[填空题]
Dry air will break down and generate a 6ckkdo8p k7l7y v i2au4;nu/tspark if the 8;naz f2isv gecu8pc*n) 5 s7eelectric field exceeds aboutueg58*nzspaf8)vi n 7;2ec sc $ 3\times10^{6 }\,N/C$. How much charge could be packed onto a green pea (diameter 0.75 cm) before the pea spontaneously discharges? [Hint: Eqs. 16–4 work outside a sphere if r is measured from its center.] $ \times10^{-9 }\,C$
