Consider a compound slab consisting of two different materials having equal thicknesses and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is . . . . . .. .

Options

A. `4/3K`
B. `2/3K`
C. `sqrt(3)K`
D. 3 K

Answer

A

Explanation

For series connection,
`(L_(1)+L_(2))/(K_(s))=(L_(1))/(K_(1))+(L_(2))/(K_(2))`
`:.(2L)/(K_(s))=(L)/(K)+(L)/(2K)" "[becauseL_(1)=L_(2)=L]`
`:.(2)/(K_(s))=1/K+1/(2K)`
`:.(2)/(K_(s))=(2+1)/(2K)+(3)/(2K)`
`:.K_(s)=(4K)/(3)`