Passage VI

A parallel-plale capacitor (PPC) stores electric charge on 2 separated plates when a voltage is applied across the plates. Figure 1 shows a PPC before (left) and after (right) it was filled with a dielectric (insulating mate­rial). The capacitance of an empty PPC, C0, is the amount of charge stored per unit of applied voltage. The capaci­tance of a filled PPC, Cκ, equals C0 multiplied by the dielectric constant, κ, of the filling material. Table 1 gives κ for 12 materials. Table 2 gives the dielectric strength, S (the maximum electric field strength at which a dielectric remains an insulator), for 7 of the materials.

34. Lightning strikes can occur when air between the ground and the base of a storm cloud is exposed to an electric field stronger than S for air. Suppose a certain storm cloud’s base is 300 m above the ground. Based on Table 2, approximately what minimum voltage would be present between the storm cloud’s base and the ground immediately before a bolt of lightning from this storm cloud strikes the ground？

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

It can be seen from the unit of S in table 2 that S=V/D (V stands for voltage voltage, D stands for distance), so V=SD;

From table 2, it can be known that air corresponds The S is 3.13. Then pay attention to convert 300 meters into millimeters, so S=300000 mm×3.13 kV/mm