I was trying to find electrical potential of nodes (picture of circuit below), but I have problem. My referent node is "D". Therefore potential of node "B" is 12V. In this circuit there are 4 nodes, 2 of them are now known ("D" and "B") and two of them I have to find ("A" and "C"). My equation for node "A" is:-I1-I2-I3=0. Current I1 is current from branch with voltage source E2. Problem is,how to represent I1 using Ohm's law ((electrical potential difference)/Resistance) when there is no resistance? If there was resistor connected in series with E2 it wouldn't be problem to write equation, but there is no resistor so what should I do? I hope that someone will help me, it's very important

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