Lecture 10/24 Chapter 26 Geometrical Optics Flashcards
Reflection of Light
o A ray of light, the incident ray,
travels in a medium
o When it encounters a boundary
with a second medium, part of the
incident ray is reflected back into
the first medium
o This means it is directed backward
into the first medium
Specular reflection
o Specular reflection is reflection
from a smooth surface
o The reflected rays are parallel to
each other
o All reflection in this text is
assumed to be specular
Diffuse reflection
o Diffuse reflection is reflection
from a rough surface
o The reflected rays travel in a
variety of directions
Law of Reflection
o The normal is a line
perpendicular to the surface
o It is at the point where
the incident ray strikes
the surface
o The incident ray makes an
angle of θ1 with the normal
o The reflected ray makes an
angle of θ1
’ with the normal
o The angle of reflection is
equal to the angle of
incidence
θ1= θ1’
Refraction of Light
Light may refract into a material
where its speed is lower
o The angle of refraction is less
than the angle of incidence
o The ray bends toward the
normal
oLight may refract into a material where its
speed is higher
oThe angle of refraction is greater than the
angle of incidence
oThe ray bends away from the normal
Bending of light ray is called refraction.
Fiber Optics
o An application of internal
reflection
o Plastic or glass rods are
used to “pipe” light from
one place to another
o Applications include
o medical use of fiber
optic cables for
diagnosis and
correction of medical
problems
o Telecommunications
Quick Quiz
A container of flint glass (n = 1.66) holds a small
quantity of benzene (n = 1.501). What is the critical
angle for internal reflection of a ray in the glass
when it is incident on the glass-to-liquid surface?
a. 89.5º
b. 64.7º
c. 41.1º
d. 37.0º
b. 64.7º
Internal reflection reflects all of the light
Plane Mirror
& Notation
o Simplest possible mirror
o Properties of the image can be
determined by geometry
o One ray starts at P, follows path PQ
and reflects back on itself
o A second ray follows path PR and
reflects according to the Law of
Reflection
o The object distance is the distance from the object to the mirror or lens
o Denoted by p
o The image distance is the distance from the image to the mirror or lens
o Images are formed at the point where rays actually intersect or appear to originate
o Denoted by q
o The lateral magnification of the mirror or lens is the ratio of the image height to the object height
o Denoted by M
Plane Mirror
& Notation Equation
M=h’/h
A real image
o A real image is one in which light actually passes through the image point
o Real images can be displayed on screens
A virtual image
o A virtual image is one in which the light does not pass through the image point
o The light appears to diverge from that point
o Virtual images cannot be displayed on screens
Properties of the Image
Formed by a Plane Mirror
o The image is as far behind the mirror as the
object is in front
o q = p
o The image is unmagnified
o The image height is the same as the object height
o h’ = h and M = 1
o The image is virtual
o The image is upright
o It has the same orientation as the object
o There is an apparent left-right reversal in the
image
Quick-Quiz
1. You stand two feet away from a plane mirror. How far is it
from you to your image?
a. 2.0 ft
b. 3.0 ft
c. 4.0 ft
d. 5.0 ft
2. Which of the following best describes the image from a plane mirror?
a. virtual and magnification greater than one
b. real and magnification less than one
c. virtual and magnification equal to one
d. real and magnification equal to one
c. virtual and magnification equal to one
Spherical Mirrors:
Concave Mirror
o A concave spherical mirror has
the silvered surface of the mirror
on the inner, or concave, side of
the curve
o The mirror has a radius of
curvature of R
o Its center of curvature is the
point C
o Point V is the center of the
spherical segment
o A line drawn from C to V is called
the principal axis of the mirror
