PHYS 202: Chapter 23
50 Cards in this Set
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A normal eye is able to focus on both distant and close objects through a
process called accommodation. Its accomplished by __________
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changing the shape of the lens
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The location of the image is a function of _________
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the object distance
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How to focus the image?
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By changing the distance between the
lens and the film
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Cameras also have an iris to _________
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control the amount of light entering
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Lights strikes the cornea where
____________
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the light is first refracted
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The Iris controls __________
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the amount of
light that enters
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The lens ___________
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further refracts the light
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The image is formed on _________
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the
Retina
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The optic nerve ___________
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reads out the
retina
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Coming from air, most of the
refraction occurs at ____________
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the cornea
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Unlike a camera, the eye can not adjust the distance between the lens and
the retina
But it can ________________
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adjust the lens (change the focal length)
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Distant object: The lens is less curved by
________________
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relaxing the ciliary muscle
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Refraction at the cornea, but the lens
can _______________
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fine tune the refraction
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Close object: The lens is ______________
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more curved
by contracting the ciliary muscle
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A normal eye should be able to accommodate objects as close as _______
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25 cm
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Hyperopia =
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(farsighted)
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How to restore normal vision
to a farsighted person
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Form an image of the object at the near point using a corrective lens
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to restore normal vision to someone with myopia
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Form an image of the object at the far point using a corrective lens
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Corrective lenses are prescribed to ________________
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form an image of an object at a location
where the eye can easily focus upon
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The sign of the focal length determines __________
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the type of lens
converging or diverging
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The strength of the corrective lens is usually measured in the unit _______
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diopter
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converging lenses form _______ virtual images
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enlarged
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diverging lenses form _______ virtual images
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shortened
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apparent size
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angular size
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If you want to see something bigger, _________
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get closer for a larger
apparent size (angular size) up to the near point.
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A farsighted person has a near point of 50 cm (rather than the normal
25 cm).
i ) What is the focal length of the required corrective lens?
ii ) What is the strength of the prescribed corrective lens
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+50 cm
+2.0 diopter
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A nearsighted person has a far point of 300 cm.
i) What is the focal length of the required corrective lens?
ii ) What is the strength of the prescribed corrective lens
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-300 cm
-0.33 diopter
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An eye doctor prescribes glasses with a converging lens having a strength
of + 4.0 diopter.
i) E2. Is the patient nearsighted or farsighted
ii) What is the location of their near point
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farsighted
near point of 103 cm
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Magnifying Glass
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Increase the apparent size of an image without forcing us to focus on
something too close
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The angular magnification measures _________
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the
improvement of using a magnifying glass
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Which type of lens gives us a real image?
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Converging lens with the object outside the focal point
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A microscope uses two lenses to form an greatly enlarged image
The objective lens forms __________
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an enlarged, real image of the object
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microscope and telescope: The final virtual image is
_________________
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very large (the goal)
and distant (comfortable)
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telescope uses
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an objective lens to form a closer, enlarged, real image of the object
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need an eyepiece with ________
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the real image as an object
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Galilean Telescope
____________
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Replace the eyepiece with a diverging lens
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galilean telescope: the final virtual image is ______
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upright
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A 0.7-cm long insect is viewed through a 8X magnifying glass.
i) Approximately what angle does it appear to subtend the eye
ii)What angle does it appear to subtend if the insect is viewed unaided at the
closest comfortable location
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13deg
1.6deg
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A forensic scientist is using a standard biological microscope with a 15X
objective and a 5X eyepiece to examine a hair from a crime scene.
i) What is the focal length of the objective lens?
ii) What is the focal length of the eyepiece?
iii) How far from the objective is the hair?
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= 1.07 cm
= 5 cm
= 1.14 cm
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The distance between the objective and eyepiece lenses of an inverting
telescope with a 5X eyepiece is 55 cm.
i) What is the telescopes overall magnification?
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10x
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A farsighted eye has a near point of 140 cm. Objects closer than 140 cm are not seen clearly. A converging lens is used to permit clear vision of a book placed 25 cm in front of the eye. Find the focal length of the lens and express its strength in diopters. (Do not enter a unit)
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3.29
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A magnifying glass enlarges an object by an angular factor of 3. What is its approximate focal length? ( cm)
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8.33 cm
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A magnifying lens focuses the sun's rays to a point 11 cm away from the lens. What power magnifying glass will this lens make? (no unit)
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2.27
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An eyepiece of 2.2- cm focal length and an objective of 0.29- cm focal length are used in a standard microscope.
What power should be marked on the eyepiece? (no unit)
What power should be marked on the objective? (no unit)
What is the overall magnification of the combination?
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1.14×101
5.52×101
6.27×102
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An astronomical telescope is designed with an overall magnification of 60x. The objective has a focal length of 86.0 cm.
What should be the focal length of the eyepiece?
How far should the eyepiece be from the objective?
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1.43 cm
8.74×101 cm
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A Galilean telescope with two lenses spaced 30 cm apart has an objective of 50- cm focal length.
What is the focal length of the eyepiece?
What is the magnification of the telescope? Assume the object to be very far away. (No unit)
What must be the separation between the two lens…
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-2.00×101 cm
2.50
3.13×101 cm
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A nearsighted person has a far point of one meter. Objects beyond one meter are not sharply focused. What lens should me used to obtain clear vision for objects at infinity? (in diopters)
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-1.00
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a farsighted person wears eyeglasses with a lens strength of +1.5 diopters. What is the near point for that person's eyes?
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4 m
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a dime (diameter 1.8 cm) is viewed through a 5x magnifying glass. Approx what angle does it appear to subtend at the eye?
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20.6 deg
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in a lab microscope, the first image of a specimen is formed inside the microscope 15 cm from the objective lens. if the specimen is 3.0 mm from the objective when the image is in focus, what is the focal length of the objective?
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2.9 mm
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PHYS 202: Exam 1