The Refraction of Light: Lenses and Optical Instruments

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Chapter 26

• The Refraction of Light Lenses and Optical
  Instruments

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The Index of Refraction
Definition of the Index of Refraction The index
of refraction n of a material is the ratio of
the speed of light in a vacuum to the speed v in
the material
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Snells Law
Snells Law of Refraction When light travels
from a material with refractive index n1 into a
material with a refractive index n2 , the
refractive ray, the incident ray, and the normal
to the interface between the materials all lie in
the same plane. The angle of refraction ?2 is
related to the angle of incidence ?1 by

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Apparent Depth
Example
A search light on a yacht is being used at night
to illuminate a sunken chest. At what angle of
incidence ?1 should the light be aimed? (p. 786)
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Apparent Depth
Apparent Depth of observer directly above the
object
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Total Internal Reflection

• When the angle of incidence reaches a critical
  value ?c, the angle of refraction is 90o the
  refracted ray points along the surface.
• Total Internal Reflection
• When the angle of incidence exceeds the critical
  angle, there is no refracted light all the
  incident light is reflected back into the medium
  from which it came.

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Total Internal Reflection
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Example
A beam of light propagating through a diamond
air interface at an angle of incidence is 28o.
Will part of the beam enter the air (n2 1.00)
or will the beam be totally reflected at the
interface? (p. 791)
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Fiber Optics

• endoscopy bronchoscope colonoscope

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The Dispersion of Light Prisms
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The Dispersion of LightRainbows
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Lenses
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The Formation of Images by Lenses
Ray 1. This ray is initially parallel to the
principal axis and, therefore, passes through
the focal point F after it is refracted. Ray
2. This ray passes through the focal point F and
is refracted parallel to the principal axis.
Ray 3. This ray travels directly through the
center of the thin lens without any bending
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The Formation of Images by Lenses
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The Formation of Images by Lenses
Ray 1. This ray is initially parallel to the
principal axis and, therefore, passes through
the focal point F after it is refracted. Ray
2. This ray passes through the focal point F and
is refracted parallel to the principal axis.
Ray 3. This ray travels directly through the
center of the thin lens without any bending
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The Formation of Images by Lenses
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The Thin Lens and Magnification Equation
Thin Lens Equation
The Magnification Equation
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Sign Conventions for Spherical Mirrors
Focal Length
f is ____ for a converging lens. f is ____for a
diverging lens.
Object Distance
d0 is ____ if the object is to the left of a lens
(real object). d0 is ____if the object is to the
right of the lens (virtual object).
Image Distance
di is _____ if the object is in right of a lens
(real image). di is _____ if the object is left
of a lens (virtual image).
Magnification
m is ____for an image that is upright with
respect to the object. m is ____for an object
that is inverted with respect to the object.
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The Thin Lens and Magnification Equation
Example
A 1.70-m-tall person is standing 2.50 m in front
of a camera. The camera uses a converging lens
whose focal length is 0.0500 m. (a) Find the
image distance and determine whether the image is
real or virtual. (b) Find the magnification and
height of the image on the film. (p. 802)
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Lenses in Combination
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Lenses in Combination
Example
The objective and eyepiece of the compound
microscope are both converging lenses and have
focal lengths of f0 15.0 mm and fe 25.5 mm. A
distance of 61.0 mm separates the lenses. The
miscroscope is being used to examine an object
placed d01 24.1 mm in front of the objective.
Find the image distance (p. 805)
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The Human Eye
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The Human Eye
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Optics of the Eye
___________ The point nearest the eye at
which an object can be placed and still produce a
sharp image on the retina
__________ The location of the farthest
object on which the fully relaxed eye can focus
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Nearsightedness
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Farisightedness
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Refractive Power
Refractive Power of a lens (in diopters)
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Lens Aberrations