Exercises - Capacitor

Part 1: Checkbox tasks - Capacitors

- only one is right at a time!

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What is the time constant Ƭ in this series connection shown?

RC in series

 Ƭ = 0,2 s

 Ƭ = 96 ms

 Ƭ = 2 s

 Ƭ = 0,96 s

 Ƭ = 20 ms

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A 50 µF and an 80 µF capacitor are connected in series. What is the resulting capacity?

 C_Res = 120 µF

 C_Res = 130 µF

 C_Res =30 mF

 C_Res = 30,77 µF

 C_Res = 30 µF

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A 50 µF and an 80 µF capacitor are connected in parallel. What is the resulting capacity?

 C_Res = 130 µF

 C_Res = 30,77 µF

 C_Res = 30 mF

 C_Res = 30 µF

 C_Res = 120 µF

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Part 2: Capacitor connected to DC voltage

A capacitor with a capacitance of C = 4.7 µF is charged via a resistor of 1 kΩ. The following diagram shows the capacitor voltage as a function of time t.

Capacitor in DC Circuit - exercise

Determine the time constant of this resistor-capacitor series
Determine the instantaneous current at time t = 0 s
Determine the instantaneous current at time t = 5 ms

You can determine the time constant τ:
Either via τ = R · C = 1 kΩ · 4.7 µF = 4,7 ms
or graphically:

Capacitor in DC Circuit - solution

At time t = 0 s, the charging current is only limited by the ohmic resistance R of 1 kΩ:
I ( t = 0 ms) = U / R = 100 V / 1 kΩ  =  0,1 A

At time t = 5 ms you get for V_C ≈ 73 V, therefore V_R ≈ 27 V

=> I (5 ms) = 27 V / 1 kΩ  =  0,27 A