Two identical metal wires of thermal conductivities K1 and K2 respectively are connected in series. The effective thermal conductivity of the combination is:
1
\(\frac{K_1 K_2}{K_1 + K_2}\)
2
\(\frac{2K_1 K_2}{K_1 + K_2}\)
3
\(\frac{K_1+ K_2}{2K_1 K_2}\)
4
\(\frac{K_1+ K_2}{K_1 K_2}\)