20190826

Physics quiz question: computer chip nanoacreage

Physics 205A Quiz 1, fall semester 2019
Cuesta College, San Luis Obispo, CA

A "nanoacre" is defined to be the area of a square 0.0792 inches by 0.0792 inches.[*] A VLSI (Very Large Scale Integration) computer chip has an area of 520 mm2.[**] A meter is defined to be 1,000 mm, and an inch is exactly equal to 25.4 mm. This computer chip has an area of:
(A) 4.05 nanoacres.
(B) 1.3×102 nanoacres.
(C) 2.6×102 nanoacres.
(D) 2.1×103 nanoacres.

[*] wki.pe/List_of_humorous_units_of_measurement#Nanoacre.
[**] johnloomis.org/ece531/notes/intro/intro.html.

Correct answer (highlight to unhide): (B)

The area of the computer chip in nanoacres can be determined from converting the units from the given value of square inches, by setting up conversion factors such that unwanted units cancel (in2, mm2) while desired units remain (nanoacres):

520 mm2 = 520 mm2·((1 in)/(25.4 mm))·((1 in)/(25.4 mm))·((1 nanoacre)/((0.0792 in)·(0.0792 in))),

520 mm2 = 520 mm2·((1 in)/(25.4 mm))·((1 in)/(25.4 mm))·((1 nanoacre)/((0.0792 in)·(0.0792 in))),

520 mm2 = 128.4947983629 nanoacres,

or to two significant figures, the computer chip area is 1.3×102 nanoacres.

(Response (A) is ((0.0792)·(25.4))2; response (C) is (520)/((0.0792)·(25.4)); response (D) is (520)·((0.0792)·(25.4))2).)

Sections 70854, 70855
Exam code: quiz01B34t
(A) : 4 students
(B) : 35 students
(C) : 8 students
(D) : 8 students

Success level: 64%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.58

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