A cylinder of radius `R` made of a material of thermal conductivity `K_(1)` is surrounded by cylindrical shell of inner radius `R` and outer radius `2R` made of a material of thermal con-ductivity `K_(2)` The two ends of the combined system are maintained at two differnet tem-peratures There is no loss of heat across the cylindrical surface and system is in steady state What is the effective thermal conductivity of the system
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Explanation

`A_(1) = pi R^(2) ,A_(2) = pi (4R^(2) -R^(2))`
Two cylinders are in parallel
`:. K_(eff) (A_(1)+A_(2)) =K_(1) A_(1) +K_(2) A_(2)`
`K_(eff) =(K_(1)piR^(2)+K_(2)3piR^(2))/(piR^(2)+3piR^(2)),i.eK_(eff) = ((K_(1)+3K_(2)))/(4)` .