light , mirrors, and lenses
DESCRIPTION
Properties of Light Light travels in straight lines. Light travels ~ 300,000 km/s Reflection – bouncing back (mirrors) Refraction – bending due to different mediums (lenses) LaserTRANSCRIPT
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Properties of Light
Light travels in straight lines.Light travels ~ 300,000 km/sReflection – bouncing back (mirrors)Refraction – bending due to different
mediums (lenses)
Laser
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NormalLine
r i
Incidentray
Reflectedray
Mirror surface
Angles are ALWAYS measured from the NORMAL LINE
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• Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence Angle of reflection
Mirror
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Clear vs. Diffuse Reflection
• Smooth, shiny surfaces have a clear reflection:
Rough, dull surfaces have a diffuse reflection.
Diffuse reflection is when light is scattered in different directions
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Angle of incidence = Angle of Reflection For each ray
Dotted lines Shows the Apparent
Ray source
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Parallel rays
Reflected rays
RealFocus
Focal length = +Forms real, inverted,Reduced or enlarged
Image. Also formsVirtual, erect,
Enlarged images.
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Parallel rays
Reflected rays
Virtual focus
Focal length = -Forms only virtual,
erect, reduced images betweenthe virtual focus and the mirror.
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Apparent Convergence of rays
2 f(f)
Focal ray
Parallel rayRay thru 2f
Image is:VirtualErectReducedAppears behind the mirror
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Parallel rays
Reflected rays
Virtual focus
Focal length = -Forms only virtual,
erect, reduced images betweenthe virtual focus and the mirror.
Dotted lines Shows the ApparentRay focus
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2. RefractionRefraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a ruler is placed in water it looks like this:
In this case the light rays are slowed down by the water and are _____, causing the ruler to look odd. The two mediums in this example are ______ and _______.
Words – speed up, water, air, bent
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NormalLine
NormalLine
i
r i
r
Glassn = 1.5
Airn =1.0
r = angle of refraction
i = angle of incidence
Light travels more slowlyin glass than air and
bends towards the normalwhen entering glass from air
Light moving fromglass to air
increases speedand bends awayfrom the normal
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Virtual focusFocus = -
Can form only virtual,Erect and reduced
images
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Principlefocus
Parallel rays
Focus = +Can form real images(enlarged or reduced
& inverted) orEnlarged virtual images
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Which color refracts most leaving the prism? The least?
Colored light is made from white light by REFRACTION, but we see color because of REFLECTION.
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• We see things because they reflect light into our eyes:
Homework
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Adding colors• White light can be split up to make separate colors. These
colors can be added together again.
• The primary colors of light are red, blue and green:
Adding blue and red makes magenta (purple)
Adding blue and green makes cyan (light blue)
Adding all three makes white
again
Adding red and green makes yellow
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Seeing color• The color an object appears depends on the colors of light
it reflects.
For example, a red book only reflects red light:
White
lightOnly red light is
reflected
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A white hat would reflect all seven colors:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):
Purple light
White
light