(a) What is the power of the eye when viewing an object 50.0 cm away?
(b) What is the power of the eye when viewing an object 3.00 m away. Take the lens-to-retina distance to be 2.00 cm.
Answer: (a) 52 D (b) 50.3 D (Click and drag over the answer to highlight it)
9.2
Suppose a certain person’s visual acuity is such that he can see objects clearly that form an image 4.00 μm high on his retina. What is the maximum distance at which he can read the 75.0 cm high letters on the side of an airplane? Assume the lens-to-retina distance is 2.00 cm.
Answer: 3.75 km
9.3
A laser vision correction reshaping the cornea of a myopic patient reduces the power of his eye by 9.00 D, with a ±5.0% uncertainty in the final correction.
(a) What is the range of diopters for spectacle lenses that this person might need after LASIK procedure?
(b) Was the person nearsighted or farsighted before the procedure? How do you know?
Answer: +/- 0.45 D which gives a range of 0.9 D
9.4
A student’s eyes, while reading the blackboard, have a power of 51.0 D. How far is the board from his eyes? Assume the lens-to-retina distance is 2.00 cm.
Answer: 98 cm
9.5
A very myopic man has a far point of 20.0 cm.
(a) What power contact lens (when on the eye) will correct his distant vision?
(b) Repeat this for eyeglasses held 1.50 cm from the eyes.
Answer: (a) -5 D (b) -5.4 D
9.6
A mother sees that her child’s contact lens prescription is 0.750 D.
(a) What is the child’s near point?
(b) Repeat for glasses that are 2.20 cm from the child’s eyes.
Answer: (a) 30.8 cm (b) 29.7 cm
9.7
A boy has a near point of 50 cm and a far point of 500 cm. Will a –4.00 D lens correct his far point to infinity? Explain why or why not.
Answer: Yes
9.8
(a) What magnification is produced by a 0.150 cm focal length microscope objective that is 0.155 cm from the object being viewed?
(b) What is the overall magnification if an 8× eyepiece (one that produces a magnification of 8.00) is used?
Answer: (a) 30X (b) 240X
9.9
(a) Where does an object need to be placed relative to a microscope for its 0.500 cm focal length objective to produce a magnification of –400?
(b) Where should the 5.00 cm focal length eyepiece be placed to produce a further fourfold (4.00) magnification?
Answer: (a) 0.501 cm (b) The eyepiece should be 204 cm behind the objective lens.
9.10
An amoeba is 0.305 cm away from the 0.300 cm focal length objective lens of a microscope.
(a) Where is the image formed by the objective lens?
(b) What is this image’s magnification?
(c) An eyepiece with a 2.00 cm focal length is placed 20.0 cm from the objective. Where is the final image?
(d) What magnification is produced by the eyepiece?
(e) What is the overall magnification?
Answer: (a) 18.3 cm behind the objective (b) -60 (c) -11.3 cm (in front of the eyepiece) (d) +6.67 (e) -400
Physics Education Research at UNG 