A composite slab is prepared by pasting two plates of thickness L1 and L2 and thermal conductivites K1 and K2. The slabs have equal cross-sectional area. Find the equivalent conductivity of the composite slab.
It is equivalent to the series combination of 2 resistors.
∴ RS = R1 +R2
Resistance of a conducting slab, `R = l/(KA)`
`(L_1 + L_2)/(K_SA)=(L_1)/(K_1A)+ (L_2)/(K_2A)`
`(L_1 +L_2)/(K_s) = L_1/K_1 + L_2/K_2`
`(L_1 + L_2 )/K_s = (L_1K_2 + L_2K_1)/(K_1 xx K_2)`
`K_s = ((L_1 + L_2) (K_1 K_2))/(L_1k_2 + L_2K_1 `