if the
medium does not
change
If light enters a
new medium it
might slow down
or speed up
•Different densities in
the same medium cause
refraction
•Stars twinkle because
of variations in the
density in the Earth’s
atmosphere
•Rainbows are a pretty effect caused by refraction- it is
the separation of the visible light
•The longer the wavelength the less the wave is bent by a
prism
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Lens- a curved piece of
glass or other
transparent material
that refracts light
A lens forms an image
by refracting light rays
passing through it
The type of image
formed depends on the
shape of the lens and
the position of the object
Focal length- the
distance from the lens to
the focal point
Key Concept: An object’s position relative to the focal
point determines whether a convex lens forms a real
image or a virtual image.
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Convex lens- thicker in the center than the edge
Key concept: A concave lens can produce only virtual
images because parallel light rays passing through the
lens never meet.
Concave lens- thinner in the center than the edges