A heat flux of \(4000\) J/s is to be passed through a copper rod of length \(10 \, \text{cm}\) and area of cross-section \(100 \, \text{sq.cm}\). The thermal conductivity of copper is \(400 \, \text{W/m}^\circ\text{C}\). The two ends of this rod must be kept at a temperature difference of
1
\(1^\circ \text{C}\)
2
\(10^\circ \text{C}\)
3
\(100^\circ \text{C}\)
4
\(1000^\circ \text{C}\)