Announcements

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• Announcements
• Office hours My office hours today 2 -3 pm
• or make an appointment
• Final exam Saturday 4/23, 3 5 pm,
• CUMULATIVE EXAM
• Make-up exam, Wednesday 4/20, 510 700 pm,
  NPB 1220, CUMULATIVE EXAM
• Always check out http//www.phys.ufl.edu/courses/
  phy2054/spring11/ for more announcements
• QUESTIONS? PLEASE ASK!

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Review

• Single slit diffraction
• In general, destructive interference occurs for a
  single slit of width for
• m ?1, ?2, ?3,
• Polarization
• Natural light is unpolarized
• Polarization occurs through selective absorption,
  reflection, scattering
• Polarization through absorption
• Transmission through crossed polarizers Maluss
  Law
• IT Io cos2 ?
• Polarization by reflection
• Brewsters angle
• n tan ?p

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Chapter 25
http//static-p4.fotolia.com/

• Optical Instruments

http//www.misericordia.mb.ca/Programs/ecAnatomy.h
tml
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Camera

• Converging lens
• Produces a real image
• Image is formed on an electric device
• CCD, CMOS
• Shutter exposure time
• Aperture light intensity
• Light intensity I D2/f2
• ƒ-number - ratio of lens focal length to diameter
• ƒ-number f/D
• ƒ-number ? lens speed
• A lens with a low f-number is a fast (and
  expensive) lens
• Camera lenses typcially range from 1.4 -11

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The Eye

• Amazing optical instrument!
• The normal eye focuses light and produces a sharp
  image
• Essential parts of the eye
• Cornea light passes through this transparent
  structure
• Aqueous Humor clear liquid behind the cornea

• The pupil
• A variable aperture
• The crystalline lens
• Most of the refraction takes place at the outer
  surface of the eye
• Iris (colored portion of the eye) muscular
  diaphragm that controls pupil size
• The f-number of the eye is from about 2.8 to 16

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The Eye Focusing

• Accommodation
• The eye focuses on an object by varying the shape
  of the crystalline lens through this process
• An important component is the ciliary muscle
  which is situated in a circle around the rim of
  the lens
• Thin filaments, called zonules, run from this
  muscle to the edge of the lens
• focusing on a distant object
• The ciliary muscle is relaxed
• The zonules tighten
• This causes the lens to flatten, increasing its
  focal length
• For an object at infinity, the focal length of
  the eye is equal to the fixed distance between
  lens and retina
• This is about 1.7 cm
• Focusing on near objects
• The ciliary muscles tense
• This relaxes the zonules
• The lens bulges a bit and the focal length
  decreases
• The image is focused on the retina

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The Eye Near and Far Points

• near point - closest distance for which the lens
  can accommodate to focus light on the retina
• Typically at age 10, this is about 18 cm
• Average is about 25 cm
• It increases with age, to 500 cm or more at age
  60
• far point - the largest distance for which the
  lens of the relaxed eye can focus light on the
  retina
• Normal vision has a far point of infinity

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Farsightedness

• Also called hyperopia
• The image focuses behind the retina
• Can usually see far away objects clearly, but not
  nearby objects

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Correcting Farsightedness

• A converging lens placed in front of the eye can
  correct the condition
• The lens refracts the incoming rays more toward
  the principle axis before entering the eye
• This allows the rays to converge and focus on the
  retina

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Nearsightedness

• Also called myopia
• In axial myopia the nearsightedness is caused by
  the lens being too far from the retina
• In refractive myopia, the lens-cornea system is
  too powerful for the normal length of the eye

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Correcting Nearsightedness

• A diverging lens can be used to correct the
  condition
• The lens refracts the rays away from the
  principle axis before they enter the eye
• This allows the rays to focus on the retina

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Problem 25.11 p 843

• The accommodation limits for Nearsighted Nicks
  eyes are 18 cm and 80 cm. When he wears his
  glasses, he can see far away objects clearly. At
  what minimum distance is he able to see objects
  clearly?

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Diopters

• Optometrists and ophthalmologists usually
  prescribe lenses measured in diopters
• The power of a lens in diopters equals the
  inverse of the focal length in meters
• P 1/f

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Simple Magnifier

• A simple magnifier consists of a single
  converging lens
• This device is used to increase the apparent size
  of an object
• The size of an image formed on the retina depends
  on the angle subtended by the eye

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The Size of a Magnified Image

• When an object is placed at the near point, the
  angle subtended is a maximum
• The near point is about 25 cm
• When the object is placed near the focal point of
  a converging lens, the lens forms a virtual,
  upright, and enlarged image

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Angular Magnification

• Angular magnification is defined as
• The angular magnification is at a maximum when
  the image formed by the lens is at the near point
  of the eye
• q - 25 cm
• Calculated by

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Problem 25.23 p 844

• A leaf of length h is positioned 71 cm in front
  of a converging lens with a focal length of 39
  cm. An observer views the image of the leaf at a
  position of 1.26 m behind the lens. (a) what is
  the magnitude of the lateral magnification (the
  ratio of the image size to the object size)
  produced by the lens? (b) What angular
  magnification is achieved by viewing the image of
  the leaf rather than viewing the leaf directly

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Answer to 25.11
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Answer to 25.23