Post on 17-Jan-2018
description
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
NormalLine
r i
Incidentray
Reflectedray
Mirror surface
Angles are ALWAYS measured from the NORMAL LINE
• Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence Angle of reflection
Mirror
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
Angle of incidence = Angle of Reflection For each ray
Dotted lines Shows the Apparent
Ray source
Parallel rays
Reflected rays
RealFocus
Focal length = +Forms real, inverted,Reduced or enlarged
Image. Also formsVirtual, erect,
Enlarged images.
Parallel rays
Reflected rays
Virtual focus
Focal length = -Forms only virtual,
erect, reduced images betweenthe virtual focus and the mirror.
Apparent Convergence of rays
2 f(f)
Focal ray
Parallel rayRay thru 2f
Image is:VirtualErectReducedAppears behind the mirror
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
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
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
Virtual focusFocus = -
Can form only virtual,Erect and reduced
images
Principlefocus
Parallel rays
Focus = +Can form real images(enlarged or reduced
& inverted) orEnlarged virtual images
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.
• We see things because they reflect light into our eyes:
Homework
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
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
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