The coefficient of the thermal conductivity of copper is 9 times that of steel . In the composite sylindrical bar shown in the figure , what will be the temperature at the junction of copper and steel ?

Options

A. `25^(@)C`
B. `33^(@)C`
C. `75^(@)C`
D. `67^(@)C`

Answer

C

Explanation

The heat current `=("Thermal P.D"("temp. difference"))/("Thermal resistance")`
`I_("thermal")` Thermal `P.D.xx(sigmaA)/(l)` where `rho=1//sigma`.
`I=((100^(@)C-T)9sigma*A)/(18cm)=((T-0^(@)C)sigmaA)/(6cm)`
`rArr4T=300^(@)CrArrT=75^(@)C`.