Q.

Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K1 and K2. The thermal conductivity of the composite rod will be        [2017]

1 3(K1+K2)2  
2 K1+K2  
3 2(K1+K2)  
4 K1+K22  

Ans.

(4)

Equivalent thermal conductivity of the composite rod in parallel combination will be,

K=K1A1+K2A2A1+A2=K1+K22