Download Sect.3

Ch. 2.3
REFLECTION AND
REFRACTION
Reflection
Reflection occurs when an object or wave
bounces back off a surface through which
it cannot pass
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Law of reflection: the angle of incidence
equals the angle of reflection
Mirrors
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Plane mirrors – flat sheet of glass that has
a smooth, silver-colored coating on one
side.
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Image – copy of an object formed by reflected
or refracted rays of light
Virtual image – an upright image that forms
where light seems to come from. Your image
appears to be behind the mirror.
Mirrors cont’d
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Concave mirrors - a mirror with a surface
that curves inward like the inside of a bowl
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Optical axis – imaginary line that divides a
mirror in half
Focal point – the point at which rays parallel
to the optical axis meet or converge
Real image – forms when rays actually meet.
Virtual images formed by a concave mirror
are always larger than the object.
Mirrors cont’d
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Convex Mirrors – a mirror with a surface
that curves outward.
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Convex mirrors can NEVER create a real
image
Ex: security mirrors and safety mirrors in
banks, parking garages.
Allows you to see a larger area than you can
with a plane mirror.
Refraction
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Light travels in straight lines IF the medium it
travels through does not change.
If light enters the new medium perpendicular to
the boundary, it will keep moving in the same
direction
If it hits the boundary at an angle, it will bend. –
bending of light waves due to a change in speed
is called the refraction.
Refraction cont’d
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Refraction in different mediums
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When light rays enter a medium at an angle,
the change in speed causes the rays to bend,
or change direction.
Diff. Densities within the same medium can
cause refraction as well. EX. Air heated by a
campfire can cause objects to appear
shimmer. Stars twinkle due to variations in
the atmosphere density.
Refraction cont’d
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Effects of refraction – separation of visible
light into its component colors by a prism.
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Difference in refractions causes white light to
spread out into the colors of the spectrum :
ROYGBIV
Water droplets can cause the same effect –
rainbow
Pencil in a glass
Lenses
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Lens is a curved piece of glass or other
transparent material that refracts light.
The type of image formed by a lens
depends of the shape of the lens and the
position of the object.
Lenses cont’d
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Convex lenses – (magnifying glass)
thicker in the center than at the edge.
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An object’s position relative to the focal point
determines whether a convex lens forms a
real image or a virtual image. (see fig 19, pg.
59)
Lenses cont’d
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Concave lenses
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Concave lens is thinner in the center than at
the edges.
A concave lens can produce only virtual
images because parallel light rays passing
through the lens never meet.