Physics quiz question: doubling sleeping pad thickness

Physics 205A Quiz 7, fall semester 2019
Cuesta College, San Luis Obispo, CA

Rebecca J. Crawford

A Klymit® Static V sleeping pad[*] (area of 1.07 m2 and thickness of 0.0635 m) has a thermal resistance of 0.21 K/watts. If the pad were made twice as thick, its __________ would increase.
(A) thermal resistance.
(B) thermal conductivity.
(C) (Both of the above choices.)
(D) (Neither of the above choices.)

[*] klymit.com/static-v-camping-sleeping-pad.html.

Correct answer (highlight to unhide): (A)

The thermal resistance R of an object can be related to the thermal conductivity κ of its material:

R = d/(κ·A),

where d is the thickness of the object that heat must conduct through, and A is the cross-sectional area. As the thermal conductivity κ is an intensive property of the material, it would not change because of doubling the thickness of the pad, in contrast to the thermal resistance, which would increase as a result.

Sections 70854, 70855
Exam code: quiz07VlnC
(A) : 36 students
(B) : 6 students
(C) : 9 students
(D) : 0 students

Success level: 71%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.58

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