Optics
The Study of Light
Areas of Optics
Geometric Optics
 Light as a ray.
 Physical Optics
 Light as a wave.
 Quantum Optics
 Light as a particle.

Optical images
•
Nature
•
•
•
Orientation
•
•
•
real (converging rays)
virtual (diverging rays)
upright
inverted
Size
•
•
•
true
enlarged
reduced
Law of Reflection
•
Angle of incidence equals
angle of reflection.
r
i
Plane Mirror
+
object
5 cm
-
Image
-5 cm
Spherical mirrors
+
(where reflected rays go)
(dark side)
concave
shiny
Focal length, f, is positive
+
(where reflected rays go)
(dark side)
convex
shiny
Focal length, f, is negative
Parts of a
Spherical Concave Mirror
+
-
Vertex
Center
Focus
Principle axis
Spherical Concave Mirror
(object outside center)
c
p
C
f
F
Real,
Inverted,
Reduced
Image
Spherical Concave Mirror
(object at center)
C
F
Real,
Inverted,
True
Image
Spherical Concave Mirror
(object between center and focus)
C
F
Real,
Inverted,
EnlargedI
mage
Spherical Concave Mirror
(object at focus)
C
F
No image
Spherical Concave Mirror
(object inside focus)
C
F
Virtual,
Upright,
Enlarged
Image
Parts of a
Spherical Convex Mirror
+
Principle axis
Focus
Center
Spherical Convex Mirror
F
Virtual,
Upright,
Reduced
Image
C
Mirror equation #1
• 1/si + 1/so = 1/f
si: image distance
• so: object distance
• f: focal length
•
Mirror equation # 2
•
M = -si/so = hi/ho
si: image distance
• so: object distance
• hi: image height
• ho: object height
• M: magnification
•
Concave vs convex mirrors

Concave



Image is real when
object is outside
focus
Image is virtual
when object is
inside focus
Focal length f is
positive

Convex


Image is always
virtual
Focal length f is
negative
Real vs Virtual images

Real


Formed by
converging light
rays
si is positive when
calculated with
mirror equation

Virtual


Formed by
diverging light
rays
si is negative when
calculated with
mirror equation
Upright vs Inverted images

Upright


Always virtual if
formed by one
mirror or lens
hi is positive when
calculated with
mirror/lens
equation

Inverted


Always real if
formed by one
mirror or lens
hi is negative when
calculated with
mirror/lens
equation
Definition: Refraction
Change in speed of light as it
moves from one medium to
another.
Can cause bending of the light
at the interface between
media.
Index of Refraction
n=
speed of light in vacuum
speed of light in medium
n = c/v
Snell’s Law
angle of incidence
1
n1sin 1 = n2sin 2
n1
2
angle of refraction
n2
n1 < n2
light bends toward normal
1
n1
2
n2
n1 > n2
1
light bends away from
normal
n1
2
n2
Dispersion
The separation of white light
into colors due to different
refractive indices for
different wavelengths.
Dispersion
Due to different indices of
refraction for different
wavelengths of light.
Critical Angle of
Incidence
c
Light would refract
90o so it reflects
instead, undergoing
total internal
reflection.
n1
r
n2
n1 > n2
Calculating Critical Angle
n1sin(1) = n2sin(2)
o
n1sin(90 ) = n2sin(2)
n1 = n2sin(c)
Total Internal Reflection
i
r
Occurs only when
angle of incidence >
critical angle
n1
n2
Announcements
3/23/2016
Turn in homework (lens
problems) on overhead.
 Lab report will be due next
week (on looseleaf or graph
paper).

Consider a lens with f = 20 cm.
You place a 5 cm tall object 30 cm in
front of the lens.
a)Draw the ray diagram and construct
the image.
b)Calculate the image distance and
height using the lens/mirror
equations.
c) Name the image.
Converging lens #1
2F
Real,
Inverted,
Reduced
Image
F
+
C
F
2F
Converging lens #2
2F
Real,
Inverted,
True
Image
F
+
C
F
2F
Converging lens #3
2F
Real,
Inverted,
Enlarged
Image
F
+
C
F
Converging lens #4
F
Virtual,
Upright,
Enlarged
Image
+
C
F
For converging lenses
•
•
•
•
•
f is positive
so is positive
si is positive for real images and
negative for virtual images
M is negative for real images and
positive for virtual images
hi is negative for real images and
positive for virtual images
Diverging lens
F
Virtual,
Upright,
Reduced
Image
+
C
F
For diverging lenses
f is negative
• so is positive
• si is negative
• M is positive and < 1
• hi is positive and < ho
•