Menu Course Contents . HW 11 - ch.21 Part 1 - Switching on a Circuit ?Notes | Bo

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Menu Course Contents . HW 11 - ch.21 Part 1 - Switching on a Circuit ?Notes | Bookmark à Evaluate ecommunicateghint einfo Consider the RC circuit in the figure below. The switch was at position a for a long period of time and it is suddenly switched to position b at timet 0 For each statement select True or False. The current through the resistor equals the current across the capacitor at all times In the instant after the switch is thrown the voltage across the resistor is zero v In the instant after the switch is thrown, the voltage across the capacitor is zero. In the instant after the switch is thrown the current across the capacitor is zero. Submit Answer Incorrect. Tries 1/10 Previous Tries What is Ve at time t 2.00 ms? use the following data : R-466.5 , ? 4,00 pF, Vb-2.75 Submit Answer Tries 0/10 What is the total energy dissipated by the resistor R after the switch is thrown? Submia Anawer Tries 0/10 Using the same data as before, consider the case when the switch is in position b for a long time, and then it is switched to position a at time t 0. What is Vc at time t 2.00 ms? Submit Ansswer Tries 0/10 This discussion is closed. Send Feedback 4/12/2015 O Ask me anything

Explanation / Answer

1. "The current through the resistor equals the current across the capacitor at all times."
Currents are not "across", they are through or from.
True, the current from the capacitor equals the current through the resistor, they are in series.

2. "In the instant after the switch is thrown the voltage across the resistor is zero."
False, it is equal to Vb

3. "In the instant after the switch is thrown the current across the capacitor is zero."
"current across" is a meaningless term.

False , Current from the capacitor is NOT zero.

4. "In the instant after the switch is thrown, the voltage across the capacitor is zero."
FALSE, it is equal to Vb

problem1 )

Assuming switch moves from a to b (discharging) at t=0, Vc(t) = Vb*e^(-t/RC)).

at t = 2

Vc = 2.75*e^(-2*10-3s / [466.5*4*10-6F])

Vc = 2.75*e^(-1.07) = 0.943 V

problem2)

E = 1/2 CV2

E = 0.5*4*10-6*2.752 = 1.5125*10-5 J

problem 3)

Vb - Vc = 2.75 - 0.943 = 1.807 V

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