The circuit consists of two batteries with e. d.s. E1 = 4 V to E2 = 12 V, a rheostat with a sliding contact, the total resistance of which R is 1500 ohms, a conductor whose resistance is r = 200 ohms, and an ammeter, connected as shown in Fig. 128. To which pole of battery E2 should the sliding contact be connected and what position should it occupy on the rheostat so that the current through the ammeter is zero? What power will be dissipated in resistances R and r? Neglect the internal resistance of the batteries.

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