Final answer:
The determination of the current IS1 requires using Kirchhoff's rules and the provided circuit values for E1 and E2. However, there is ambiguity due to the differing values given for E2. Once E2's value is clarified, the correct current can be calculated through simultaneous equations.
Step-by-step explanation:
To determine the current IS1 in the circuit, one would typically use Kirchhoff's rules—specifically the junction and loop rules—along with given values for electromotive forces (emfs) E1 and E2, and any provided resistances and internal resistances of the voltage sources. However, the correct value of E2 is essential for performing accurate calculations. The mixture of different values for E2 (15 V and 45 V given in the question and the additional information, respectively) creates an ambiguity that must be clarified before proceeding with the solution.
Assuming that the rest of the values and equations provided (such as Eq. (4) and (5)) match the ones in the student's problem and can be applied to the figure in question, these equations would be used to calculate the currents in the circuit, including IS1. The process would involve solving simultaneous equations derived from applying Kirchhoff's rules to the given circuit.