Question

Figure shows a copper rod joined to a steel rod. The rods have equal length and and the equal cross sectional area. The free end of the copper rod is kept at `0^(@)C` and that of the steel rod is kept at `100^(@)C` . Find the temperature at the junction of the rods. conductivity of copper `=390WM^(-1).^(@)C^(-1)` and that of steel `=46Wm^(-1).^(@)C^(-1)` .

A. will be nore than `50^(@)`C
B. will be less than `50^(@)`C
C. will b `50^(@)`C
D. may be nore or less than 50 c depending upon the size of rods

Answer 1

Correct Answer - A
`K_(C) gt K_(B)`
`therefore R_(C) lt R_(B)`
Temperature difference across copper `= HR_(C) = (TD)_(C)`
And temperature difference across brass `= HR_(B) = (TD)_(B)`
Heat current H will be same in both , as they are in series.
Since R_(C) lt R_(B)
`therefore (TD)_(c) lt (TD)_(B)`
Or temperature of junction is more than `50^(@)C`.