If two metallic plates of equal thicknesses and thermal conductivities \[{{K}_{1}}\]and \[{{K}_{2}}\] are put together face to face and a common plate is constructed, then the equivalent thermal conductivity of this plate will be [MP PMT 1991]

\[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{{{K}_{1}}{{K}_{2}}}\]

\[\frac{{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\]

\[\frac{2{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\]

\[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{2{{K}_{1}}{{K}_{2}}}\]

If two metallic plates of equal thicknesses and thermal conductivities

1.	If two metallic plates of equal thicknesses and thermal conductivities \[{{K}_{1}}\]and \[{{K}_{2}}\] are put together face to face and a common plate is constructed, then the equivalent thermal conductivity of this plate will be [MP PMT 1991]
A.	\[\frac{{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\]
B.	\[\frac{2{{K}_{1}}{{K}_{2}}}{{{K}_{1}}+{{K}_{2}}}\]
C.	\[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{{{K}_{1}}{{K}_{2}}}\]
D.	\[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{2{{K}_{1}}{{K}_{2}}}\]
Answer» C. \[\frac{{{(K_{1}^{2}+K_{2}^{2})}^{3/2}}}{{{K}_{1}}{{K}_{2}}}\]