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Question :
41) A person's eye lens 2.7 cm away from the

41) A person's eye lens is 2.7 cm away from the retina. This lens has a near point of 25 cm and a far point at infinity.

(a) What must the focal length of this lens be in order for an object placed at the near point of the eye to focus on the retina?

(b) What must the focal length of this lens be in order for an object placed at the far point of the eye to focus on the retina?

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

A) -60 cm

B) -30 cm

C) +30 cm

D) +60 cm

E) +130 cm

43) A nearsighted person has her distant vision corrected using a -2.0-diopter contact lens. Her uncorrected near point is 15 cm. What is her near point using this lens if the lens is 2.0 cm from the eye?

A) 17 cm

B) 20 cm

C) 13 cm

D) 18 cm

E) 15 cm

44) The near point of a person's uncorrected eyes is 125.0 cm and the far point is at infinity. What is the focal length of a contact lens that will move the near point to 25.0 cm from this person's eyes?

A) -100 cm

B) -31.3 cm

C) 10.2 cm

D) 20.8 cm

E) 31.3 cm

45) The near point of a farsighted person's uncorrected eyes is 80 cm. What power contact lens should be used to move the near point to 25 cm from this person's eyes?

A) 2.8 diopters

B) -2.8 diopters

C) -4.0 diopters

D) -4.2 diopters

E) 4.2 diopters

46) What power contact lens must be used to correct the vision of a nearsighted person whose far point is 40 cm?

A) 2.5 diopters

B) -2.5 diopters

C) -3.6 diopters

D) -4.0 diopters

E) 4.0 diopters

47) What is the uncorrected near point of a person who has a near point that is 25 cm from his eyes when he is wearing 3.33-diopter contact lenses?

A) 1.5 m

B) 0.50 m

C) 1.9 m

D) 0.75 m

E) 0.60 m

48) A person can read the newspaper when it is held at 60 cm from his eyes. What should the focal length of his contact lenses be to allow him to read the newspaper comfortably at a distance of 30 cm?

A) -30 cm

B) 30 cm

C) -60 cm

D) 60 cm

E) 90 cm

49) A man is nearsighted and cannot see things clearly beyond 110from his eyes. What is the focal length of the contact lenses that will enable him to see very distant objects clearly?

A) 50 cm

B) -50 cm

C) -110 cm

D) 110 cm

E) -30 cm

50) A nearsighted physicist cannot see things clearly beyond 90 cm from her eyes. What is the power of the contact lenses that will enable her to see very distant objects clearly?

A) 1.1 diopters

B) -1.1 diopters

C) -1.7 diopters

D) -2.2 diopters

E) 2.2 diopters