In a Van de Graaff type generator, a spherical metal shell is to be 15 × 106 V electrode. The dielectric strength of the gas surrounding the electrode is 5 × 107 Vm−1. The minimum radius of the spherical shell required is
a)
1 m
b)
2 m
c)
1.5 m
d)
3 m
Correct answer is option 'D'. Can you explain this answer?