In circuit of this exercise the negative terminals of the sources are connected to ground. Is this a requirement for mesh analysis? What would happen to the mesh currents if the positions of E1 and R1...

In circuit of this exercise the negative terminals of the sources are connected to ground. Is this a requirement for mesh analysis? What would happen to the mesh currents if the positions of E1 and R1 in Figure 7.1 were swapped?

Extracted text: A R4 PR1 R2 R3 R5 LE1 E2 Figure 7.1 B