According to the table, there are voltage, conductor length, cross-sectional area and material, so they think that the factors affecting the current may be: voltage, conductor length, conductor material and conductor cross-sectional area;

② By analyzing and comparing the data in Table 1, Table 2 or Table 3, it can be concluded that the material, length and cross-sectional area of the conductor are the same, but the voltage at both ends of the conductor is different, which makes the voltage several times the original, and the current passing through the conductor becomes the original basic, so it can be concluded that the current passing through the conductor is directly proportional to the voltage at both ends of the conductor for the same conductor.

(3) By analyzing and comparing the data in Table 1, Table 2 and Table 3, it can be known that the material and cross-sectional area of the conductor are the same, but the length is different, and the ratio of voltage to current is different, and the longer the length, the greater the ratio; Therefore, it can be concluded that different conductors (the same material and cross-sectional area, but different lengths) have different ratios of voltage at both ends of the conductor to current passing through the conductor, and the longer the length, the greater the ratio.

④ To study the relationship between the current passing through the conductor and the cross-sectional area of the conductor, it is necessary to ensure that the length of the conductor is constant and the cross-sectional area is different, so the length is the same as that in Table 2, that is, 1.2m, and the cross-sectional area can be selected as 0.2mm2 and 0.4mm2, as shown in the following table:

Conductor length (m) cross-sectional area (mm 2) d1.20.2e1.20.4 So the answer is:

① Voltage, conductor length, conductor material and conductor section;

② For the same conductor (the same material, length and cross-sectional area), the current passing through the conductor is directly proportional to the voltage at both ends of the conductor.

③ Different conductors (the same material and cross-sectional area, but different lengths) have different ratios between the voltage at both ends of the conductor and the current passing through the conductor, and the longer the length, the greater the ratio.

④ See the table above.