So the answer is: disconnect.
(2) As can be seen from the physical drawing, the sliding rheostat is connected to the terminal below the right end, and the slider of the sliding resistor should be moved to the other side of the lower terminal, where the resistance is the largest, that is, the left end.
As can be seen from the figure, the voltmeter deflects to the left, so the positive and negative poles of the voltmeter are reversed; The deflection angle of ammeter pointer is too large, indicating that the selected range of ammeter is too small.
So the answer is: left; The positive and negative poles are reversed; The range selection is too small (or the measuring voltage is too large);
(3) In order to make the bulb glow normally, the sliding blade of the sliding rheostat should be moved to make the voltmeter indicate the rated voltage of the bulb to be 3.8V. As can be seen from the figure, the selection range of the ammeter is 0 ~ 0.6A, and its partial pressure value is 0.02A As can be seen from the pointer position, the current indication at this time is 0.28A, so p = UI = 3.8V× 0.28a =1.
So the answer is: 3.8; 0.28; 1.064.
(4) As shown in the figure, the sliding resistor and the measured resistor are connected in series, and the voltmeter and the measured resistor are connected in parallel.
(5) The specific experimental steps are as follows:
(1) close the circuit, first adjust the sliding rheostat to make the resistance of the access circuit 0, and write down the indicator U 1 of the voltmeter, which is the power supply voltage;
(2) adjust the sliding rheostat, so that the resistance connected to the circuit is the maximum value R0, and write down the instruction U2 of the voltmeter, and the circuit current is U 1? U2？ r0；
(3) resistance to be measured RX=U2U 1? U2R0=U2R0U 1？ U2。
Note: If the sliding rheostat is adjusted to maximize the resistance of the access circuit, write down the indicator U 1 of the voltmeter, then adjust the sliding rheostat to make the resistance of the access circuit zero, and write down the indicator U2 of the voltmeter. The result expression is U 1R0U2? U 1。