Physics quiz question: contact lens for myopia

Physics 205B Quiz 2, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 24.4, Practice Problem 24.4

A Physics 205B student with an uncorrected far point of 3.5 m uses contact lenses. When a contact lens is used by this student to look very far away, the object for the eye is an intermediate virtual image produced by the contact lens. This intermediate virtual image is located:
(A) at ∞.
(B) 0.25 m from the eye.
(C) at the uncorrected far point of the eye.
(D) at the uncorrected near point of the eye.

Correct answer: (C)

The contact lens must produce a virtual (erect) image at a distance that the eye can see. Thus for a contact lens that fully corrects for myopia (nearsightedness), for objects at p_contacts = +∞, the contact lens must create a virtual image at a distance of q_contacts = –3.5 m, which is at the uncorrected far point of the eye.

Student responses
Section 70856
(A) : 0 students
(B) : 1 student
(C) : 9 students
(D) : 1 student

Success level: 82%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.40