B) Once the capacitor is charged, how much energy is stored in the capacitor? C)

Question

B) Once the capacitor is charged, how much energy is stored in the capacitor?

C) Assume the capacitor is a parallel-plate capacitor with vacuum between its two plates. An electron is released from the negatively charged plate and flies toward the positive plate. How fast would the electron be traveling when it reaches the positive plate?

D) Once the capacitor is charged, the voltage source is first disconnected, and then the two terminals of the capacitor are connected by a copper wire so that the capacitor is rapidly discharged, releasing all its stored energy. If it took 10 micro-seconds for the capacitor to discharge completely, what was the average power dissipation during these 10 micro-seconds?

Explanation / Answer

Here ,

C = 20 uF

V = 5000 V

A) charge on teh capacitor = C * V

charge on teh capacitor = 20 *10^-6 * 5000 C

charge on teh capacitor = 0.1 C

B)

energy stored in capacitor = 0.5 * C * V^2

energy stored in capacitor = 0.5 * 20 *10^-6 * 5000^2

energy stored in capacitor = 250 J

C)
let the speed of electron is u

Using work energy theorum

0.5 * m * u^2 = V * e

0.5 * 9.11 *10^-31 * u^2 = 5000 * 1.602 *10^-19

solving for u

u = 4.193 *10^7 m/s

the speed of electron is 4.193 *10^7 m/s

D)

average power dissipation = energy stored/time

average power dissipation = 250/(10 *10^-6)

average power dissipation = 2.5 *10^7 W

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