(1) The voltmeter should be connected in parallel with the bulb, and the sliding rheostat has been connected to the upper terminal and connected to the lower terminal, as shown in the figure:

(2) When connecting the circuit, the switch should be turned off;

Because B is terminated below the sliding rheostat, before the switch is closed, the sliding vane of the sliding rheostat should be adjusted to the left end, that is, the A end;

(3) As shown in Figure 2, the measuring range of ammeter is 0 ~ 0.6A, the dividing value is 0.02A, and the indicator is 0.3A, so r = UI = 3.8V0.3A =12.7ω;

(4) In the experimental platform, the voltage U, current I, resistance and other items when the light bulb normally emits light are shown in the following table:

The voltage across the bulb U/V passes through the current of the bulb I/A The resistance of the bulb R/ω 3.8? ? ⑤ Because the filament resistance increases with the increase of temperature, in order to explore the relationship between the current in the conductor and the voltage at both ends of the conductor, it is necessary to use a fixed value resistor instead of a small bulb to complete the experiment;

There is no voltmeter in the experiment, so an ammeter and a fixed-value resistor can be used instead of the voltmeter and connected in parallel with the fixed-value resistor, as shown in the figure:

.

Therefore, the answers are: ① See the above picture; 2 disconnect; a； ③ 12.7; ④ See the above table; ⑤ Fixed value resistance; See the picture above.