## 20161210

### Physics quiz question: thermal paste heat conduction

Physics 205A Quiz 7, fall semester 2016
Cuesta College, San Luis Obispo, CA

"thermal paste"
flic.kr/p/4Qx9Vz

The rate of heat conducted per time from a hot Intel® "Skylake"-H Core i7 computer chip, through a thin layer of thermal paste to a cooling unit is 45 watts[*]. Increasing just the thickness of the thermal paste layer would ___________ the rate of heat conducted per time through it.
(A) decrease.
(B) not change.
(C) increase.
(D) (Not enough information is given.)

[*] wki.pe/Skylake_(microarchitecture).

Correct answer (highlight to unhide): (A)

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

R = d/(κ·A),

where d is the thickness of the object that heat must conduct through, and A is the cross-sectional area. Increasing the thickness d of the thermal paste layer would then increase the thermal resistance R of this layer. The rate of heat per time conducted is given by:

Power = ∆T/R,

where the temperature difference ∆T is measured between the hotter chip and the cooler calling unit above it, and since increasing the thickness d of the thermal paste layer would increase the thermal resistance R of this layer, the rate of heat conducted through the layer would then decrease.

Sections 70854, 70855, 73320
Exam code: quiz07p4sT
(A) : 45 student
(B) : 1 student
(C) : 6 students
(D) : 0 students

Success level: 87%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.29