A cubical box of volume `216cm^(3)` is made up of `0.1cm thick wood, The inside is heated electrically by 100W heater. It is found that the temperature difference between the inside and the outside surface `5^(@)C` . In steady state . Assuming that the entire electrically energy spent appears as heat, find the thermal conductivity of the material of the box.

Answer

A, B, C

Explanation

`V=216 cm^(3), a=6 cm,
Surface area `=6 a^(2)=6xx36xx10^(-4) m^(2)`
`l=0.1cm`
`(Q)/(T)=(kA(T_1-T_2))/(l)`
implies 100=(kxx6xx36xx10^(-4)xx5)/(0.1xx10^(-2))`
`implies 100=kxx6xx36xx10^(-1)xx5`
`implies k=(100)/(6xx36xx5xx10^(-1))`
`=(100xx10)/(6xx36xx5)`
`=0.9259 w//m^(@)C`.