Question 59 from the Professional Knowledge exam in the morning, 2014
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This post was last edited by xcx7319 on 2015-6-20 22:44. 59. For two flat thermal conductive walls with the same thickness but different materials, where the temperature drop Δt1 in the inner layer is smaller than the temperature drop Δt2 in the outer layer, which of the following statements regarding the relationship between the thermal conductivity of the two materials (λ1 for the inner layer, λ2 for the outer layer) and their thermal resistances (R1 for the inner layer, R2 for the outer layer) are incorrect? (A) λ1＞λ2, R1＞R2 (B) λ1＞λ2, R1＜R2 (C) λ1＜λ2, R1＜R2 (D) λ1＜λ2, R1＞R2. The online answers are ABD, but I think the correct choice is ACD
According to q=△t/R, since q1=q2 and △t1＜△t2, it follows that R1＜R2. Also, since R=b/(λA) and b1=b2 as well as A1=A2, it follows that λ1＞λ2. Therefore, R1＜R2 and λ1＞λ2. I agree with the original poster.
You can’t believe yourself!:lol