Question 1

A nearsighted man wears contact lenses of -3.00 diopters. With these lenses, his corrected
near point is 25.0 cm. What is his uncorrected near point?

Accepted Answer

The answer of A nearsighted man wears contact lenses of...

Question 2

A person's hyperopic (farsighted) eye can focus on objects that are 75 cm away and
farther. What power and what focal length contact lenses should be prescribed so this
person can see objects 25 cm and farther from the eye?

Accepted Answer

The answer of A person's hyperopic (farsighted) eye can focus...

Question 3

A person's near point is 25 cm, and her eye lens is 2.7 cm away from the retina. What must be the focal length of this lens for an object at the near point of the eye to focus on the retina?
A) 2.4 cm
B) -2.4 cm
C) 2.6 cm
D) 3.4 cm
E) -3.4 cm

Accepted Answer

The lens formula is 1/f = 1/v - 1/u, where f is the focal length, v is the image distance (distance from the lens to the retina), and u is the object distance (distance from the lens to the object). For an object at the near point to be focused on the retina, u = -25 cm (negative because the object is in front of the lens), and v = 2.7 cm (positive because the image is formed on the retina behind the lens). Plugging these values into the lens formula gives 1/f = 1/2.7 - 1/(-25) = 1/2.7 + 1/25. Solving for f gives f ≈ 2.4 cm.

Question 4

What is the focal length of the corrective contact lens needed by a nearsighted person whose far point is at 60 cm?
A) -60 cm
B) -30 cm
C) +60 cm
D) +30 cm
E) +130 cm

Accepted Answer

The focal length of the corrective lens for a nearsighted person should allow them to see distant objects clearly. Since their far point is 60 cm, the lens needs to correct vision to infinity. The formula for lens power (P) is P = 1/f, where f is the focal length in meters. To correct to a far point of 60 cm (0.6 meters), the lens must have a focal length that brings parallel rays of light to focus at 60 cm. Thus, the focal length is -60 cm, indicating a diverging lens is needed. Negative because it corrects for nearsightedness by diverging light rays before they enter the eye.

Question 5

A farsighted girl has a near point at 2.0 m but has forgotten her glasses at home. The girl borrows eyeglasses that have a power of +2.75 diopters. With these eyeglasses, what is the near point of the
Girl, assuming that she wears them extremely close to her eyes?
A) 40 cm
B) 28 cm
C) 37 cm
D) 31 cm
E) 33 cm

Accepted Answer

The power of the eyeglasses is +2.75 diopters, which means they have a focal length of approximately 36.36 cm (1/2.75 m). Using the lens formula (1/f = 1/v - 1/u), where u is the original near point (200 cm), we can calculate the new near point (v) to be approximately 31 cm.

Question 6

As a treatment for cataracts (a cloudiness of the lens of the eye), the natural lens is removed and a plastic lens is implanted. After this is done a person can see distant objects clearly, but he cannot
Accommodate to focus on nearby objects. If such a person wanted to read a book at a distance of 25
Cm, he would have to wear contact lenses having a diopter power of
A) -1.78 diopters
B) +3.33 diopters
C) -4.00 diopters
D) +4.00 diopters
E) +2.78 diopters

Accepted Answer

The answer of As a treatment for cataracts (a cloudiness...

Question 7

For an eye that is 2.4 cm in diameter, what must be the range of focal lengths of the lens to
focus objects from the near point (25 cm) to infinity on the retina?

Accepted Answer

The answer of For an eye that is 2.4 cm...

Question 8

A machinist with normal vision has a near point at 25 cm. This machinist wears +4.25-diopter eyeglasses in order to do very close work. With these eyeglasses, what is the near point of the
Machinist? Assume that he wears the glasses extremely close to his eyes.
A) 15 cm
B) 7 cm
C) 17 cm
D) 10 cm
E) 12 cm

Accepted Answer

The answer of A machinist with normal vision has a...

Question 9

What is the power of a lens that has a focal length of -40 cm and a width of 2.0 cm?
A) +4.0 diopters
B) -2.5 diopters
C) -0.50 diopters
D) -50 diopters
E) +2.5 diopters

Accepted Answer

The power of a lens (P) is given by the formula P = 1/f, where f is the focal length in meters. Converting -40 cm to meters gives -0.40 m. Therefore, P = 1/(-0.40) = -2.5 diopters. The width of the lens is not relevant for calculating its power.

Question 10

A myopic (nearsighted) child wears contact lenses that allow her to have clear distant vision. The power of the lenses of her eyeglasses is -3.00 diopters. Without the corrective lenses, what is the far
Point of the girl?
A) 0.25 m
B) 0.42 m
C) 0.17 m
D) 0.50 m
E) 0.33 m

Accepted Answer

The answer of A myopic (nearsighted) child wears contact lenses...

Question 11

A person's eye lens is 2.8 cm from the retina, and his near point is at 25 cm. What must be the focal length of his eye lens so that an object at the far point of the eye will focus on the retina?
A) -2.8 cm
B) 2.8 cm
C) 2.2 cm
D) -2.4 cm
E) 2.4 cm

Accepted Answer

The focal length of the eye lens must be equal to the distance from the lens to the retina (2.8 cm) for an object at infinity (far point) to focus on the retina.

Question 12

A nearsighted person has a near point of 12 cm and a far point of 17 cm. If the corrective
lens is 2.0 cm from his eye, (a) what lens power will enable this person to see distant
objects clearly, and (b) what then will be the new near point of his eye?

Accepted Answer

The answer of A nearsighted person has a near point...

