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1) What is the approximate magnitude of the electric field between the charge ce

ID: 2006269 • Letter: 1

Question

1) What is the approximate magnitude of the electric field between the charge center and the ground?

A) 4 x 10^4 V/m                B) 4 x 10^5 V/m

C) 4 x 10^6 V/m                D) 4 x 10^7 V/m

A) B) C) D) Storm clouds build up large negative charges, as described in the chapter. The charges dwell in charge centers, regions of concentrated charge. Suppose a cloud has -25 C in a 1.0-km-diameter spherical charge center located 10 km above the ground, as sketched in the figure. The negative charge center attracts a similar amount of positive charge that is spread out on the ground below the cloud. The charge center and the ground function as a charged capacitor, with a potential difference of approximately 4 x 10^8 m The large electric field between these two ^'electrodes^' may ionize the air, leading to a conducting path between the cloud and the ground. Charges will flow along this conducting path, causing a discharge of the capacitor - a lightning strike. 1) What is the approximate magnitude of the electric field between the charge center and the ground? A) 4 x 10^4 V/m B) 4 x 10^5 V/m C) 4 x 10^6 V/m D) 4 x 10^7 V/m 2) What is the approximate capacitance of the charge center-ground system? 3) If the cloud transfers all of its charge to the ground via several rapid lightning flashes lasting a total of 1.90 s, what is the average power?

Explanation / Answer

1 ) Electric field between the charge and the center is                  E = V / d potential difference of a charged capacitor is V = 4*10^8 V distance d = 10 km                  E = 4*10^8 V / 10 *10^3 m                        = 4*10^4 V /m 2 ) Capacitance of the charge center ground system is                charge is q = -25 C          Capacitor is C = Q / V                                     = 25 C / 4*10^8 V                                      = 6.25*10^-8 F 3 ) Energy stored in a capcitor is E = 1/2 CV^2                         = 1/2 * 6*10^-8 F * ( 4*10^8)^2                        = 50*10^8 J           Average Power is P = E / t                                           = 50*10^8 J / 1.9 s                                            = 2.7*10^9 W                                             = 2.7 GW