Question

A compound rod is formed of a steel core of diameter `1cm` and outer casing is of copper, whose outer diameter is `2cm`. The length of this compound rod is `2m` and one end is maintained as `100^(@)C` and the end is at `0^(@)C`. If the outer surface of the rod is thermally insulated, then heat current in the rod will be (Given thermal conductivity of steel `j=12cal//m//k//s`, thermal conductivity of copper `=92cal//m//k//s`
A. `2cal//s`
B. `1.13cal//s`
C. `1.42cal//s`
D. `2.68cal//s`

Answer 1

(b) `Q=Q_("steel")+Q_("copper")`
`(=12 pi (0.5)^(2)xx10^(-4)xx100)/2+(92pi(1^(2)-0.5^(2))xx10^(-4)xx100)/2`
`=1500pixx10^(-4)+3450pixx10^(-4)=1.13cal//s`