Download Optics, IDC202

Optics, IDC202
Lecture 5.
Rejish Nath
Contents
Literature:
1. Optics, (Eugene Hecht and A. R. Ganesan)
2. Optical Physics, (A. Lipson, S. G. Lipson and H. Lipson)
3. Optics, (A. Ghatak)
Ray optics
screen
slit
w
o
d
a
h
ical s
r
t
e
m
Geo
Geom
etrica
l shad
ow
If the wave length of the light is much small compared to the slit
width or the radius of a circular aperture, we have well-defined
boundaries.
Ray optics
screen
slit
w
o
d
a
h
ical s
r
t
e
m
Geo
Geom
etrica
l shad
ow
What happened if I reduce the slit width???
What happened if the wavelength of a light is taken to be zero???
(Geometrical or ray optics)
Ray optics
In a homogeneous medium light ray travels in straight line.
(Homogeneous medium means refractive index
independent of position)
• In general the path of the ray is determined by the Fermat’s principle.
(Similar to principle of least action in Mechanics)
“ The actual path between two points taken by a beam of light
is the one which takes the least time”
B
D
C
A
y
Light at the interface
The angles are defined with respect
to y-axis.
Incident
✓
✓
0
Reflected
n1
x
n2
z
✓=✓
0
Law of Reflection
Transmi/ed
sin ✓
n2
=
sin
n1
Snell’s law of refraction
Law of Reflection
A
B
h1
n1
n2
✓
✓
x
0
h2
l
x
C
l
Time taken by light to travel from A to B is
p
p
x2 + h21
(l x)2 + h22
t=
+
c
c
we can consider different such paths with x being the variable.
Law of Reflection
Fermat’s principle tells you that for the real path
dt
=0
dx
t=
c
p
x
x2 + h21
p
c (l
sin ✓1 = sin ✓2
p
l
x2 + h21
+
c
x
x)2 + h22
p
=0
(l
x)2 + h22
c
Snell’s Law
A
h1
h2
✓
x
l
x
C
B
l
t=
p
x2 + h21
+
c/n1
p
(l
x)2 + h22
c/n2
Snell’s Law
Fermat’s principle tells you that for the real path
dt
=0
dx
p
n1 x
x2 + h21
p
n2 (l
(l
x)
x)2 + h22
=0
If angles are small
n1 sin ✓ = n2 sin
✓
n2
=
n1
Optical Systems
•
Combination of mirrors, lenses and so on.
•
We need to trace the light through this optical elements!
•
Just need to use the Law of reflection and Snell’s law.
(sounds simple!!)
•
The principle of reversibility
(We can trace back)
•
The angle of deviation: 𝛼
✓
↵
Color dispersion
white light
✓
Glass
Red
Blue yellow
•
For typical materials the refractive index is larger for blue.
Color dispersion
•
Dispersive power
nB nR
V =
nY 1
•
Dispersive index
⌫ = 1/V
white light
✓
Glass
Red
Blue yellow
•
For typical materials the refractive index is larger for blue.
Examples for tracing light: Plane parallel plate
n1
n2
✓
✓
?????
Examples for tracing light: Plane parallel plate
n1
t
n2
✓
d
✓
✓
d = t sin ✓ 1
n1 cos ✓
n2 sin
◆
Home work
Examples for tracing light: Prism
↵
✓
monochromatic
light
Examples for tracing light: Prism
=✓+✓
↵
0
↵
✓0
0
✓
incident
0
sin ✓
n2
sin ✓
=
=
sin
n1
sin 0
transmitted
Angle of deviation
Examples for tracing light: Prism
1
sin
n2
2 (↵ +
=
n1
sin 12 ↵
↵
✓
✓0
0
incident
m
Angle of minimum
deviation
transmitted
Angle of deviation
m)
Convex and Concave spherical surfaces
A
F
C
Principal axis
centre of curvature
f
•
Primary focal point (F) is an axial point having the property
that any ray coming from it or proceeding toward it travels
parallel to the axis after refraction.
•
A plane perpendicular to the axis and passing through a focal
point is called a focal plane.
f is called the primary focal length.
