(1) Turn off S and disconnect Sl. The resistor R 1 and the ammeter form a series circuit. According to ohm's law, the power supply u = IR1= 0.4a×15ω = 6V;

(2) When both switches S and Sl are closed, the resistor R 1 is connected in parallel with R2, and the ammeter measures the main current. It is known that the current representation number I: I' = 4: 7 and I=0.4A, so I' = 0.7a

According to ohm's law, if the current I2 flowing through resistor R2 is equal to I'-I = 0.7a-0.4a = 0.3a, then the electric power consumed by R2 when all switches are closed is P2 = UI2 = 6V× 0.3a =1.8w. 。

So the answer is: 6; 1.8.