Physics quiz question: simple magnifier

Physics 205B Quiz 2, fall semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 24.29

A Physics 205B student would like to use a +10.0 D converging lens as a simple magnifier. What is the angular magnification of this lens as used by a relaxed eye?
(A) +0.40.
(B) +2.5.
(C) +10.
(D) +40.

Correct answer (highlight to unhide): (C)

The focal length of the lens (in m) is the inverse of the refractive power P (in diopters, D, or equivalently m^–1):

f = 1/P.

The angular magnification of a converging lens, used as a simple magnifier (and a relaxed eye) is given by:

M = N/f,

where N is the nominal near point of 0.25 m. Thus the angular magnification is:

M = N/f = N·P = (0.25 m)·(+10.0 m^–1) = +2.5.

(Response (A) is 1/(N·P); response (C) is P; and response (D) is P/N.)

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

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