•
Convex and Concave spherical surfaces
n1
A
n2
′
F
C
secondary focal point
f
0
secondary focal length
•
ʹ
Secondary focal point (F ) is an axial point having the property
that any incident ray travelling parallel to the axis will after
ʹ
refraction proceed toward or appears to come from F .
f 6= f
0
f0
n2
=
f
n1
Convex and Concave spherical surfaces
C
A
F
centre of curvature
f
Principal axis
Convex and Concave spherical surfaces
A
F C
f
0
Principal axis
Image formation: Reflection at a plane surface
👁
Q 🔦
•
Virtual image
Q’
the light appears to be coming from
Q’.
Refraction of light
•
Bending of light when it travels from one transparent medium to another.
•
Speed of light changes entering a denser medium.
Source: http://mserdelyiscience.weebly.com/uploads/1/3/8/6/13865601/phenomena_refraction.pdf
Refraction of light: Apparent Depth
Objects under the water looks nearer to the surface.
Source: http://mserdelyiscience.weebly.com/uploads/1/3/8/6/13865601/phenomena_refraction.pdf
Refraction of light: Mirage
Refraction of light: Mirage
Optical instruments: Human eye
Human visual system
Eyes +Path ways+ Part of the brain
•
Eyes behave like a camera. Capture lights and convert to neural
messages.
•
Pathways transmit and modify light from eyes to the brain.
•
Brain does the complex image processing.
Optical instruments: Human eye
Human visual system
Eyes +Path ways+ Part of the brain
•
The structure of the eye governs what we can see, and what we
cannot see! (infrared light is not visible to us, we need to modify
our vision)
Optical instruments: Human eye
Human visual system
Eyes +Path ways+ Part of the brain
•
•
The structure of eye varies from species to species.
For some worms, eyes mean a patch of photo sensitive pigment
on the surface of the skin, sense light which help them to
distinguish between day and night.
(may be the first version of the eyes)
Optical instruments: Human eye
View of a rabbit
:
View of a human
Source highered.mheducation.com/sites/dl/free/0070579431/19282/02_Sekular_36882.pdf
Optical instruments: Human eye
Light
Source:Wikipedia (Rhcastilhos)
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
Optical instruments: Human eye
Light
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
•
Cornea is transparent, and its transparency is very crucial for our
vision, especially the quality of our vision.
•
Cornea is extremely sensitive to foreign objects, has protective
measures like lid closing and tear production.
Optical instruments: Human eye
Light
•
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
Aqueous humor nourishes both the Cornea and lens.
Optical instruments: Human eye
Light
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
•
Iris has two layers, an outer layer with pigments and inner layer
with blood cells.
•
Iris means Rainbow in Greek, provides the color to your eyes,
depending how much it is pigmented.
Optical instruments: Human eye
Light
•
•
•
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
Lens, of all the body parts highest percentage of proteins.
We need to keep it transparent for a clear vision.
The opacity of the lens is called cataract, can be caused by the
exposure of ultra violet rays.
Optical instruments: Human eye
Light
•
•
•
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
Vitreous humor covers 2-3 rd of the volume of the eye.
This chamber is filled with transparent fluid called Vitreous.
You will also see floaters.
Optical instruments: Human eye
Light
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
•
Retina, a complex layered organization.
•
Light must pass through a complex network of neural elements
before reaching the photoreceptors which convert light energy
into neural signals.
Optical instruments: Human eye
Light
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
The neural signals generated by the photoreceptors pass through
a network of cells (bipolar and amacrine cells) that collect and
recombine the photoreceptor signals. These signals are passed
on to the retinal ganglion cells, where biologically important
information about the distribution of light over space and time is
extracted and recoded.
Optical instruments: Human eye
Light
•
•
•
•
•
•
Cornea
aqueous humor
Iris
Lens
Vitreous humor
Retina
The light interacts with the light-sensitive molecules called
photopigments in the photoreceptors. It triggers a cascade of
bio-chemical events, that generates photo signals with in the
photoreceptors. It triggers the neural activity in neurons of
retina.
Eye defects
Eye defects:corrections