When the closed s 1 s2 is connected to the 1 ammeter, the internal resistance R of the electromotive force E of the power supply is too small, which is the line A..

When the closed s 1 s2 is connected to a 2-amp meter, the electromotive force E of the power supply is measured externally, and the accurate internal resistance r=R+r is the B line.

The electromotive force of power supply e =1.5vr = (1.5-0/(1-0) =1.5Ω.