Question

Two identical metal wires of thermal conductivities $K _{1}$ and $K _{2}$ respectively are connected in series. The effective thermal conductivity of the combination is:

• A. $\frac{2 K _{1} K _{2}}{ K _{1}+ K _{2}}$
• B. $\frac{ K _{1}+ K _{2}}{2 K _{1} K _{2}}$
• C. $\frac{ K _{1}+ K _{2}}{ K _{1} K _{2}}$
• D. $\frac{ K _{1} K _{2}}{ K _{1}+ K _{2}}$

Answer 1

Answer: (A)

$R _{\text {eff }}=\frac{l}{ K _{1} A }+\frac{l}{ K _{2} A }=\frac{2 l}{ K _{ eg } A }$
$K _{ eq }=\frac{2 K _{1} K _{2}}{ K _{1}+ K _{2}}$