Question

1) As a crude model for lightning, consider the ground to be one plate of a parallel-plate capacitor and a cloud at an altitude of 620 m to be the other plate. Assume the surface area of the cloud to be the same as the area of a square that is 0.55 km on a side. (a) What is the capacitance of this capacitor?

(b) How much charge can the cloud hold before the dielectric strength of the air is exceeded and a spark (lightning) results?

2) An electronic flash unit for a camera contains a capacitor with a capacitance of 760

Answer 1

Answer question

Answer 2

1)

C = ??*A/d, where ?? is the permittivity, d is the distance between the plates, and A is the area of the plates.

C = (??*(0.45km * 0.45km))/(470m)
= 3.815nF

q = CV
V = k*d = (3.0*10^6V/m)*(470m)
= 1.41TV (teravolts)

q = C*V = (3.815nF)*(1.41TV) = 5,379C

3)

current, I, is the amount of charge per unit time so I = Q/t --> tI = Q ---> (65)(.12) = 7.8 C

1 electron has a charge of 1.602*10^-19 so (1.602*10^-19)x = 7.8

x = 4.87*10^19 electrons