The high school entrance examination physics experiment measures the rated power of small bulbs, and the expression of winning the middle school entrance examination is the key.

1. In the experiment of "measure the rated power of the small light bulb", the rated voltage of the small light bulb is U = 2.5 V.

(1) Figure A is the physical circuit diagram of Xiaoming's measurement of the rated power of the small light bulb. There is a wire connection error in the figure, please mark "×" on this wire, and correct __________ in the figure.

(2) Before closing the switch, the slider P should be at the _______ (optional "A" or "B") end.

(3) Close the switch, move the slider P until the voltmeter of shows 2.5 V, and the current expressed is as shown in Figure B of Question 23, which is _____ A, and the rated power of the small light bulb is __________W.

(4) Xiaohua designed the circuit shown in Figure C of Question 23 and completed the experiment. Please complete the following fill in the blanks (the power supply voltage remains unchanged, R1 and R2 are the sliding rheostat , and the maximum resistance of R2 is R0).

①Only close the switch ___________, adjust R2, so that the indication of the voltmeter is 2.5 V;

②Only close the switch ___________, make sure _____ does not move, adjust ______, so that the indication of the voltmeter is still 2.5 V;

③ Then adjust the slider P of R2 to the far left, and write down the indication of the voltmeter as U1; then adjust the slider P of R2 to the far right, and write down the indication of the voltmeter as U2. Then the expression P of the rated power of the small light bulb = ____________ (represented by U, R0, Ul, U2).

1. In the experiment of "measure the rated power of the small light bulb", the rated voltage of the small light bulb is U = 2.5 V.

(1) Figure A is the physical circuit diagram of Xiaoming's measurement of the rated power of the small light bulb. There is a wire connection error in the figure, please mark "×" on this wire, and correct __________ in the figure.

(2) Before closing the switch, the slider P should be at the _______ (optional "A" or "B") end.

(3) Close the switch, move the slider P until the voltmeter of shows 2.5 V, and the current expressed is as shown in Figure B of Question 23, which is _____ A, and the rated power of the small light bulb is __________W.

(4) Xiaohua designed the circuit shown in Figure C of Question 23 and completed the experiment. Please complete the following fill in the blanks (the power supply voltage remains unchanged, R1 and R2 are the sliding rheostat , and the maximum resistance of R2 is R0).

①Only close the switch ___________, adjust R2, so that the indication of the voltmeter is 2.5 V;

②Only close the switch ___________, make sure _____ does not move, adjust ______, so that the indication of the voltmeter is still 2.5 V;

③ Then adjust the slider P of R2 to the far left, and write down the indication of the voltmeter as U1; then adjust the slider P of R2 to the far right, and write down the indication of the voltmeter as U2. Then the expression P of the rated power of the small light bulb = ____________ (represented by U, R0, Ul, U2).

2. While reviewing the electrical knowledge, Xiao Ming did experiments on "measurement of electric power of small light bulbs" and "exploring the relationship between current, voltage and resistance" in laboratory . In the experiment, the power supply voltage used is 6V, the rated voltage of the small bulb is 3.8V, and the specification of the sliding rheostat is "30Ω 1A".

(1) In the experiment of "measuring the electric power of a small light bulb", Xiao Ming correctly connected the circuit according to the circuit diagram shown in Figure A. There are two wires missing from the real thing. Please use stroke lines instead of wires to make up, and connect the physical circuit in Figure B completely.

(2) The switch should be disconnected when connecting the circuit,The sliding piece P of the sliding rheostat should be placed at the extreme left (fill in "left" or "right").

(3) After closing the switch, move the slider of the varistor. When the indication of the voltmeter is 3.8V, the indication of the ammeter is as shown in Figure C, and the rated power of the small bulb is 1.52W.

(4) Move the slide P of the varistor, record the indications of several groups of corresponding voltmeters and ammeters, and draw the I-U image of the small light bulb as shown in Figure D. It can be seen from the image: when the voltage across the small bulb increases, the resistance of the small bulb increases (optionally fill in "increased", "unchanged" or "decreased"), if the voltage across the small bulb is 1.9V, Then the actual power of the small bulb is greater than 0.38W (optional "greater than", "less than" or "equal to").

(5) When doing the experiment of "exploring the relationship between current and resistance", the resistance values ​​of the four fixed-value resistors used by Xiaoming are 5Ω, 10Ω, 15Ω, and 20Ω respectively. He directly used the circuit connected to measure the electric power of the small light bulb to conduct experiments. He took off the small light bulb in the circuit, and the other components of the circuit were connected in the same way. If the safety of each element in the circuit is to be ensured, and the experiment can be successfully completed with four resistors, the voltage across the fixed-value resistor should be selected within the range of B.

A. U≤3V B. 2.4V≤U≤3V C. U≥3V D. 3V≤U≤6V.

2. (1) See above; (2) Disconnected; Left; (3) 1.52; (4) Larger; Greater than; (5) B.