Physics
Kirchhoff's Law
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Experiment 12 - Circuit with Capacitor

Consider the circuit shown...

 Circuit with a capacitor. (Enlarge) Circuit diagram circuit with capacitor.

If you press the pushbutton switch S1, the capacitor is charged via R1. Only after a few seconds is it fully charged. The circuit becomes a function of time!

When you open S1, the capacitor discharges via the resistor R2. The respective voltages over time are shown in the illustrations....

 Voltage charging capacitor at R2. Voltage discharging capacitor at R2.

The resistor R2 forms a loop with the capacitor. If you measure the voltage across R2, you realize quickly that it behaves in the same way as the voltage across the capacitor.

You would obtain a comparable result when you measure the current. Therefore, you can state for the Kirchhoff's laws...

 Kirchhoff's laws apply to any snapshot of current and voltage!

In the next experiment, you examine a transistor in a circuit...