Discussion Forum
Que.  A cylinder of radius r and made of material of thermal conductivity k 1 is surrounded by a cylindrical shell of inner radius r and outer radius 2r. This outer shell is made of a material of thermal conductivity k 2. Net conductivity would be 
a.  k 1 + 3 k 2/4 
b.  k 1 + k 2/4 
c.  k 1 + 3k 2 
d.  k 1 + k 2 
Correct Answer:k 1 + 3 k 2/4
