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Light
Chapter 18
Section 1 - Light and Color
When light strikes an object, the light ca
be reflected, transmitted, or absorbed.
Transparent - a material that transmits
most of the light that strikes it
Translucent - a material that scatters
light as it passes through
Opaque - a material that reflects or
absorbs all of the light
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Light and Color
The color of an object depends on the
object’s material and the color of the
light striking the object.
Every object absorbs some
wavelengths of light and reflects others.
The color of an opaque object is the
color of the light it reflects.
The color of a transparent or translucent
object is the color of the light it
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transmits.
Light and Color
Primary colors – three colors that can
combine to make any other color
– red, green , blue
Secondary colors – produced when two
primary colors combine in equal
amounts
– magenta, yellow, and cyan
White light – produced when the three
primary colors are combined in equal
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amounts.
Light and Color
Complementary colors – any two colors
that combine to form white light.
Pigments – colored substances that are
used to color other materials
– As pigments are added together, fewer
colors of light are reflected and more
absorbed.
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Section 2 - Reflection and
Mirrors
light rays represent light waves as
straight lines
The two ways in which a surface can
reflect light are regular reflection and
diffuse reflection pg.618
Regular – when parallel rays of light hit
a smooth surface
Diffuse - when parallel rays of light hit a
bumpy or uneven surface
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Reflection and Mirrors
Plane Mirror
Plane mirror – a flat sheet of glass that
has a smooth, silver-colored coating on
one side
image - copy of an object formed by
reflected or refracted rays of light
produces a virtual image
– right side up
– the same size as the object being reflected
– behind the mirrorChapter 18
Reflection and Mirrors
Concave Mirrors
Surface curves inward like a bowl
– used for make-up mirrors
Optical Axis – an imaginary line that divides a
mirror in half (equator)
Focal Point – the point at which rays parallel
to the optical axis meet.
Ray Diagram
Forms either a virtual image or real image
(pg. 621)
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Reflection and Mirrors
Concave Mirrors
Real Image – forms when rays actually
meet
– Upside down
– Larger or smaller than the object
Image
– Real - farther than the focal point
• In front and upside down
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Reflection and Mirrors
Concave Mirrors
Image (Cont’d)
– Virtual - Closer than the focal point
• Behind and upright
At the focal point - no image is formed
– Forms parallel light rays
– Headlights
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Reflection and Mirrors
Convex Mirrors
Surface curves outward.
Forms a smaller virtual image (pg. 622)
– used for security or blind spots on roads
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Section 3 - Refraction and
Lenses
When light rays enter a medium at an
angle, the change in speed causes the
rays to bend, or change direction
– Two images in fish tank
index of refraction - a measure of how
much a ray of light bends when it enters
that material (pg. 624)
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Refraction and Lenses
Prisms and Rainbows
– Longer wavelengths (red) refracted less
– Shorter wavelengths (violet) refracted more
– Separates the colors of white light
mirage - an image of a distant object
caused by refraction of light (by hot air)
Lens – a curved piece of glass or other
transparent material that is used to
refract light
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Convex lens
Thicker in the center than at the edges
parallel light rays are bent towards the
center of the lens (pg. 626)
forms virtual or real image dependent
upon position relative to the focal point
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Concave lenses
Thicker at the edges than in the center
parallel light rays are bent away from
the center of the lens (pg. 627)
forms virtual image (again because rays
can never meet)
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Section 4 - Seeing Light
You see an object when a process
occurs that involves both your eyes and
your brain.
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Section 4 - Seeing Light
Eye picture pg. 631
– cornea – pupil – iris – lens – retina – optic nerve Chapter 18
Seeing Light
nearsighted - can see close objects clearly
– eyeball too long.
– corrected with concave lens
Farsighted - can see far away objects clearly
– eyeball too short.
– Corrected with convex lens
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Section 5 - Using Light
Optical Instruments
– Telescope uses lenses or mirrors to collect
and focus light from distant objects.
– Images are upside-down
• Refracting telescope
– Objective
– Eyepiece
• Reflecting
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Using Light
Optical Instruments
– (Light) Microscope – uses a combination of
lenses to produce and magnify an image
– Camera – use a lens to focus light to form
a real, upside-down image on the back of
the (film) camera
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Using Light
– Lasers
• Light amplification by stimulated emission of
radiation
• Laser light consists of light waves that all have
the same wavelength, or color. The waves are
coherent, or in step.
• Uses
– Compact discs
– Holography
– Surgery
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Using Light
– Optical Fibers – long, thin strands of glass
or plastic that can carry light for long
distances without allowing the light to
escape.
• Total internal reflection – complete reflection of
light by the inside surface of the medium
• Medicine
• Communication
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