Transcript Reflection of Light from Plane Surfaces

Pinhole Camera
Reflection of Light from Plane
Surfaces
Both angles are measured from a line
perpendicular to the surface – the “normal” line
N
Smooth Surface Reflection
The angle of incidence i is equal to the
angle of reflection r.
Smooth surface reflection
• “Smooth” as it refers to mirrors means that
variations in the surface are significantly
smaller than the wavelength of light.
• Visible light has wavelengths from 400 to
700 nm
Rough Surface Reflection
• If the surface is not smooth enough the
light will reflect, but rays landing at
different points will reflect at different
angles.
Terminology:
• Smooth surface reflection is called
“specular” reflection.
• Rough surface reflection is called “diffuse”
reflection.
• Examples:
– A mirror exhibits specular reflection
– A sheet of white paper exhibits diffuse
reflection.
Image Formation
• We can locate images by “ray tracing” –
drawing the light rays on paper and
reflecting them using a protractor and a
ruler.
image
eye
Virtural
image
Ray Tracing, continued
• Notice in the diagram that all five rays are
reflected according to the rule.
• The reflected rays are extended, using dotted
lines, to the point where they cross behind the
mirror.
image
eye
Virtural
image
Ray Tracing – finding an image
in a plane mirror
• Draw a perpendicular from image through
plane of mirror
• Draw rays from object to midpoint to eye.
(remember: øi = øf )
• Extend reflected ray as dotted line behind
the mirror, to the first perpendicular
• This is the location of the object
Extended Object Ray Tracing
• Multiple rays can be used to image larger
objects