Physics quiz question: glass sheet versus sheet plastic contraction

Physics 205A Quiz 7, spring semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 13.10

A glass sheet and a plastic sheet both have the same dimensions at an initial temperature of 15° C. When both sheets are cooled down to the same final temperature, the glass sheet is slightly smaller than the plastic sheet. The __________ sheet has the greater coefficient of linear expansion.
(A) glass.
(B) plastic.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

The relation between temperature change and the fractional change in length of an object is given by:

α·∆T = ∆L/L,

where L is the original length (or width) of the object, and α is the material-specific linear expansion coefficient. The glass sheet and the plastic sheet have the same ∆T decrease in temperature and the same original L length and width dimensions; thus a greater ∆L (as for the glass sheet) must correspond to a greater expansion coefficient α for the glass sheet.

Student responses
Sections 30880, 30881
(A) : 21 students
(B) : 18 students
(C) : 0 students
(D) : 0 students

Success level: 53%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55