Physics clicker question: opening in heated metal plate

Physics 5A, Fall Semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Conceptual Question 13.4 (extended)

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the beginning of their learning cycle:

[0.6 participation points.] A square opening is made in a metal plate. If the metal plate is heated up from room temperature by 100 degrees C, what happens to the size of the square opening?
(A) The square opening becomes smaller.
(B) The square opening becomes larger.
(C) The square opening remains the same size as before.
(D) (Not enough information is given.)
(E) (I'm lost, and don't know how to answer this.)

Sections 0906, 0907
(A) : 19 students
(B) : 12 students
(C) : 2 students
(D) : 0 students
(E) : 0 students

Correct answer: (B)

All dimensions, external as well as internal in the metal plate expand when it is heated, and this includes the dimensions of the square opening. However, the hole in the middle of a ring of donut batter will get smaller as the donut cooks in oil, but this is an entirely different phenonomenon--no "fluffy donuts!"