An electron starts from rest 65.3cm from a fixed point chargewith Q = -0.132uC.

Question

An electron starts from rest 65.3cm from a fixed point chargewith Q = -0.132uC. How fast will the electron be moving when it isvery far away?

part 2 A cardiac defibrilator is used to shock a heart that isbeating erratically. A capacitor in this device is charged to 5970Vand stores 217J of energy. What is its capacitance? An electron starts from rest 65.3cm from a fixed point chargewith Q = -0.132uC. How fast will the electron be moving when it isvery far away?

part 2 A cardiac defibrilator is used to shock a heart that isbeating erratically. A capacitor in this device is charged to 5970Vand stores 217J of energy. What is its capacitance?

Explanation / Answer

PART 1:    distance, r = 65.3 cm = 0.653 m    q1 = - 1.6 X 10-19C    q2 = -0.132 X 10 -6 C    initial potential energy = (1/4o) ( q1 q2 / r ) =( 9 X 10 9 ) ( - 1.6 X 10-19 ) ( -0.132 X 10-6) / 0.653                                                                = 2.91 X 10 -25 J    But, kinetic energy at far off distance = initialpotential energy                (1/2) mv2 = 2.91 X 10 -25                    (1/2) ( 9.1 X 10 -31 )v2 = 2.91 X 10-25                                            v = 799.7 m/s PART 2:                      Energy stored in capacitor = (1/2) C V2                                    217 = (1/2) C ( 5970)2                                                C = 1.22 X 10 -5 F                                                    = 12.2 F                                                C = 1.22 X 10 -5 F                                                    = 12.2 F

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