Physics quiz question: microscope eyepiece used as simple magnifier

Physics 205B Quiz 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

A Leitz Ortholux microscope[*] (–47× magnification) has an eyepiece lens with a focal length of +1.8 cm, and a 17.0 cm distance between the objective and eyepiece. If the +1.8 cm focal length eyepiece lens was instead used by itself as a simple magnifier, its angular magnification would be:
(A) +1.9×.
(B) +14×.
(C) +23×.
(D) +45×.

[*] microscopy-uk.org.uk/mag/artnov15/The%20Mechanical%20Tube%20Length%20Version%201.pdf.

Correct answer (highlight to unhide): (B)

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 25 cm. Thus the angular magnification is:

M = N/f = (0.25 m)/(+1.8 cm) = +13.888888889×,

or to two significant figures, +14×.

(Response (A) is solving for d_i if the (real) image created by this converging lens is at d_o = +25 cm; response (C) is N – f_eyepiece; and response (D) is N·f_eyepiece.)

Sections 30882, 30883
Exam code: quiz02J4sZ
(A) : 3 students
(B) : 17 students
(C) : 7 students
(D) : 3 students

Success level: 57%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73