Question

In question number 3, the thermal conductivity (in `W m^(-1) K^(-1)`) if air is
A. `1/10`
B. `1/12`
C. `1/14`
D. `9/130`

Answer 1

Correct Answer - C
The temperature difference across the plate.
`DeltaT_("plate") = ((dQ)/dt)xx (l_("plate"))/(K_("plate") xx A) = (65 xx 4 xx 10^(-3))/(1 xx 1.3) = 0.2 K`
`:. DeltaT_("air") = 13 - 2DeltaT_("plate") = 12.6 K`
`K_("air") = (((dQ)/(dt))xxl_("air"))/(ADeltaT_("air")) = (65 xx 18 xx 10^(-3))/(1.3 xx 12.6) = 1/14 W m^(-1) K^(-1)`