A student performing the experiment concerning capacitors and RC circuits was gi
ID: 1551564 • Letter: A
Question
A student performing the experiment concerning capacitors and RC circuits was given the graph shown below to analyze. For purposes of significant figures, please consider the time readings as exact numbers. The capacitor in the circuit had a capacitance of 0.200 F. (a) What is the setting of the power supply? (b) Determine the time constant of the RC combination. (c) Determine the resistance of the resistor in the circuit. (d) Determine the charge on the capacitor at t = 40.0 s. (e) After the capacitor is fully discharged, it is charged through the same resistor. During charging determine the current through the resistor at t = 85 seconds.Explanation / Answer
a) Power supply is 8 volts, the maximum potential possible
b) time constant is 63% of the maximum voltage (8) which is 5.04volts , the time is 20s
c) resistance is t = RC
R = t /C = 20 / 0.2 = 100 ohms
d) At 40s time, the voltage across the capacitor is 3.25 volts
Charge Q = CV = (0.2)(3.25) = 0.65 coulombs
e) Taking the voltage as 1.25 volts across the resistor at t = 85s then current is
I = V/ R = 1.25 / 100 = 1.25 E -3 A or 0.0125 A
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