Question 13

The near point of a farsighted person is 65 cm. What power contact lens must he use to correct this problem and be able to read a book at a normal near point of 25 cm?
A) -2.4 diopters
B) +4.2 diopters
C) -4.2 diopters
D) +2.5 diopters
E) -2.5 diopters

Accepted Answer

To correct farsightedness, the lens must bring the near point from 65 cm to 25 cm. Using the lens formula (1/f = 1/v - 1/u) and converting to diopters (P = 1/f), we find the power needed is +2.5 diopters.

Question 14

A person uses corrective glasses of power -8.5 D that are worn 2.0 cm from her eye.
(a) Is she nearsighted or farsighted?
(b) What is her far point without glasses?

Accepted Answer

The answer of A person uses corrective glasses of power...

Question 15

A person is nearsighted with a far point of 75.0 cm.
(a) What focal length contact lens is needed to give him normal vision?
(b) What is the power of the corrective lens?

Accepted Answer

The answer of A person is nearsighted with a far...

Question 16

The power of a lens is 4.0 diopters and its diameter is 5.0 cm. What is the focal length of this lens?
A) 10 cm
B) 25 cm
C) 55 cm
D) 2.5 cm
E) 0.25 cm

Accepted Answer

The power of a lens in diopters is the inverse of the focal length in meters. Therefore, a lens with a power of 4.0 diopters has a focal length of 1/4.0 meters, which is 0.25 meters or 25 cm.

Question 17

What power (in diopters) of corrective contact lens is required to correct the vision of a
myopic eye whose far point is at 170 cm?

Accepted Answer

The answer of What power (in diopters) of corrective contact...

Question 18

A nearsighted person has a far point of 50 cm for his right eye and 150 cm for his left eye.
For each eye, what power contact lens will allow the person to see gorgeous sunsets?

Accepted Answer

The answer of A nearsighted person has a far point...

Question 19

A farsighted boy has a near point at 2.3 m and requires contact lenses to correct his vision to the normal near point. What is the correct choice of lens power for the contact lenses?
A) +3.6 diopters
B) +0.28 diopters
C) -0.28 diopters
D) +1.8 diopters
E) -3.6 diopters

Accepted Answer

The lens power needed is calculated using the formula for lens power: P = 1/f, where f is the focal length in meters. The boy's near point is 2.3 m, and the normal near point is 0.25 m. The lens should bring the near point from 2.3 m to 0.25 m. The lens power required is P = 1/0.25 - 1/2.3 = 4 - 0.4348 = 3.5652 diopters, which rounds to +3.6 diopters.

Question 20

What is the power of the lens that has a focal length of 40 cm and a diameter if 5.0 cm?
A) +2.7 diopters
B) -2.5 diopters
C) +0.20 diopters
D) +2.5 diopters
E) +20 diopters

Accepted Answer

The power of a lens (P) is given by the formula P = 1/f, where f is the focal length in meters. Converting 40 cm to meters gives 0.4 m. Therefore, P = 1/0.4 = 2.5 diopters. The positive sign indicates a converging lens.

Quiz 25: Optical Instruments

A nearsighted man wears contact lenses of -3.00 diopters. With these lenses, his corrected near point is 25.0 cm. What is his uncorrected near point?

A person's hyperopic (farsighted) eye can focus on objects that are 75 cm away and farther. What power and what focal length contact lenses should be prescribed so this person can see objects 25 cm and farther from the eye?

A person's near point is 25 cm, and her eye lens is 2.7 cm away from the retina. What must be the focal length of this lens for an object at the near point of the eye to focus on the retina?

What is the focal length of the corrective contact lens needed by a nearsighted person whose far point is at 60 cm?

A farsighted girl has a near point at 2.0 m but has forgotten her glasses at home. The girl borrows eyeglasses that have a power of +2.75 diopters. With these eyeglasses, what is the near point of the Girl, assuming that she wears them extremely close to her eyes?

For an eye that is 2.4 cm in diameter, what must be the range of focal lengths of the lens to focus objects from the near point (25 cm) to infinity on the retina?

A machinist with normal vision has a near point at 25 cm. This machinist wears +4.25-diopter eyeglasses in order to do very close work. With these eyeglasses, what is the near point of the Machinist? Assume that he wears the glasses extremely close to his eyes.

What is the power of a lens that has a focal length of -40 cm and a width of 2.0 cm?

A myopic (nearsighted) child wears contact lenses that allow her to have clear distant vision. The power of the lenses of her eyeglasses is -3.00 diopters. Without the corrective lenses, what is the far Point of the girl?

A person's eye lens is 2.8 cm from the retina, and his near point is at 25 cm. What must be the focal length of his eye lens so that an object at the far point of the eye will focus on the retina?

A nearsighted person has a near point of 12 cm and a far point of 17 cm. If the corrective lens is 2.0 cm from his eye, (a) what lens power will enable this person to see distant objects clearly, and (b) what then will be the new near point of his eye?

The near point of a farsighted person is 65 cm. What power contact lens must he use to correct this problem and be able to read a book at a normal near point of 25 cm?

A person uses corrective glasses of power -8.5 D that are worn 2.0 cm from her eye. (a) Is she nearsighted or farsighted? (b) What is her far point without glasses?

A person is nearsighted with a far point of 75.0 cm. (a) What focal length contact lens is needed to give him normal vision? (b) What is the power of the corrective lens?

The power of a lens is 4.0 diopters and its diameter is 5.0 cm. What is the focal length of this lens?

What power (in diopters) of corrective contact lens is required to correct the vision of a myopic eye whose far point is at 170 cm?

A nearsighted person has a far point of 50 cm for his right eye and 150 cm for his left eye. For each eye, what power contact lens will allow the person to see gorgeous sunsets?

A farsighted boy has a near point at 2.3 m and requires contact lenses to correct his vision to the normal near point. What is the correct choice of lens power for the contact lenses?

What is the power of the lens that has a focal length of 40 cm and a diameter if 5.0 cm?