Lectures and laboratories activities on the nature of Physics and
concepts and models in optic:
2. From the mechanism of vision to
the rectilinear propagation of light
Alberto Stefanel
Research Unit in Physics Education
University of Udine
•Which of the following figures describe the mechanism of
vision?
a) b)
c)d)
bulbbulb
bulb
object
object
object
object
eyeeye
eyeeye
lightlight
lightlight Visual rays
bulb
When we close the box with the top….
What do you expect to see, looking from the hole?
Inside a black box there are:a mirrora withe tablea puppetAn hole in the side permit to see inside the box when we cover it with the top
Refraction
Reflection Diffusion
Absorption
Transmission
What happens when the light of a source
illuminate an object?
Light and matter
In these cases the phenomenon
is the reflection:
The light shot an object and
return in the same medium with
a well defined angle
A. Reflection and diffusion
Also in these cases light shot the systems and return in the same medium….but in all direction…..
Diffusion by a reflection process
From “Sunday Afternoon on the Island of La Grande Jatte”
Georges Seurat
(1884-1886)
Oil on canvas
... Diffused riflection by the particles
Of pigment suspended in a transparent
medium
What are the laws underlying the reflection
phenomena?
How work reflection when the surface is curved
(not flat)?
How it is possible to construct the image of an
object reflected by a flat or spherical mirror?
The parallax method
Front vision
The line from the black pin to the red
one individuate the incident direction
Lateral vision
Incident
direction
Find the position where to put the blue
pin to obtain the visual alignement of the
black, red and the image of the blue pins
reflected
direction
mirror
From this point of visualization the black pin, the red
pin and the image of the blue are aligned
The direction of the line from the red and
the blue individuate the reflected direction
The parallax method
Measurement
AH (cm) BH (cm) BH/AH
1.…2,5………………… ………2,3………… ……0,92…
2.…3,5………………… ………3,5………… …....1........
3.…4,5………………… ………4,5………… .……1……..
4.…………………… …………………………… .……………..
5.…………………… …………………………… .……………..
6.…………………… …………………………… ………………
Incident
direction
reflected
direction
mirror
A H B
Incident
direction
reflected
direction
mirror
1 A H B
Incident
directionreflected
direction
mirror
2 A H B
Incident
directionreflected
direction
mirror
3 A H B
A. Stefanel - Ottica 1
Me
diu
m 2
The laws of reflection
SIncident ray
Reflected ray
Medium 1
θi
θr
normal
A) -The incident ray
- The reflected ray
- normal to the surface of
separation the two beams
ARE ON THE SAME PLANE
B) -The angle θi,
- the angle θr
ARE EQUAL
θi = θr
A. Stefanel - Ottica 1
Reflection from a non-flat surface
θi
θr
Applying the laws of reflection points by
points
Normal: direction orthogonal to the
tangent plane to the surface in the
incidence point
Mezzo 1
Mezzo 2