In a circuit shown in Fig. 3.54 resistances \(R_{1}\) and \(R_{2}\) are known, as well as emf's \(\mathscr{E}_ {1}\) and \(\mathscr{E}_{2} .\) The internal resistances of the sources are negligible. At what value of the resistance \(R\) will the thermal power generated in it be the highest? What is it equal to?