(1) After the key was turned off, it was observed that the readings of voltmeter and ammeter were 3 volts and 0.3 amps respectively. If the small light bulb marked "0.3A" is selected, it means that the small light bulb has been emitting normally and does not need to be adjusted; Then adjust the position of the sliding vane of the sliding rheostat to make the small light emit normally, indicating that the small light bulb marked "0.2A" is connected to the circuit;

(2) The voltmeter should be used in parallel with the small bulb to be measured, so it is connected to point ab in Figure A;

When the current in the circuit is 0.3A, the voltage across the small bulb is 3V. If the current in the small bulb is 0.2A by adjusting the sliding rheostat, then according to ohm's law I=UR, the voltage at both ends will be less than 3v, so the power supply voltage is 3V.

The selected range of voltmeter is 0 ~ 3v, and the minimum voltage division value is 0. 1V, so the indication of voltmeter is 2V.

The extra electric power of the small bulb p = UI = 2v×0.2a = 0.4w；;

So the answer is: when the current is 0.3 A, the small lamp is not in a normal luminous state; 0.2Aab； 3; 0.4.